%0 journal article %@ 2075-4442 %A Kandemir, S., Yöyler, S., Kumar, R., Antonov, M., Dieringa, H. %D 2024 %J Lubricants %N 2 %P 52 %R doi:10.3390/lubricants12020052 %T Effect of Graphene Nanoplatelet Content on Mechanical and Elevated-Temperature Tribological Performance of Self-Lubricating ZE10 Magnesium Alloy Nanocomposites %U https://doi.org/10.3390/lubricants12020052 2 %X Magnesium (Mg) and graphene in alloy formulations are of paramount importance for lightweight engineering applications. In the present study, ZE10 Mg-alloy-based nanocomposites reinforced with graphene nanoplatelets (GNPs) having a thickness of 10–20 nm were fabricated via ultrasound-assisted stir casting. The effect of GNP contents (0.25, 0.5, and 1.0 wt.%) on the microstructure, Vickers hardness, and tensile properties of nanocomposites was investigated. Further, tribological studies were performed under a ball-on-disc sliding wear configuration against a bearing ball counterbody, at room and elevated temperatures of 100 °C and 200 °C, to comprehend temperature-induced wear mechanisms and friction evolution. It was revealed that the GNP addition resulted in grain coarsening and increased porosity rate of the Mg alloy. While the composites exhibited improved hardness by 20–35% at room temperature and 100 °C, a minor change was observed in their hardness and tensile yield strength values at 200 °C with respect to the GNP-free alloy. A notable improvement in lowering and stabilizing friction (coefficient of friction at 200 °C~0.25) and wear values was seen for the self-lubricating GNP-added composites at all sliding temperatures. The worn surface morphology indicated a simultaneous occurrence of abrasive and adhesive wear mode in all samples at room temperature and 100 °C, while delamination and smearing along with debris compaction (tribolayer protection) were the dominant mechanisms of wear at 200 °C. Inclusively, the results advocate steady frictional conditions, improved wear resistance, and favorable wear-protective mechanisms for the Mg alloy–GNP nanocomposites at room and elevated temperatures. %0 journal article %@ 1751-6161 %A Kujur, M.S., Krishnan, A.V., Manakari, V., Parande, G., Dieringa, H., Mallick, A., Gupta, M. %D 2024 %J Journal of the Mechanical Behavior of Biomedical Materials %P 106424 %R doi:10.1016/j.jmbbm.2024.106424 %T Scope of magnesium ceria nanocomposites for mandibular reconstruction: Degradation and biomechanical evaluation using a 3-dimensional finite element analysis approach %U https://doi.org/10.1016/j.jmbbm.2024.106424 %X Magnesium/Ceria nanocomposites (Mg/xCeO2 NCs (x = 0.5 %, 1 % and 1.5 %)) prepared by using powder metallurgy and microwave sintering method are assessed for their corrosion rate for a period of 28 days. As per the immersion tests results, the addition of ceria nanoparticles to pure Mg, brought about a noteworthy improvement to corrosion resistance. A corrosion rate of approximately 0.84 mm/year for Mg/0.5CeO2 and 0.99 mm/year for Mg/1.0CeO2 nanocomposites were observed. Another aspect of the study involves employing the simulation method i.e. finite element analysis (FEA) to compare the stress distribution in magnesium-ceria nanocomposite based screws and circular bars especially for Mg/0.5CeO2 and Mg/1.0CeO2. Further, the simulation also gives a perception of the impact of masticatory forces, the biting force and shear stress exerted on the Mg/0.5CeO2 and Mg/1.0CeO2 based screws. The simulations results show that the screws showed an acceptable level of stresses for a biting force up to 300 N. The circular bar as well kept its stresses at acceptable levels for the same load of 300N. The shear stress results indicated that a biting force up to 602 N can be safely absorbed by Mg/0.5CeO2 screw. The comprehensive approach allows for a better understanding of the corrosion behavior, stress distribution, and mechanical properties of the Mg/CeO2 nanocomposites, enabling the development of effective temporary implants for craniofacial trauma fixation that can withstand normal physiological forces during mastication. The study reported in this paper aims to target Mg/xCeO2 NCs for temporary implants for craniofacial trauma fixation. %0 journal article %@ 0921-5093 %A Shi, H., Yang, L., Huang, Y., Zhou, S., Wang, K., Liu, C., Gavras, S., Xiao, L., Willumeit-Römer, R., Dieringa, H., Hort, N. %D 2024 %J Materials Science and Engineering: A %P 146065 %R doi:10.1016/j.msea.2023.146065 %T Insights into creep behavior of Mg–14Gd–1Zn–0.4Zr (wt.%) alloy containing β- and γ-type precipitates %U https://doi.org/10.1016/j.msea.2023.146065 %X Compressive creep tests were performed on sand-cast and peak-aged Mg–14Gd–1Zn–0.4Zr (wt.%) alloys at 250 °C in this study. The microstructures before creep and at the secondary creep stage were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that plenty of fine precipitates, especially β′-series precipitates or a combination of β-type and γ′ precipitates, could effectively enhance the creep resistance of Mg alloys. Large amounts of β'+β′F precipitate chains in the regions near grain boundaries of the sand-cast alloy blocked the motion of -type dislocations, while the interaction of basal and prismatic dislocations could be inhibited by synergy of γ′ and β-type precipitates. In contrast, transformation of β′-series precipitates to β1 or β precipitates in the peak-aged alloy reduced their capacity to impede the dislocation movement, seemingly presenting worse microstructures for creep resistance. However, the peak-aged alloy exhibited a uniform distribution of numerous semi-coherent β1 precipitates and dense rectangular networks composed of γ′ and β-type precipitates within the whole grain, which was superior to the uneven distribution of β-type and γ′ precipitates as well as a lack of ample precipitates at the center of grain in the sand-cast alloy. Thus, the peak-aged Mg–14Gd–1Zn–0.4Zr alloy obtained better creep resistance than the sand-cast alloy to some extent. %0 journal article %@ 1996-1944 %A Dieringa, H., Nienaber, M., Giannopoulou, D., Isakovic, J., Bohlen, J., Kujur, M.S., Ben Khalifa, N., Klein, T., Gneiger, S. %D 2024 %J Materials %N 2 %P 500 %R doi:10.3390/ma17020500 %T Novel Magnesium Nanocomposite for Wire-Arc Directed Energy Deposition %U https://doi.org/10.3390/ma17020500 2 %X Magnesium alloys play an essential role in metallic lightweight construction for modern mobility applications due to their low density, excellent specific strength, and very good castability. For some years now, degradable implants have also been made from magnesium alloys, which, thanks to this special functionality, save patients a second surgery for explantation. New additive manufacturing processes, which are divided into powder-based and wire-based processes depending on the feedstock used, can be utilized for these applications. Therefore, magnesium alloys should also be used here, but this is hardly ever implemented, and few literature reports exist on this subject. This is attributable to the high affinity of magnesium to oxygen, which makes the use of powders difficult. Therefore, magnesium wires are likely to be used. In this paper, a magnesium-based nanocomposite wire is made from an AM60 (Mg-6Al-0.4Mn) (reinforced with 1 wt% AlN nanoparticles and containing calcium to reduce flammability), using a high-shear process and then extruded into wires. These wires are then used as feedstock to build up samples by wire-arc directed energy deposition, and their mechanical properties and microstructure are examined. Our results show that although the ductility is reduced by adding calcium and nanoparticles, the yield strength in the welding direction and perpendicular to it is increased to 131 MPa. %0 journal article %@ 2213-9567 %A Shi, H., Huang, Y., Yang, L., Liu, C., Dieringa, H., Lu, C., Xiao, L., Willumeit-Römer, R., Hort, N. %D 2023 %J Journal of Magnesium and Alloys %P 3161-3173 %R doi:10.1016/j.jma.2023.09.005 %T Microstructural evolution of Mg–14Gd–0.4Zr alloy during compressive creep %U https://doi.org/10.1016/j.jma.2023.09.005 %X The present work reports the creep behavior and microstructural evolution of the sand-cast Mg–14Gd–0.4Zr alloy (wt.%) prepared by the differential pressure casting machine. Their compressive creep tests at 250 °C were performed under various applied stresses (i.e., 60, 80 and 100 MPa). Among them, the sand-cast Mg–14Gd–0.4Zr samples examined under 250 °C/80 MPa for 39 and 95 h, respectively, were chosen to systemically analyze their creep mechanisms using high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The obtained results showed that the enhancement of creep resistance can be mainly attributed to the coherent β' and β'F phases with an alternate distribution, effectively impeding the basal dislocations movement. However, with the creep time increasing, the fine β'+β'F precipitate chains coarsened and transformed to semi-coherent β1 phase and even to large incoherent β phase (surrounded by precipitate-free areas) in grain interiors. The precipitate-free zones (PFZs) at grain boundaries (GBs) were formed, and they could expand during creep deformation. Apart from the main cross-slip of basal and prismatic dislocations, type dislocations were activated and tended to distribute near the GBs. The aforementioned phenomena induced the stress concentrations, consequently leading to the increment of the creep strain. %0 journal article %@ 2213-9567 %A Kandemir, S., Bohlen, J., Dieringa, H. %D 2023 %J Journal of Magnesium and Alloys %N 7 %P 2518-2529 %R doi:https://doi.org/10.1016/j.jma.2023.06.004 %T Influence of recycled carbon fiber addition on the microstructure and creep response of extruded AZ91 magnesium alloy %U https://doi.org/https://doi.org/10.1016/j.jma.2023.06.004 7 %X In this study, the recycled short carbon fiber (CF)-reinforced magnesium matrix composites were fabricated using a combination of stir casting and hot extrusion. The objective was to investigate the impact of CF content (2.5 and 5.0 wt.%) and fiber length (100 and 500 µm) on the microstructure, mechanical properties, and creep behavior of AZ91 alloy matrix. The microstructural analysis revealed that the CFs aligned in the extrusion direction resulted in grain and intermetallic refinement within the alloy. In comparison to the unreinforced AZ91 alloy, the composites with 2.5 wt.% CF exhibited an increase in hardness by 16–20% and yield strength by 5–15%, depending on the fiber length, while experiencing a reduction in ductility. When the reinforcement content was increased from 2.5 to 5.0 wt.%, strength values exhibited fluctuations and decline, accompanied by decreased ductility. These divergent outcomes were discussed in relation to fiber length, clustering tendency due to higher reinforcement content, and the presence of interfacial products with micro-cracks at the CF-matrix interface. Tensile creep tests indicated that CFs did not enhance the creep resistance of extruded AZ91 alloy, suggesting that grain boundary sliding is likely the dominant deformation mechanism during creep. %0 journal article %@ 0921-5093 %A Shi, H., Huang, Y., Yang, L., Liu, C., Dieringa, H., Lu, C., Xiao, L., Willumeit-Römer, R., Hort, N. %D 2023 %J Materials Science and Engineering: A %P 145422 %R doi:10.1016/j.msea.2023.145422 %T Compressive creep behavior and microstructural evolution of sand-cast and peak-aged Mg–12Gd–0.4Zr alloy at 250 °C %U https://doi.org/10.1016/j.msea.2023.145422 %X Magnesium (Mg) alloys with high concentrations of Gd additions are known to exhibit high strength and good creep resistance at elevated temperatures. However, the main mechanisms including microstructural evolution and dislocation configurations for clarifying the low creep rates of Mg–Gd–Zr alloys are still controversial. The present work investigates the compressive creep behavior of both the sand-cast and peak-aged Mg–12Gd–0.4Zr (wt.%) alloys at a fixed temperature of 250 °C under the applied stress range of 60–100 and 80–120 MPa, respectively. It is revealed that β' and β'F precipitates distribute alternately forming precipitate chains in Mg–Gd–Zr alloys. Furthermore, β'+β'F precipitate chains led to the honeycomb-like structure in the sand-cast alloy during the creep process, improving its creep resistance to some extent. Nevertheless, weakly strengthening β1 precipitates occurred and detrimental β phases coarsened, which weakened the creep performance of the sand-cast alloy. However, the slight improvement of creep resistance in the peak-aged Mg–12Gd–0.4Zr alloy can be mainly attributed to the formation of precipitate-free zones (PFZs) and also the premature coarsening of β'+β'F precipitate chains. During creep, the cross slip of basal and prismatic dislocations become the dominant creep mechanism for the sand-cast alloys. By contrast, the cross-slip of basal dislocations and pyramidal dislocations is the dominant creep mechanism for the peak-aged alloys, which was arrested by precipitates then strengthening the creep resistance of peak-aged alloys. %0 journal article %@ 2213-9567 %A Fan, L., Zhou, M., Lao, W., Zhang, Y., Dieringa, H., Zeng, Y., Huang, Y., Quan, G. %D 2023 %J Journal of Magnesium and Alloys %R doi:10.1016/j.jma.2023.02.011 %T Improving the ductility and toughness of nano-TiC/AZ61 composite by optimizing bimodal grain microstructure via extrusion speed %U https://doi.org/10.1016/j.jma.2023.02.011 %X In this study, the nano-TiC/AZ61 composites with different heterogeneous bimodal grain (HBG) structures and uniform structure are obtained by regulating the extrusion speed. The effect of HBG structure on the mechanical properties of the composites is investigated. The increasing ductility and toughening mechanism of HBG magnesium matrix composites are carefully discussed. When the extrusion speed increases from 0.75 mm/s to 2.5 mm/s or 3.5 mm/s, the microstructure transforms from uniform to HBG structure. Compared with Uniform-0.75 mm/s composite, Heterogeneous-3.5 mm/s composite achieves a 116.7% increase in ductility in the plastic deformation stage and almost no reduction in ultimate tensile strength. This is mainly because the lower plastic deformation inhomogeneity and higher strain hardening due to hetero-deformation induced (HDI) hardening. Moreover, Heterogeneous-3.5 mm/s composite achieves a 108.3% increase in toughness compared with the Uniform-0.75 mm/s composite. It is mainly because coarse grain (CG) bands can capture and blunt cracks, thereby increasing the energy dissipation for crack propagation and improving toughness. In addition, the CG band of the Heterogeneous-3.5 mm/s composite with larger grain size and lower dislocation density is more conducive to obtaining higher strain hardening and superior blunting crack capability. Thus, the increased ductility and toughness of the Heterogeneous-3.5 mm/s composite is more significant than that Heterogeneous-2.5 mm/s composite. %0 journal article %@ %A Fan, L., Zhou, M., Zhang, Y., Dieringa, H., Qian, X., Zeng, Y., Lu, X., Huang, Y., Quan, G. %D 2023 %J Materials Science and Engineering: A %P 144344 %R doi:10.1016/j.msea.2022.144344 %T Achieving high strength and ductility in a heterogeneous bimodal grain structured TiC/AZ61 magnesium nanocomposites via powder metallurgy %U https://doi.org/10.1016/j.msea.2022.144344 %X Heterogeneous TiC/AZ61 nanocomposites, consisting of TiC-rare coarse grain (CG) bands and TiC-rich fine grain (FG) zones, were fabricated to simultaneously improve the strength and ductility of nanoparticles reinforced Mg matrix composites. The fraction of CG bands could be optimized by adjusting the mechanical ball milling time to change the proportion of powders with different morphologies. It was found that composites began to form a heterogeneous bimodal grain (HBG) structure after 12 h ball milling. With further increasing the ball milling time from 12 h to 30 h, the proportion of spherical powder decreased, the volume fraction of CG bands decreased from 48.4% to 11.7%. Excellent comprehensive mechanical properties (ultimate tensile strength: 417 MPa, yield strength: 323 MPa, and elongation: 10.2%) were achieved for the composite with ∼25 vol% CG bands after 20 h of ball milling. Moreover, the HBG-20 h composite had significant additional strengthening at ultimate tensile strength owing to the existence of geometrically necessary dislocations (GNDs) inside the coarse grain bands, which were introduced by mechanical incompatibility between the CG band and FG zone. Such dislocations provided optimum back-stress work hardening at the HBG-20 h composite due to its suitable CG band fraction (∼ 25 vol%), contributing to the high strain-hardening. %0 journal article %@ 1359-6454 %A Ovri, H., Markmann, J., Barthel, J., Kruth, M., Dieringa, H., Lilleodden, E. %D 2023 %J Acta Materialia %P 118550 %R doi:10.1016/j.actamat.2022.118550 %T Mechanistic origin of the enhanced strength and ductility in Mg-rare earth alloys %U https://doi.org/10.1016/j.actamat.2022.118550 %X Magnesium (Mg) alloys with low concentrations of rare earth additions are known to exhibit strengths and ductility that are significantly higher than those obtained in traditional Mg alloys. However, the mechanisms that underlie these improvements are still open to debate. We assessed these mechanism(s) by carrying out in-depth analysis of the deformation behavior in single crystals of pure Mg and a homogenized Mg-0.75 at.% Gd alloy oriented for twinning, pyramidal- and basal-slip. We observed a fivefold increase in basal CRSS, an eightfold increase in twinning CRSS and a fourfold decrease of the pyramidal/basal CRSS (P/B) ratio due to Gd addition. We also observed that while twinning and pyramidal slip activities were similar in the two material systems, basal slip was radically different. Specifically, basal slip was planar in the alloy but wavy in pure Mg. Our work reveals that these observations are a consequence of Gd-rich short-range ordered (SRO) clusters in the alloy. We show that interactions between dislocations and the SRO clusters would lead to significant increases in strength and slip activity, and consequently, ductility improvements in homogenized polycrystalline Mg-Gd alloys. %0 journal article %@ 2079-4991 %A Giannopoulou, D., Bohlen, J., Ben Khalifa, N., Dieringa, H. %D 2022 %J Nanomaterials %N 15 %P 2682 %R doi:10.3390/nano12152682 %T Influence of Extrusion Rate on Microstructure and Mechanical Properties of Magnesium Alloy AM60 and an AM60-Based Metal Matrix Nanocomposite %U https://doi.org/10.3390/nano12152682 15 %X Metal matrix nanocomposites are attracting attention because of their great potential for improved mechanical properties and possible functionalization. These hybrid materials are often produced by casting processes, but they can also develop their property profile after hot working, e.g., by forging or extrusion. In this study, a commercial cast magnesium alloy AM60 was enriched with 1 wt.% AlN nanoparticles and extruded into round bars with varied extrusion rates. The same process was carried out with unreinforced AM60 in order to determine the influences of the AlN nanoparticles in direct comparison. The influence of extrusion speed on the recrystallization behavior as well the effect of nanoparticles on the microstructure evolution and the particle-related strengthening are discussed and assessed with respect to the resulting mechanical performance. %0 journal article %@ 1438-1656 %A You, S., Huang, Y., Dieringa, H., Maawad, E., Gan, W., Zhang, Y., Kainer, K., Willumeit-Römer, R., Hort, N. %D 2022 %J Advanced Engineering Materials %N 4 %P 2101033 %R doi:10.1002/adem.202101033 %T Effects of Y Additions on the Microstructures and Mechanical Behaviours of as Cast Mg–xY–0.5Zr Alloys %U https://doi.org/10.1002/adem.202101033 4 %X Previous investigations demonstrated that rare-earth elements (REs) could improve their creep properties effectively. Herein, the influence of Y content on the creep properties of magnesium is investigated systematically with different amount of Y additions. The mechanisms responsible for creep deformation are clarified by the analysis of stress exponent and microstructural characterizations. It is found that the addition of Y in Mg can improve both the ambient strength and high temperature strength owing to its effective solid solution strengthening. At room temperature, the yield strength of Mg–Y alloys has a linear relation with the content of Y. When tested at high temperatures, the yield strength reduces. Compared with pure magnesium, Mg–Y alloys exhibit a high thermal stability even above 200 °C. Small amount of Y addition can improve the creep resistance of Mg largely. With further increasing its content, its contribution to the improvement of creep resistance is weakened for Mg. Under the applied stresses 60–100 MPa and at temperatures of 200–250 °C, the responsible creep mechanism is dislocation controlled. During creep deformation, the Y segregation regions play an important role in hindering the movement of dislocations. %0 journal article %@ 0921-5093 %A Yang, H., Jiang, B., Huang, G., Huang, Y., Jin, Y., Gavras, S., Dieringa, H. %D 2022 %J Materials Science and Engineering: A %P 142358 %R doi:10.1016/j.msea.2021.142358 %T Revealing the role of Al in the microstructural evolution and creep properties of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn alloy %U https://doi.org/10.1016/j.msea.2021.142358 %X The influence of Al (0.5 wt%, 1 wt%, 2 wt%) on the microstructural evolution and creep resistance of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn (El21) alloy was systematically investigated. The creep results revealed that the additions of 0.5 wt% and 1 wt% Al significantly decreased the creep rate of El21 by more than an order of magnitude, whereas 2 wt% Al in El21 led to the reduction of creep properties. Microstructural analyses indicated that the additions of 0.5 wt% and 1 wt% Al led to significant grain coarsening due to the consumption of Zr via the formation of Al2Zr3 and Al2Zr phases. In contrast, the addition of 2 wt% Al caused distinct grain refinement, resulting from the additional formation of lumpy Al2RE in the centre of α-Mg grains. Additionally, the increase of Al content in the El21 gradually led to the disappearance of the Mg3RE phase and left Al2RE as the only dominant phase. The main Al–Zr phase was also changed from Al2Zr3+Al2Zr to Al2Zr phase. Creep data analysis showed that the dominant creep mechanism was dislocation creep for all alloys, which was in agreement with the EBSD and TEM characterizations. The enhanced creep resistance via the addition of 0.5 wt% and 1 wt% Al was ascribed to the high area fraction of intermetallic phases and the additional formation of the thermally stable Al2RE phase. El21 + 0.5Al has better creep resistance than El21+1Al, which was attributed to its stronger dynamic precipitation strengthening from γ precipitates. The deteriorated creep properties caused by adding 2 wt% Al in El21 alloy arose from the bimodal inhomogeneous distribution of grains and the laminar Al2RE phase. Such microstructure might cause significant stress concentrations and could not effectively impede dislocation motion or reinforce the grain/dendritic boundaries during creep, thus deteriorating the creep properties of El21+2Al. %0 journal article %@ 0267-0836 %A Majhi, J., Mondal, A., Basu, A., Dieringa, H., Kumar, S. %D 2022 %J Materials Science and Technology %N 6 %P 377-389 %R doi:10.1080/02670836.2022.2045546 %T Influence of Ca+Bi on tensile and strain hardening behaviour of AZ91 alloy %U https://doi.org/10.1080/02670836.2022.2045546 6 %X The influence of Ca + Bi on the tensile and strain hardening behaviour of the AZ91 alloy at ambient and elevated temperatures have been examined. The values of YS are higher, and ductility is lower of all the modified alloys. The UTS of the modified AZ91 alloys is lower except at 473 K. The UTS values decrease with an increase in test temperature for all the alloys. The improved YS of the modified alloys is owing to reduced grain size. The brittle Mg3Bi2, Al2Ca and Bi3Ca5 phases in the modified alloys reduce their UTS and ductility. The transgranular cleavage fracture at 298 K changes to quasi-cleavage fracture at 473 K. Several dislocations piled up around the β-Mg17Al12 and Al2Ca phases are seen. %0 journal article %@ 2075-4701 %A Chavez, L., Veleva, L., Sanchez, G., Dieringa, H. %D 2022 %J Metals %N 12 %P 1997 %R doi:10.3390/met12121997 %T AM60-AlN Nanocomposite and AM60 Alloy Corrosion Activity in Simulated Marine-Coastal Ambience %U https://doi.org/10.3390/met12121997 12 %X The initial stages of AM60-AlN nanocomposite and AM60 corrosion behaviors were compared over 30 days of exposure to solution (NaCl, Na2SO4 and NaHCO3), simulating the marine-coastal environment (SME). The incorporation of AlN nanoparticles (1.0 wt.%) in the AM60 alloy matrix favored the lower roughness of the AM60-AlN, associated with the grain refinement in the matrix. During the immersion of the alloys, pH of the SME solution shifted to alkaline values >9, and therefore, the solubility of AlN aluminum hydroxide phases were raised, followed by a slightly higher release of Mg-ions and corrosion rate increase. The chloride ions attributed to the unstability of the Al-Mn phase and Al(OH)3 corrosion product was formed in a low content. The composite AM60-AlN presented lower value of the electrochemical noise resistance (Rn), suggesting that the corrosion process occurs with less difficulty. The localized corrosion near the Al-Mn cathodes seems to be stronger on the composite surface, in area and depth of penetration. The corrosion current fluctuations suggested that the corrosion is a weakly persistent process, dominated by the fractional Gaussian noise (fGn). %0 journal article %@ 2079-4991 %A Şevik, H., Özarslan, S., Dieringa, H. %D 2022 %J Nanomaterials %N 24 %P 4399 %R doi:10.3390/nano12244399 %T Assessment of the Mechanical and Corrosion Properties of Mg-1Zn-0.6Ca/Diamond Nanocomposites for Biomedical Applications %U https://doi.org/10.3390/nano12244399 24 %X In this work, the microstructure, mechanical properties, and corrosion behavior of the Mg-1Zn-0.6Ca matrix alloy (ZX10), reinforced by adding various amounts of nanodiamond particles (0.5, 1, and 2 wt.%), prepared by the ultrasound-assisted stir-casting method, were investigated as they are deemed as potential implant materials in biomedical applications. Microstructure, nanoindentation, mechanical tensile, immersion, and potentiodynamic polarization tests were performed for evaluating the influence of the addition of nanodiamond particles on the alloy’s mechanical and biocorrosion properties. The results revealed that the addition of nanodiamond particles causes a reduction in the alloy’s grain size. The alloy’s nanohardness and elastic modulus values increased when the amount of added nanodiamond particles were increased. The nanocomposite with an addition of 0.5% ND showed the best composition with regard to an acceptable corrosion rate as the corrosion rates are too high with higher additions of 1 or 2% NDs. At the same time, the yield strength, tensile strength, and elongation improved slightly compared to the matrix alloy. %0 journal article %@ 2073-4352 %A Mance, S., Dieringa, H., Bohlen, J., Gavras, S., Stark, A., Schell, N., Pereira da Silva, J., Tolnai, D. %D 2022 %J Crystals %N 11 %P 1502 %R doi:10.3390/cryst12111502 %T In Situ Synchrotron Radiation Diffraction Study of Compression of AZ91 Composites Reinforced with Recycled Carbon Fibres %U https://doi.org/10.3390/cryst12111502 11 %X Lightweight structural materials are increasingly sought after in the automotive and aerospace industries for their potential to improve fuel efficiency. Magnesium-based metal-matrix composites are potential candidates for these kinds of applications. The use of recycled carbon fibres offers further energy and cost savings. The recycled carbon fibre composites were manufactured by stir casting with high-dispersion shearing, then were extruded and subsequently heat treated. The compressive deformation mechanisms of the composites compared to AZ91 were investigated using in situ synchrotron radiation diffraction. An increase in ultimate compressive strength was achieved in the composites compared to AZ91. The deformation mechanisms active in the composites were similar to those in AZ91. Magnesium alloys in compression typically show extensive twinning; this was observed in AZ91 and the AZ91 composites. The stress required for twinning onset was increased in the composites, and the twin volume fraction at failure was decreased compared to AZ91. %0 journal article %@ 2213-9567 %A Kandemir, S., Gavras, S., Dieringa, H. %D 2021 %J Journal of Magnesium and Alloys %N 5 %P 1753-1767 %R doi:10.1016/j.jma.2021.03.029 %T High temperature tensile, compression and creep behavior of recycled short carbon fibre reinforced AZ91 magnesium alloy fabricated by a high shearing dispersion technique %U https://doi.org/10.1016/j.jma.2021.03.029 5 %X The present study seeks the feasibility of using short carbon fibres recycled from polymer matrix composites as alternative to virgin carbon fibres in the reinforcement of magnesium alloys. The microstructures, high temperature mechanical and creep properties of AZ91 alloy and its composites with various recycled carbon fibre contents (2.5 and 5 wt.%) and lengths (100 and 500 μm) were investigated in the temperature range of 25–200 °C. The microstructural characterization showed that the high shear dispersion technique provided the cast composites with finer grains and relatively homogenous distribution of fibres. The materials tested displayed different behaviour depending on the type of loading. In general, while enhancements in the mechanical properties of composites is attributed to the load bearing and grain refinement effects of fibres, the fluctuations in the properties were discussed on the basis of porosity formation, relatively high reinforcement content leading to fibre clustering and interlayer found between the matrix and reinforcement compared to those of AZ91 alloy. The compressive creep tests revealed similar or higher minimum creep rates in the recycled carbon fibre reinforced AZ91 in comparison to the unreinforced AZ91. %0 journal article %@ 2405-4615 %A Yang, H., Patel, J., Yang, X., Gavras, S., Dieringa, H. %D 2021 %J Current Nanomaterials %N 2 %P 106-118 %R doi:10.2174/2405461506666210420133620 %T Properties of Mg-based Metal Matrix Nanocomposites Processed by High Shear Dispersion Technique (HSDT) - A Review %U https://doi.org/10.2174/2405461506666210420133620 2 %X Metal Matrix Nanocomposites (MMNCs) often show excellent properties as compared to their non-reinforced alloys due to either the achieved grain refinement or Orowan strengthening. Especially in light metals such as aluminium and magnesium as the matrix has the potential to be significantly improved in relation to mechanical properties. Functionalisation can also be achieved in some cases. However, the challenge lies in the homogeneous distribution of the ceramic nanoparticles in the melt if MMNCs have been processed via melt metallurgical processes. The large surface area of the nanoparticles generates large van der Waals forces, which need to be overcome. Furthermore, the wettability of the particles with molten metal is difficult. Additional forces can be applied by ultrasound, electromagnetic stirring, or even high-shearing. In this paper, properties of MMNCs with a light metal matrix, which have been produced with the High-Shearing Dispersion Technique are discussed. First, the process with its different characteristics and the underlying theory is presented, and then property improvements are discussed by comparing MMNCs to their matrix materials. %0 journal article %@ 2075-4701 %A Chavez, L., Veleva, L., Feliu, S., Giannopoulou, D., Dieringa, H. %D 2021 %J Metals %N 6 %P 990 %R doi:10.3390/met11060990 %T Corrosion Behavior of Extruded AM60-AlN Metal Matrix Nanocomposite and AM60 Alloy Exposed to Simulated Acid Rain Environment %U https://doi.org/10.3390/met11060990 6 %X The present work compared the initial stages of corrosion process development on the AM60-AlN metal matrix nanocomposite surface and on AM60, during their exposure for 30 days to simulated acid rain solution (SAR). The AlN nanoparticles were observed as “attached” to those of Mn-rich AlMn intermetallic particles, forming clusters. The introduction of 1.0 wt.% AlN (≈ 80 nm) in the AM60 alloy carried a slight grain refinement and favored the formation of a denser and more protective corrosion layer, suggested by the electrochemical impedance spectroscopy (EIS) values of higher charge transfer resistance (R2) and capacitance, characteristic of the double layer in the presence of corrosion products, and also suggested by Rn (EN) values, compared to those of the AM60 alloy. Thus, the concentration of the released Mg-ions from the composite surface was lower. Due to the increase in time of the SAR solution pH, Al de-alloying may occur, as well as Al(OH)3 formation, as confirmed by XPS analysis. Due to the presence of Cl-ions in SAR solution, localized corrosion was observed, suggested as fractional Gaussian noise of a stationary and persistent process in time, according to the PSD of the corrosion current fluctuations (EN). %0 journal article %@ 2296-8016 %A Höche, D., Weber, W., Gazenbiller, E., Gavras, S., Hort, N., Dieringa, H. %D 2021 %J Frontiers in Materials %P 575530 %R doi:10.3389/fmats.2021.575530 %T Novel Magnesium Based Materials: Are They Reliable Drone Construction Materials? A Mini Review %U https://doi.org/10.3389/fmats.2021.575530 %X Novel magnesium-based materials are ideal candidates for use in future aviation vehicles because they are extremely light and can therefore significantly increase the range of these vehicles. They show very good castability, are easy to machine and can be shaped into profiles or forgings to be used as components for next generation aerial vehicle construction. In the case of a large number of identical components, high-pressure die casting of magnesium alloys is clearly superior to high-pressure die casting of aluminum alloys. This is due to the lower solubility of iron in magnesium and thus tool/casting life is significantly longer. In addition, the die filling times for magnesium high-pressure die casting are approximately 30% shorter. This is due to the lower density: aluminum alloys are approximately 50% heavier than magnesium alloys, which is a significant disadvantage for aluminum alloys especially in the aerospace industry. There are cost-effective novel die casting alloys, besides AZ91 or AM50/60 such as DieMag633 or MRI230D, which show very good specific strength at room and elevated temperatures. In the case of magnesium-based wrought alloys, the choice is smaller, a typical representative of these materials is AZ31, but some new alloys based on Mg-Zn-Ca are currently being developed which show improved formability. However, magnesium alloys are susceptible to environmental influences, which can be eliminated by suitable coatings. Novel corrosion protection concepts for classical aerial vehicles currently under development might suitable but may need adaption to the construction constraints or to vehicle dependent exposure scenarios. Within this mini-review a paradigm change due to utilization of new magnesium materials as drone construction material is briefly introduced and future fields of applications within next-generation aerial vehicles, manned or unmanned, are discussed. Possible research topics will be addressed. %0 journal article %@ 1526-6125 %A Shastri, H., Mondal, A., Dutta, K., Dieringa, H., Kumar, S. %D 2020 %J Journal of Manufacturing Processes %P 566-573 %R doi:10.1016/j.jmapro.2020.07.010 %T Microstructural correlation with tensile and creep properties of AZ91 alloy in three casting techniques %U https://doi.org/10.1016/j.jmapro.2020.07.010 %X The relationships among microstructure, tensile and creep behaviour of the AZ91 Mg alloy produced by three different casting techniques have been investigated. All the as-cast alloys consist of primary Mg (α-Mg) and β-Mg17Al12 phases. The volume fraction of β-Mg17Al12 phase is the highest in the gravity casting (GC), intermediate in the squeeze-casting (SC) and the lowest in the high-pressure die-casting (HPDC). The best tensile properties are exhibited by the SC alloy at all the temperatures employed in the present investigation owing to the presence of negligible porosity and relatively finer grain size. Fracture surfaces of the broken tensile specimens reveal the quasi-cleavage fracture. The best and the worst creep resistance are exhibited by the SC and HPDC alloys respectively with the GC alloy exhibiting the intermediate creep resistance. The inferior creep resistance of the HPDC alloy is attributed to the presence of a higher amount of porosity that allows easy crack initiation and growth during creep tests. On the contrary, the negligible porosity and continuous network of eutectic phase contributes to the superior creep resistance of the SC alloy. %0 journal article %@ 0921-5093 %A Yang, H., Zander, D., Jiang, B., Huang, Y., Gavras, S., Kainer, K., Dieringa, H. %D 2020 %J Materials Science and Engineering A %P 139669 %R doi:10.1016/j.msea.2020.139669 %T Effects of heat treatment on the microstructural evolution and creep resistance of Elektron21 alloy and its nanocomposite %U https://doi.org/10.1016/j.msea.2020.139669 %X In previously published research, creep resistance of commercial alloy Elektron21 (El21) and El21 + 1% AlN/Al nanocomposite were predominantly investigated in as-cast condition, little work focused on creep resistance following heat treatment. In this work, El21 and its nanocomposite with and without T6 treatment (520 °C for 8 h and 200 °C for 16 h) were prepared to reveal the influence of heat treatment on their microstructural evolutions and creep properties. Different intermetallic particles and precipitates that formed in El21 and El21 + 1% AlN/Al with different states were characterized using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Creep tests were performed over a stress range of 80–140 MPa at 240 °C. Creep results showed that the application of T6 treatment could improve the creep resistance of El21, but deteriorate that of El21 + 1% AlN/Al. This is attributed to the reduced amount of γ'' and β′ precipitates in El21 + 1% AlN/Al (T6) after ageing, resulting from the formation of plate-like Al2(Nd, Gd) (Al2RE) precipitates. It is also found that after T6 heat treatment, El21 (T6) had a lower minimum creep rate with a shorter duration of secondary creep stage than El21 + 1% AlN/Al (T6) at high creep temperatures due to the overageing of precipitates and the thermal stability of the Al2RE particles. El21 + 1% AlN/Al nanocomposites, either in the as-cast or T6 condition, show a much longer duration of secondary creep than NP-free El21. The responsible mechanism was attributed to the addition of AlN NPs and the formation of particulate/plate Al2RE phase. %0 journal article %@ 0921-5093 %A Mo, N., McCarroll, I., Tan, Q., Ceguerra, A., Cairney, J., Dieringa, H., Huang, Y., Jiang, B., Pan, F., Bermingham, M., Zhang, M.-X. %D 2020 %J Materials Science and Engineering A %P 139152 %R doi:10.1016/j.msea.2020.139152 %T Roles of Nd and Mn in a new creep-resistant magnesium alloy %U https://doi.org/10.1016/j.msea.2020.139152 %X Modification of the recently developed creep-resistant Mg-3Gd-2Ca (wt.%) magnesium alloy using Nd and Mn remarkably improved the creep resistance at both 180 and 210 . The modified Mg-2Gd-1Nd-2Ca-0.5Mn alloy after solid solution treatment exhibited outstanding creep resistance that is superior to the commercial creep-resistant Mg alloy, EV31, but contained less RE addition. The microstructural observations revealed that partial replacement of Gd with 1 wt% Nd did not enhance the effect of dynamic precipitates significantly. But further analysis by atom probe tomography verified the stronger co-segregation between Nd solute atoms and other solute atoms than that of Gd and Ca in the Mg solid solutions, leading to a higher solid solution strengthening effect on the creep resistance. The addition of 0.5 wt% Mn led to the formation of polygonal-shape α-Mn precipitates, which served as heterogeneous nucleants for dynamic precipitates, refining their size and increasing the number densities. As a result, the creep properties of newly developed Mg alloys were strengthened by a combination of improved solid solution strengthening by Nd and increased precipitation hardening by Mn addition. %0 journal article %@ 0921-5093 %A Yang, H., Zander, D., Huang, Y., Kainer, K., Dieringa, H. %D 2020 %J Materials Science and Engineering A %P 139072 %R doi:10.1016/j.msea.2020.139072 %T Individual/synergistic effects of Al and AlN on the microstructural evolution and creep resistance of Elektron21 alloy %U https://doi.org/10.1016/j.msea.2020.139072 %X The creep properties of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn (El21) alloys with additions of 0.25 wt% Al, 0.75 wt% AlN and 1 wt% AlN/Al nanoparticles (NPs) were studied over a stress range from 80 to 140 MPa at 240 °C, respectively. The individual/synergistic roles of Al and AlN in the El21 alloy were investigated systematically to reveal their creep strengthening mechanisms. Creep results show that individually all three additions of 0.25 wt% Al, 0.75 wt% AlN and 1 wt% AlN/Al could increase the creep resistance of El21 alloy apparently. However, the addition of mixed 1 wt% AlN/Al NPs shows the best strengthening effect on creep properties in El21 alloy. Microstructural characterizations reveal that the additions of Al and AlN increased the area fraction of intermetallic particles obviously. Blocky Al2Zr, Al2Zr3 particles and Al2(Nd, Gd) (Al2RE) particulates were observed in both El21 + 0.25% Al and El21 + 0.75%AlN. Nevertheless, when Al and AlN were simultaneously added into El21 alloy the formation of these blocky phases Al2Zr/Al2Zr3 was suppressed, and a larger amount of Al2RE phase was observed. This is attributed to the preferential reaction between AlN and Zr, which restricted the formation of Al–Zr phase and subsequently promoted the reaction of Al-RE phase. The dominant mechanism during creep at 240 °C was calculated to be viscous glide of dislocation. The simultaneous additions of Al and AlN NPs could lead to a more homogeneous distribution of intermetallic particles and increase the amount of Al2RE phase. Such kind of microstructures is beneficial for hindering the dislocation movement, transfer the load from matrix and alleviate the local stress concentration. Consequently, El21 + 1% AlN/Al exhibits the best creep properties among four alloys. %0 journal article %@ 1047-4838 %A You, S., Huang, Y., Dieringa, H., Maawad, E., Gan, W., kainer, K.U., Hort, N. %D 2019 %J JOM: Journal of the Minerals, Metals and Materials Society %N 7 %P 2227-2234 %R doi:10.1007/s11837-019-03515-7 %T The Role of Second Phases on the Creep Behavior of As-Cast and Hot-Extruded Mg-Ca-Zr Alloys %U https://doi.org/10.1007/s11837-019-03515-7 7 %X The effect of second phases on the creep behavior of Mg-Ca-Zr alloys was investigated. Casting and hot-extrusion processes were performed to prepare Mg-xCa-0.5Zr (x = 0 wt.%, 0.3 wt.% and 0.6 wt.%) alloys with different morphologies and distributions of second phases. The as-cast microstructures of Mg-Ca-Zr alloys consisted of an Mg matrix and coarse Mg2Ca intermetallic compounds distributed at the grain boundaries. The hot-extruded microstructures exhibited finer Mg2Ca spherical particles and precipitates distributed homogeneously inside the matrix and along the grain boundaries. The results of creep tests suggested that the viscous glide of dislocation and dislocation climb were the dominant creep mechanisms of Mg-Ca-Zr alloys crept at 200°C. The creep property was strongly related to the morphology and distribution of the Mg2Ca phases. The finer and more homogeneously distributed particles showed a better strengthening effect than the coarser intermetallic compounds distributed along the grain boundaries. %0 journal article %@ 0921-5093 %A Ovri, H., Steglich, D., Dieringa, H., Lilleodden, E.T. %D 2019 %J Materials Science and Engineering A %P 226-234 %R doi:10.1016/j.msea.2018.10.099 %T Grain-scale investigation of the anisotropy of Portevin-Le Chatelier effect in Mg AZ91 alloy %U https://doi.org/10.1016/j.msea.2018.10.099 %X An aspect of Portevin-Le Chatelier (PLC) type plastic instability that is yet to be understood is its orientation dependence. Such knowledge is crucial in view of its implications for texture weakening and, by extension, improvement in formability in Mg–based alloys. In this work, insight into the micromechanisms that govern PLC and its orientation dependence in single grains of Mg AZ91 is achieved using a combination of spherical nanoindentation, local orientation image analysis and crystal plasticity based finite element simulations, which was specifically used to identify the anisotropy in slip activity for the investigated orientations. Moreover, a statistical thermal activation model that is based on the distribution of load jumps between consecutive displacement bursts in the load vs. displacement response is presented. The paper demonstrates the ability of the model to predict the thermal activation parameters for PLC effect. On the basis of the results, we propose a mechanistically sound model for PLC effect that explains the underlying micromechanisms, the role of Al and Zn atoms, and the origin of the orientation dependence of the phenomenon. We also highlight the influence of the PLC effect on formability in Mg–based alloys. %0 journal article %@ 2075-4701 %A Malaki, M., Xu, W., Kasar, A.K., Menezes, P.L., Dieringa, H., Varma, R.S., Gupta, M. %D 2019 %J Metals %N 3 %P 330 %R doi:10.3390/met9030330 %T Advanced Metal Matrix Nanocomposites %U https://doi.org/10.3390/met9030330 3 %X Lightweight high-strength metal matrix nano-composites (MMNCs) can be used in a wide variety of applications, e.g., aerospace, automotive, and biomedical engineering, owing to their sustainability, increased specific strength/stiffness, enhanced elevated temperature strength, improved wear, or corrosion resistance. A metallic matrix, commonly comprising of light aluminum or magnesium alloys, can be significantly strengthened even by very low weight fractions (~1 wt%) of well-dispersed nanoparticles. This review discusses the recent advancements in the fabrication of metal matrix nanocomposites starting with manufacturing routes and different nanoparticles, intricacies of the underlying physics, and the mechanisms of particle dispersion in a particle-metal composite system. Thereafter, the microstructural influences of the nanoparticles on the composite system are outlined and the theory of the strengthening mechanisms is also explained. Finally, microstructural, mechanical, and tribological properties of the selected MMNCs are discussed as well. %0 journal article %@ 0921-5093 %A Yang, H., Huang, Y., Song, B., Kainer, K.U., Dieringa, H. %D 2019 %J Materials Science and Engineering A %P 18-27 %R doi:10.1016/j.msea.2019.03.131 %T Enhancing the creep resistance of AlN/Al nanoparticles reinforced Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn alloy by a high shear dispersion technique %U https://doi.org/10.1016/j.msea.2019.03.131 %X A high shearing dispersion technique (HSDT) was utilized for the first time to incorporate AlN/Al nanoparticles in Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn (Elektron21) alloy. Compressive creep tests of unreinforced and reinforced Elektron21 alloys were performed at 240 °C with an applied stress of between 70-140 MPa. The results show that HSDT is an effective way to incorporate the nanoparticles and therefore to improve the creep resistance of El21 alloy by about one order of magnitude with 0.5% AlN/Al nanoparticles (NPs) compared with unreinforced alloy. The calculation of true creep stress exponent indicates that the viscous glide of dislocation and dislocation climbing are the rate controlling mechanisms during creep deformation. The microstructural observations show that the grains changed from equiaxed to dendritic grains with the addition of NPs by HSDT. Grain refiner Zr in Elektron21 alloy was partly consumed by Al atoms from the nano-powder mixture to form stable compound leading to grain coarsening. After high shearing, AlN NPs are effectively dispersed without any discernible clusters. The eutectic phases of El21 + 0.5AlN/Al composite become less continuous, much thinner, and are more homogeneously distributed in the alloy, which helps to pin the grain boundary sliding and hinder the dislocation movement inside the grain. The existence of AlN NPs is helpful for modifying the morphologies of α-Mg dendrites during solidification and thus resulting in obtaining thinner and hyper-branched eutectic phases in the nanocomposite. As a result, the creep resistance of reinforced alloy is additionally improved. %0 journal article %@ 2075-4701 %A Giannopoulou, D., Dieringa, H., Bohlen, J. %D 2019 %J Metals %N 6 %P 667 %R doi:10.3390/met9060667 %T Influence of AlN Nanoparticle Addition on Microstructure and Mechanical Properties of Extruded Pure Magnesium and an Aluminum-Free Mg-Zn-Y Alloy %U https://doi.org/10.3390/met9060667 6 %X A pure Mg and a ZW0303 alloy metal matrix nanocomposite reinforced with AlN nanoparticles were prepared assisted by mechanical stirring and sonication for deagglomeration of particles. The produced nanocomposites were investigated to determine the influence of the AlN nanoparticles during indirect extrusion on the microstructure and texture development, as well as the resulting hardness and mechanical properties. For pure Mg, grain refinement and hardness increase due to the addition of AlN were revealed in the as-cast and the extruded condition. For ZW0303, the same was found for the as-cast condition. However, contamination of the alloy with Al significantly changes the recrystallization behavior during extrusion. This is directly related to the removal of solute Y due to the formation of intermetallic particles. Particle and grain size effects were distinguished for this alloy. %0 journal article %@ 2193-3383 %A Dieringa, H., Kainer, K.U. %D 2019 %J DIALOG - Materialwissenschaft und Werkstofftechnik %P 18-22 %T Neue kriechbestaendige Magnesiumdruckgusslegierungen frei von Seltenen Erden %U %X %0 journal article %@ 1047-4838 %A Yang, H., Huang, Y., Gavras, S., Kainer, K.U., Hort, N., Dieringa, H. %D 2019 %J JOM: Journal of the Minerals, Metals and Materials Society %N 7 %P 2245-2252 %R doi:10.1007/s11837-019-03499-4 %T Influences of AlN/Al Nanoparticles on the Creep Properties of Elektron21 Prepared by High Shear Dispersion Technology %U https://doi.org/10.1007/s11837-019-03499-4 7 %X Elektron21 (E21) and its composites with additions of 0.25 wt.%, 0.5 wt.%, and 1 wt.% AlN/Al nanoparticles (NPs) were fabricated by a high shear dispersion technology. Their creep properties were investigated over a stress range between 80 MPa and 140 MPa at 240°C. The grain size exhibits an obvious increase with the addition of AlN/Al NPs compared with the monolithic E21 alloy. Increasing the content of AlN/Al NPs leads to a pronounced improvement of creep resistance. Microstructural analysis shows that, with the addition of 1% AlN/Al NPs in E21, the distribution of the intermetallics Mg3RE becomes much more homogeneous and their size is reduced. Such Mg3RE particles can prevent the dislocation slip more efficiently during creep. Besides these Mg3RE particles, the additional formation of Al2RE and Al2Zr3 phases, which results from the reactions of AlN/Al NPs and the alloying elements Zr and REs, could act as thermal stable particles to improve the creep resistance. Finally, the remained AlN NPs without reactions are beneficial for the improvement of the creep resistance to some extent due to Orowan strengthening. %0 journal article %@ 0921-5093 %A Yang, H., Huang, Y., Tolnai, D., Kainer, K.U., Dieringa, H. %D 2019 %J Materials Science and Engineering A %P 138215 %R doi:10.1016/j.msea.2019.138215 %T Influences of Al and high shearing dispersion technique on the microstructure and creep resistance of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn alloy %U https://doi.org/10.1016/j.msea.2019.138215 %X Effects of 0.25% Al addition and the high shearing dispersion technique (HSDT) on the microstructure and creep resistance of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn (Elektron21, El21) alloy were investigated. Compressive creep testes were performed at 240 °C over a stress range between 80 and 140 MPa. The results indicate that the creep resistance of El21 was significantly improved by about one order of magnitude with the addition of 0.25% Al and HSDT than that of El21 without Al and HSDT. Microstructural characterizations show that the grains were coarsened from 80.1 ± 5.0 to 167.0 ± 5.7 μm due to the loss of grain refiner Zr by the chemical reaction of Al with Zr. With the addition of 0.25% Al to El21, the grain morphology was changed from equiaxed to typical dendrite. The morphology of intermetallic Mg3RE was modified from network to a pronounced dendritic structure. Owing to the employment of HSDT, the dendrite arm spacing of primary α-Mg was refined from 74.0 ± 6.4 to 56.2 ± 1.6 μm in Al-containing El21 alloy, the dominant Al–Zr compound changed from Al2Zr3 to Al2Zr phase. A small amount of Al2Nd phase was formed. Creep data analysis indicates that the dominant controlling mechanism for H-El21A alloy is dislocation climb during creep deformation. Its superior creep resistance was mainly attributed to the pronounced and dense dendritic structure of Mg3RE intermetallic in the α-Mg hindering the grain boundary sliding and dislocation movement. In addition, the relative homogeneous dispersion of Al2Zr phase and Al2Nd phase with a high melting point can also act as efficient reinforcements to inhibit the dislocation movement and benefit the creep properties. %0 journal article %@ 2296-8016 %A Gavras, S., Zhu, S., Easton, M.A., Gibson, M.A., Dieringa, H. %D 2019 %J Frontiers in Materials %P 262 %R doi:10.3389/fmats.2019.00262 %T Compressive creep behaviour of high-pressure die-cast aluminium-containing magnesium alloys developed for elevated temperature applications %U https://doi.org/10.3389/fmats.2019.00262 %X In addition to AZ- and AM-series magnesium alloys, which are mainly used at ambient temperature, there are also die-cast magnesium alloys developed for use at elevated temperatures. This paper examines the compressive creep resistance of several aluminum-containing magnesium high-pressure die-cast alloys, including the commercially available AE42, AE44-2, AE44-4, MRI230D alloys and newly developed DieMag series, i.e., DieMag211, DieMag422, and DieMag633. Compressive creep is the common load case for automotive powertrain components such as transmission housings, engine blocks or oil pans, which are typically mounted with steel or aluminum bolts that have lower thermal expansion than magnesium alloys. When the components heat up, there is a compressive load in the area around the bolt. The compressive creep experiments are accompanied by microstructure investigations. It is shown that MRI230D and the two high-concentrated DieMag alloys have the best creep resistance at 200°C. Similar results are also observed in the tensile tests at room temperature and 150°C, with DieMag633 showing outstanding strength. %0 journal article %@ 1359-6454 %A Mo, N., McCarroll, I., Tan, Q., Ceguerra, A., Liu, Y., Cairney, J., Dieringa, H., Huang, Y., Jiang, B., Pan, F., Bermingham, M., Zhang, M.-X. %D 2019 %J Acta Materialia %P 185-199 %R doi:10.1016/j.actamat.2019.09.058 %T Understanding solid solution strengthening at elevated temperatures in a creep-resistant Mg–Gd–Ca alloy %U https://doi.org/10.1016/j.actamat.2019.09.058 %X The present work studies the strengthening mechanisms of a creep-resistant Mg-0.5Gd-1.2Ca (at.%) alloy at both room and elevated temperatures. Although peak-ageing (T6) at 180 °C for 32 h led to a significant increase in room temperature strength due to the precipitation strengthening by three types of precipitates (Mg2Ca, Mg5Gd on prismatic planes and a new type of Mg–Gd–Ca intermetallic compound on the basal plane), the as-solid solution treated (T4) alloy exhibited better resistance to temperature softening during compression and to stress relaxation at 180 °C and better creep resistance at 210 °C/100 MPa. The Gd–Ca co-clusters with short-range order in the Mg solid solution, which was verified, at the first time, by atom probe tomography (APT) analysis and atomic-resolution high angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), were responsible for the solid solution hardening, offering a more effective strengthening effect through local order-strengthening. Such solid solution strengthening increased the thermal stability of the alloy structure at elevated temperatures, at least at early stage of the creep. Subsequently, dynamic precipitation started contributing to the creep resistance due to the formation of higher density of precipitates. However, in the T6 alloy, creep testing at elevated temperatures, particularly at 210 °C that was higher than the ageing temperature, led to coarsening of the precipitates, which acted as over ageing. As a result of such over ageing, the resistance of the T6 alloy to heat-induced softening was weakened, leading to lower creep resistance than the T4 alloy. %0 journal article %@ 1059-9495 %A Dmitruk, A., Naplocha, K., Zak, A., Strojny-Nedza, A., Dieringa, H., Kainer, K.U. %D 2019 %J Journal of Materials Engineering and Performance %N 10 %P 6248-6257 %R doi:10.1007/s11665-019-04390-8 %T Development of Pore-Free Ti-Si-C MAX/Al-Si Composite Materials Manufactured by Squeeze Casting Infiltration %U https://doi.org/10.1007/s11665-019-04390-8 10 %X Open-porous MAX phase skeletons from Ti3SiC2 were manufactured by Microwave-Assisted Self-propagating High-temperature Synthesis (MASHS) and subsequently subjected to squeeze casting infiltration with an Al-Si lightweight casting alloy (EN AC-44200). This alloy was chosen due to its high flowability, corrosion resistance and good machinability. The manufactured composites, together with a reference sample of the original alloy, underwent testing of thermal properties, including thermal conductivity and diffusivity, specific heat and thermal expansion in the temperature range 50-500 °C, which corresponds to the expected working temperatures of the material. The fabricated AlSi/Ti3SiC2 composites have significantly increased thermal stability, with coefficients of thermal expansion (approximately 10-11 × 10−6 °C−1) half that of the original alloy. As regards mechanical properties, the instrumental Young’s modulus and Vickers hardness of the composite materials are 170.8 and 8.5 GPa, respectively. Moreover, the microstructure and phase composition, structural defects and potential impacts between constituents of the manufactured composites were characterized using SEM, TEM and STEM microscopy and EDS and XRD analysis. %0 journal article %@ 2075-4701 %A Dieringa, H. %D 2018 %J Metals %N 6 %P 431 %R doi:10.3390/met8060431 %T Processing of Magnesium-Based Metal Matrix Nanocomposites by Ultrasound-Assisted Particle Dispersion: A Review %U https://doi.org/10.3390/met8060431 6 %X Magnesium-based metal matrix nanocomposites (MMNCs) are an important topic in the development of lightweight structural materials, because their optimized properties are of great interest to the automotive and aerospace industries. Moreover, components with functional properties will also be manufactured from Mg-MMNCs in the future. With a large surface to volume ratio, nanoparticles in the magnesium matrix have an immense effect on mechanical properties, even at low concentrations. The mechanical properties of these materials can be tailored using ceramic nanoparticles, which have been available at a very low cost for a number of years. However, the particle concentration, chemical composition, particle size, and process parameters must be attuned to the respective alloy, in order to influence the resulting properties. When using very small particles, a major problem is to homogeneously distribute the particles in the melt. Due to their large surface area, strong van der Waals forces act to hold the particles together in clusters. At the same time, wettability of the particles with a magnesium melt is very poor. Ultrasonic stirring processes have proven their effectiveness in the de-agglomeration and dispersion of nanoparticles. This review presents ultrasound-assisted processes for the production of these materials and describes some properties of the resulting Mg-MMNCs. %0 journal article %@ 1059-9495 %A Suresh, K., Rao, K.P., Chalasani, D., Krishna, P.Y.V.R., Hort, N., Dieringa, H. %D 2018 %J Journal of Materials Engineering and Performance %N 3 %P 1440-1449 %R doi:10.1007/s11665-018-3219-8 %T Deformation Mechanisms and Formability Window for As-Cast Mg-6Al-2Ca-1Sn-0.3Sr Alloy (MRI 230D) %U https://doi.org/10.1007/s11665-018-3219-8 3 %X The hot deformation characteristics of MRI 230D alloy have been evaluated in the temperature range 260-500 °C and strain rate range 0.0003-10 s−1, on the basis of processing map. The processing map exhibited two domains in the ranges: (1) 300-370 °C and 0.0003-0.001 s−1 and (2) 370-480 °C and 0.0003-0.1 s−1. Dynamic recrystallization occurs in the both domains with basal slip dominating in the first domain along with climb as recovery process and second-order pyramidal slip dominating in the second with the recovery by cross-slip. In Domains (1) and (2), the apparent activation energy values estimated using the kinetic rate equation are 143 and 206 kJ/mole, respectively, the first one being close to that for lattice self-diffusion confirming climb. It is recommended that the alloy is best processed at 450 °C and strain rates less than 0.1 s−1, where non-basal slip and cross-slip occur extensively to impart excellent workability. The alloy exhibits flow instability in the form of adiabatic shear band formation and flow localization at lower temperatures and higher strain rates. Forging of a cup-shaped component was performed under various conditions, and the results validated the predictions of the processing map on the workability domains as well as the instability regimes. %0 journal article %@ 1438-1656 %A Rao, K.P., Prasad, Y.V.R.K., Dharmendra, C., Suresh, K., Hort, N., Dieringa, H. %D 2018 %J Advanced Engineering Materials %N 9 %P 1701102 %R doi:10.1002/adem.201701102 %T Review on Hot Working Behavior and Strength of Calcium-Containing Magnesium Alloys %U https://doi.org/10.1002/adem.201701102 9 %X In recent years, calcium has been a chosen alloying element as an alternative to rare‐earth elements for developing creep‐resistant magnesium alloys, which find promising applications for components in automobile and aerospace industries, and as bio‐implants. In this paper, the research covering the influence of Ca additions to several magnesium alloy systems on their strength, microstructure, and hot workability is reviewed. During mechanical processing, the formation of basal texture is considerably weakened by Ca addition. Ca‐containing alloys have limited workability and can be processed only by choosing the right combination of temperature and strain rate that corresponds to the occurrence of dynamic recrystallization (DRX). This can be done without trial‐and‐error through the use of processing maps. The processing maps for hot working of low‐Ca containing alloys typically exhibit three DRX domains while the maps for high‐Ca alloys typically exhibit only two DRX domains. In particular, the high‐Ca alloys have to be processed at lower strain rates and higher temperatures since the high volume content of intermetallic particles prevents DRX at high strain rates. Flow instabilities occur rampantly in Ca‐containing alloys, particularly in high‐Ca alloys, at lower temperatures and higher strain rates that have to be avoided during their thermo‐mechanical processing. %0 journal article %@ 0261-3069 %A Mo, N., Tan, Q., Bermingham, M., Huang, Y., Dieringa, H., Hort, N., Zhang, M.-X. %D 2018 %J Materials and Design %P 422-442 %R doi:10.1016/j.matdes.2018.06.032 %T Current development of creep-resistant magnesium cast alloys: A review %U https://doi.org/10.1016/j.matdes.2018.06.032 %X The low creep resistance has been one of the major issues of Mg alloys, which limited their wider industrial applications in the past decades. It has been reported that the inherent creep resistance of Mg should be higher than that Al. Hence, it is highly likely that the low creep resistance of Mg alloys was attributed to the effects of alloying elements rather than Mg itself. In order to systematically understand the effects of alloying elements on the creep behaviours of cast Mg alloys and therefore to develop new alloys with higher creep resistance, the present work reviews the major creep-resistant Mg systems that were developed and successfully commercialized for applications at different temperatures. Because the majority of commercial Mg alloys are used as cast, this review focuses on cast alloys. %0 journal article %@ 2075-4701 %A Rao, K.P., Chalasani, D., Suresh, K., Prasad, Y.V.R.K., Dieringa, H., Hort, N. %D 2018 %J Metals %N 6 %P 463 %R doi:10.3390/met8060463 %T Connected Process Design for Hot Working of a Creep-Resistant Mg–4Al–2Ba–2Ca Alloy (ABaX422) %U https://doi.org/10.3390/met8060463 6 %X With a view to design connected processing steps for the manufacturing of components, the hot working behavior of the ABaX422 alloy has been characterized for the as-cast and extruded conditions. In the as-cast condition, the alloy has a limited workability, due to the presence of a large volume of intermetallic phases at the grain boundaries, and is not suitable to process at high speeds. A connected processing step has been designed on the basis of the results of the processing map for the as-cast alloy, and this step involves the extrusion of the cast billet to obtain a 12 mm diameter rod product at a billet temperature of 390 °C and at a ram speed of 1 mm s−1. The microstructure of the extruded rod has a finer grain size, with redistributed fine particles of the intermetallic phases. The processing map of the extruded rod exhibited two new domains, and the one in the temperature range 360–420 °C and strain rate range 0.2–10 s−1 is useful for manufacturing at high speeds, while the lower temperature develops a finer grain size in the product to improve the room temperature strength and ductility. The area of the flow instability is also reduced by the extrusion step, widening the workability window. %0 journal article %@ 1438-1656 %A Kucharczyk, A., Naplocha, K., Kaczmar, J.W., Dieringa, H., Kainer, K.U. %D 2018 %J Advanced Engineering Materials %N 1 %P 1700562 %R doi:10.1002/adem.201700562 %T Current Status and Recent Developments in Porous Magnesium Fabrication %U https://doi.org/10.1002/adem.201700562 1 %X A significant number of studies have been dedicated to the fabrication and properties of metallic foams. The most recent research is focused on metals with low weight and good mechanical properties, such as titanium, aluminum, and magnesium. Whereas the first two are already fairly well studied and already find application in industry, magnesium currently remains at the research stage. The present review covers the studies conducted on fabrication techniques, surface modifications, and properties of porous structures made of magnesium and its alloys. %0 journal article %@ 1003-6326 %A Suresh, K., Rao, K.P., Prasad, Y.V.R.K., Hort, N., Dieringa, H. %D 2018 %J Transactions of Nonferrous Metals Society of China %N 8 %P 1495-1503 %R doi:10.1016/S1003-6326(18)64790-9 %T Hot forging of Mg-4Al-2Ba-2Ca (ABaX422) alloy and validation of processing map %U https://doi.org/10.1016/S1003-6326(18)64790-9 8 %X A cup-shaped component of Mg-4Al-2Ba-2Ca (ABaX422) alloy was forged in the temperature range of 300–500 °C and at speeds in the range of 0.01–10 mm/s with a view to validate the processing map and study the microstructural development. The process was simulated through finite-element method to estimate the local and average strain rate ranges in the forging envelope. The processing map exhibited two domains in the following ranges: (1) 300–390 °C and 0.0003–0.001 s−1, and (2) 400–500 °C and 0.0003–0.3 s−1 and both represented dynamic recrystallization (DRX). The map revealed a wide flow instability regime at higher strain rates and temperatures lower than 400 °C, in which flow localization occurred. Forgings produced under conditions of the above two domains were sound and symmetrical, and had finer grain sizes when being forged in the first domain. However, when being forged in the flow instability regimes, the alloy fractured before the final shape was reached. The experimental load–stroke curves for the conditions within the domains correlated well with the simulated ones, whereas the curves obtained in the instability regime were uneven. %0 journal article %@ 0360-3199 %A Hardian, R., Pistidda, C., Chaudhary, A.-L., Capurso, G., Gizer, G., Cao, H., Milanese, C., Girella, A., Santoru, A., Yigit, D., Dieringa, H., Kainer, K.U., Klassen, T., Dornheim, M. %D 2018 %J International Journal of Hydrogen Energy %N 34 %P 16738-16748 %R doi:10.1016/j.ijhydene.2017.12.014 %T Waste Mg-Al based alloys for hydrogen storage %U https://doi.org/10.1016/j.ijhydene.2017.12.014 34 %X Magnesium has been studied as a potential hydrogen storage material for several decades because of its relatively high hydrogen storage capacity, fast sorption kinetics (when doped with transition metal based additives), and abundance. This research aims to study the possibility to use waste magnesium alloys to produce good quality MgH2. The production costs of hydrogen storage materials is still one of the major barriers disabling scale up for mobile or stationary application. The recycling of magnesium-based waste to produce magnesium hydride will significantly contribute to the cost reduction of this material. This study focuses on the effect of different parameters such as the addition of graphite and/or Nb2O5 as well as the effect of milling time on the material hydrogenation/de-hydrogenation performances. In addition, morphology and microstructural features are also evaluated for all the investigated materials. %0 journal article %@ 0921-5093 %A Daudin, R., Terzi, S., Mallmann, C., Sanchez Martin, R., Lhuissier, P., Boller, E., Pacureanu, A., Katsarou, L., Dieringa, H., Salvo, L. %D 2017 %J Materials Science and Engineering A %P 76-82 %R doi:10.1016/j.msea.2017.01.103 %T Indirect improvement of high temperature mechanical properties of a Mg-based alloy Elektron21 by addition of AlN nanoparticles %U https://doi.org/10.1016/j.msea.2017.01.103 %X Magnesium being the lightest metal on earth used as a structural material, the design of the chemistry and the microstructures of Mg-based alloys has been developed over the years to always further ameliorate their mechanical properties. A supplementary option consists in adding ceramic nanoparticles to such alloys to design Mg-based metal matrix nanocomposites (MMNCs) displaying improvement of both strength and ductility. In practice however, careful attention is required to understand the fundamental mechanisms at the heart of the enhancement of these properties as they still remain quite uncertain and subjected to misleading interpretations. Here, high temperature (350 °C) strain rate jump tests in compression reveal an enhancement of 20–60% of the mechanical properties when AlN nano-particles are added to the Elektron21 alloy (Mg-2.8Nd-1.2Gd-0.4Zr-0.3Zn, in wt%). At the same time, nano-indentation investigations suppose that forest or Orowan strengthening, due to particles-dislocations interactions, is unlikely to occur. Instead, using complementary microstructural characterization techniques (scanning electron macroscopy, energy dispersive spectroscopy as well as micro- and nano-tomography), we show that AlN nano-particles physically and chemically interact with the alloy and modify the overall microstructure, in particular the intermetallic phase, at the origin of the improvement of the mechanical properties. %0 journal article %@ 1013-9826 %A Rao, K.P., Bagheripoor, M., Dieringa, H., Hort, N. %D 2017 %J Key Engineering Materials, Advances in Engineering Plasticity and its Application XIII %P 232-237 %R doi:10.4028/www.scientific.net/KEM.725.232 %T High Temperature Deformation of Cast ZW11 Magnesium Alloy with Very Large Grain Size %U https://doi.org/10.4028/www.scientific.net/KEM.725.232 %X instability. The microstructures of the deformed alloy provided support to the processing map. %0 journal article %@ 2075-4701 %A Dieringa, H. %D 2017 %J Metals %N 2 %P 38 %R doi:10.3390/met7020038 %T Influence of Cryogenic Temperatures on the Microstructure and Mechanical Properties of Magnesium Alloys: A Review %U https://doi.org/10.3390/met7020038 2 %X Magnesium alloys have been used in the automotive industry and 3C (computer, communication, and consumer electronics) for many years. Their room temperature properties combined with their low density offer a wide range of applications, especially when processed by High Pressure Die Casting (HPDC). The use of magnesium alloys at higher temperatures is well-studied; special creep resistant alloys containing the rare earth elements silver or yttrium are needed. However, when it comes to very low temperatures, only a few studies have been performed to determine the property-microstructure relationship. The possible fields of application at low temperatures are aerospace and satellite parts and tanks for liquefied gases. This review shall not only examine mechanical properties at low temperatures, but also the permanent effects of cyclic or long-lasting cryogenic treatment on the microstructure and mechanical properties. It was found that cryogenic treatment is able to influence the precipitate concentration and grain orientation in some magnesium alloys. Reduction in the number of brittle phases is improving ductility in some cases. It is well-known that high speed tool steels, in particular, can be influenced by cryogenic treatment. Whether this is possible with magnesium alloys and what the mechanisms are shall be reviewed. %0 journal article %@ 2075-4701 %A Dieringa, H., Katsarou, L., Buzolin, R., Szakacs, G., Horstmann, M., Wolff, M., Mendis, C., Vorozhtsov, S., John, D.St. %D 2017 %J Metals %N 10 %P 388 %R doi:10.3390/met7100388 %T Ultrasound Assisted Casting of an AM60 Based Metal Matrix Nanocomposite, Its Properties, and Recyclability %U https://doi.org/10.3390/met7100388 10 %X An AM60 magnesium alloy nanocomposite reinforced with 1 wt % of AlN nanoparticles was prepared using an ultrasound (US) assisted permanent-mould indirect-chill casting process. Ultrasonically generated cavitation and acoustic streaming promoted de-agglomeration of particle clusters and distributed the particles throughout the melt. Significant grain refinement due to nucleation on the AlN nanoparticles was accompanied by an exceptional improvement in properties: yield strength increased by 103%, ultimate tensile strength by 115%, and ductility by 140%. Although good grain refinement was observed, the large nucleation undercooling of 14 K limits further refinement because nucleation is prevented by the formation of a nucleation-free zone around each grain. To assess the industrial applicability and recyclability of the nanocomposite material in various casting processes, tests were performed to determine the effect of remelting on the microstructure. With each remelting, a small percentage of effective AlN nanoparticles was lost, and some grain growth was observed. However, even after the third remelting, excellent strength and ductility was retained. According to strengthening models, enhanced yield strength is mainly attributed to Hall-Petch strengthening caused by the refined grain size. A small additional contribution to strengthening is attributed to Orowan strengthening. %0 journal article %@ 2075-4701 %A Suresh, K., Rao, K.P., Prasad, Y.V.R.K., Wu, C.-M., Hort, N., Dieringa, H. %D 2017 %J Metals %N 12 %P 539 %R doi:10.3390/met7120539 %T Mechanism of Dynamic Recrystallization and Evolution of Texture in the Hot Working Domains of the Processing Map for Mg-4Al-2Ba-2Ca Alloy %U https://doi.org/10.3390/met7120539 12 %X The occurrence of dynamic recrystallization (DRX) and its effect on the evolution of texture during uniaxial compression of a creep-resistant cast Mg-4Al-2Ba-2Ca alloy in the temperature range of 260–500 °C and strain rate range of 0.0003–10 s−1 has been studied using transmission electron microscopy and electron backscatter diffraction techniques with a view to understand its mechanism. For this purpose, a processing map has been developed for this alloy, which revealed two domains of DRX in the temperature and strain rate ranges of: (1) 300–390 °C/0.0003–0.001 s−1 and (2) 400–500 °C/0.0003–0.5 s−1. In Domain 1, DRX occurs by basal slip and recovery by dislocation climb, as indicated by the presence of planar slip bands and high dislocation density leading to tilt boundary formation and a low-intensity basal texture. On the other hand, DRX in Domain 2 occurs by second order pyramidal slip and recovery by cross-slip since the microstructure revealed tangled dislocation structure with twist boundaries and randomized texture. The high volume content of intermetallic phases Mg21Al3Ba2 and (Al,Mg)2Ca eutectic phase is considered to be responsible for the observed hot deformation behavior. %0 journal article %@ 2075-4701 %A Rao, K.P., Suresh, K., Prasad, Y.V.R.K., Dharmendra, C., Hort, N., Dieringa, H. %D 2017 %J Metals %N 10 %P 405 %R doi:10.3390/met7100405 %T High Temperature Strength and Hot Working Technology for As-Cast Mg–1Zn–1Ca (ZX11) Alloy %U https://doi.org/10.3390/met7100405 10 %X Cast Mg–1Zn–1Ca alloy (ZX11) has been tested to evaluate its compressive strength between 25 °C and 250 °C, and workability in the range of 260–500 °C. The ultimate compressive strength of this alloy is about 30% higher than that of creep-resistant alloy Mg–3Sn–2Ca (TX32) between 25 °C and 200 °C, and exhibits a plateau between 100 °C and 175 °C, similar to TX32. This is attributed to Mg2Ca particles present at grain boundaries that reduce their sliding. The processing map, developed between 260 and 420 °C in the strain rate limits of 0.0003 s−1 to 1 s−1, exhibited two domains in the ranges: (1) 280–330 °C and 0.0003–0.01 s−1 and (2) 330–400 °C and 0.0003–0.1 s−1. In these domains, dynamic recrystallization occurs, with basal slip dominating in the first domain and prismatic slip in the second, while the recovery mechanism being climb of edge dislocations in both. The activation energy estimated using standard kinetic rate equation is 191 kJ/mol, which is higher than the value for lattice self-diffusion in magnesium indicating that a large back stress is created by the presence of Ca2Mg6Zn3 intermetallic particles in the matrix. It is recommended that the alloy be best processed at 380 °C and 0.1 s−1 at which prismatic slip is favored due to Zn addition. At higher strain rates, the alloy exhibits flow instability and adiabatic shear band formation at <340 °C while flow localization and cracking at grain boundaries occurs at temperatures >400 °C. %0 journal article %@ 2075-4701 %A Rao, K.P., Dharmendra, C., Prasad, Y.V.R.K., Hort, N., Dieringa, H. %D 2017 %J Metals %N 11 %P 513 %R doi:10.3390/met7110513 %T Optimization of Thermo-Mechanical Processing for Forging of Newly Developed Creep-Resistant Magnesium Alloy ABaX633 %U https://doi.org/10.3390/met7110513 11 %X The compressive strength and creep resistance of cast Mg-6Al-3Ba-3Ca (ABaX633) alloy has been measured in the temperature range of 25 to 250 °C, and compared with that of its predecessor ABaX422. The alloy is stronger and more creep-resistant than ABaX422, and exhibits only a small decrease of yield stress with temperature. The higher strength of ABaX633 is attributed to a larger volume fraction of intermetallic particles (Al, Mg)2Ca and Mg21Al3Ba2 in its microstructure. Hot deformation mechanisms in ABaX633 have been characterized by developing a processing map in the temperature and strain rate ranges of 300 to 500 °C and 0.0003 to 10 s−1. The processing map exhibits two workability domains in the temperature and strain rate ranges of: (1) 380 to 475 °C and 0.0003 to 0.003 s−1, and (2) 480–500 °C and 0.003 to 0.5 s−1. The apparent activation energy values estimated in the above two domains (204 and 216 kJ/mol) are higher than that for lattice self-diffusion of Mg, which is attributed to the large back-stress that is caused by the intermetallic particles. Optimum condition for bulk working is 500 °C and 0.01 s−1 at which hot workability will be maximum. Flow instability is exhibited at lower temperatures and higher strain rates, as well as at higher temperatures and higher strain rates. The predictions of the processing map on the workability domains, as well as the instability regimes are fully validated by the forging of a rib-web (cup) shaped component under optimized conditions. %0 journal article %@ 1996-1944 %A Saboori, A., Papovano, E., Pavese, M., Dieringa, H., Badini, C. %D 2017 %J Materials %N 12 %P 1380 %R doi:10.3390/ma10121380 %T Effect of Solution Treatment on Precipitation Behaviors, Age Hardening Response and Creep Properties of Elektron21 Alloy Reinforced by AlN Nanoparticles %U https://doi.org/10.3390/ma10121380 12 %X In the present study, the solution and ageing treatments behavior of Mg-RE-Zr-Zn alloy (Elektron21) and its nano-AlN reinforced nanocomposites have been evaluated. The properties of the thermal-treated materials were investigated in terms of Vickers hardness, the area fraction of precipitates, microstructure and phase composition. The solution treatments were performed by treating at 520 °C, 550 °C and 580 °C in argon atmosphere. The outcomes show that the hardness of the solutionized alloys was slightly affected by the solution temperature. X-ray diffraction and image analysis revealed that the complete dissolution of precipitates was not possible, neither for Elektron21 (El21) nor for its AlN containing nanocomposites. The ageing treatment of El21 led to a significant improvement in hardness after 20 h, while for longer times, it progressively decreased. The effect of ageing on the hardness of El21–AlN composites was found to be much less than this effect on the hardness of the host alloy. Electron backscatter diffraction (EBSD) analysis of El21 and El21–1%AlN after solution treatment confirm the random orientation of grains with a typical texture of random distribution. The as-cast creep results showed that the incorporation of nanoparticles could effectively improve the creep properties, while the results after solution treatment at 520 °C for 12 h followed by ageing treatment at 200 °C for 20 h confirmed that the minimum creep rate of T6-El21 was almost equal to the as-cast El21–AlN. %0 journal article %@ 0921-5093 %A Bankoti, A.K.S., Mondal, A.K., Dieringa, H., Ray, B.C., Kumar, S. %D 2016 %J Materials Science and Engineering A %P 332-345 %R doi:10.1016/j.msea.2016.07.087 %T Impression creep behaviour of squeeze-cast Ca and Sb added AZ91 magnesium alloy %U https://doi.org/10.1016/j.msea.2016.07.087 %X Impression creep technique has been employed to investigate creep behaviour of the squeeze-cast AZ91 Mg alloy modified by the addition of Ca and/or Sb. All the modified alloys exhibit superior creep resistance than the base AZ91 alloy. The combined additions of Ca and Sb are more effective in improving creep resistance than the individual additions. Individual Ca added AZX911 results superior creep resistance than the Sb added AZY911 owing to the higher thermal stability of the Al2Ca phase in the former alloy compared to that of the Mg3Sb2 phase in the later one. The AZXY9120 alloy pertaining 2.0Ca and 0.3Sb (wt%) exhibits the best creep resistance due to reduced amount of β-Mg17Al12 phase and presence of higher amount of dense network of thermally stable Al2Ca phase at grain boundaries. Post creep microstructural observation confirms the ability of the Al2Ca phase to withstand applied high stresses at elevated temperature without undergoing significant changes in its structure. The values of stress exponents and activation energies are in the range of 4.3–6.5 and 111.9±1.1 to 114.9±3.0 kJ/mol, which concludes dislocation climb controlled by pipe diffusion is the dominant creep mechanism for all the alloys in the temperature and stress level employed. %0 journal article %@ 0921-5093 %A Srinivasan, A., Dieringa, H., Mendis, C.L., Huang, Y., Rajesh Kumar, R., Kainer, K.U., Hort, N. %D 2016 %J Materials Science and Engineering A %P 158-167 %R doi:10.1016/j.msea.2015.09.113 %T Creep behavior of Mg–10Gd–xZn (x=2 and 6wt%) alloys %U https://doi.org/10.1016/j.msea.2015.09.113 %X Creep behavior of Mg–10Gd–xZn alloys was investigated with two Zn contents, 2 and 6 wt%. The as cast microstructure of alloys contained (Mg, Zn)3Gd phase at the interdendritic regions and long period stacking ordered (LPSO) phase in the matrix. Increase in the Zn content from 2% to 6%, increased the volume fraction and morphology of second phase [(Mg,Zn)3Gd]. Creep testing at 250 and 300 °C with stress levels between 50 and 120 MPa indicated that increase in Zn content or temperature reduced the creep performance of the Mg–10Gd–xZn alloys. The minimum creep rate of Mg–10Gd–2Zn was one order less that of Mg–10Gd–6Zn. Dynamic precipitation was found in both the alloys during creep deformation at 250 °C and strengthened the alloys: prismatic platelets (Mg5Gd) were observed perpendicular to the LPSO phase in Mg–10Gd–2Zn alloy whereas basal oval precipitates (ternary composition) parallel to the LPSO occurred in Mg–10Gd–6Zn alloy. The dynamic precipitates were not observed in alloys during creep at 300 °C. Ternary bulk precipitates at the LPSO phase was observed in both alloys and at all testing conditions which facilitated the cracking during deformation. More continuous second phase at the interdendritic boundaries facilitated easy cracking in Mg–10Gd–6Zn alloy and hence reduced the creep performance. %0 journal article %@ 0937-4167 %A Dieringa, H., Bohlen, J. %D 2016 %J Konstruktionspraxis : Alles, was der Konstrukteur braucht %P 24-25 %T Magnesiumlegierungen im Leichtbau %U %X Magnesium ist der leichteste metallische Konstruktionswerkstoff. Seine Legierungen haben jedoch einen geringen Marktanteil. Aktuelle Forschungen sollen das ändern. %0 journal article %@ 0142-1123 %A Wittke, P., Klein, M., Dieringa, H., Walther, F. %D 2016 %J International Journal of Fatigue %N 1 %P 59-65 %R doi:10.1016/j.ijfatigue.2015.04.001 %T Corrosion fatigue assessment of creep-resistant magnesium alloy Mg–4Al–2Ba–2Ca in aqueous sodium chloride solution %U https://doi.org/10.1016/j.ijfatigue.2015.04.001 1 %X Low corrosion resistance of magnesium alloys strongly limits their application range. This study aims at the investigation of corrosion influence on microstructure and depending mechanical properties of newly developed magnesium alloy Mg–4Al–2Ba–2Ca. The fatigue properties of this creep-resistant magnesium alloy were investigated under three corrosive environments: double distilled water, 0.01 and 0.1 mol L−1 NaCl solutions. Potentiodynamic polarization measurements and immersion tests were performed to estimate the corrosion behaviour. Specimen surfaces were observed using light and scanning electron microscopy for microstructure-related assessment of corrosion mechanisms. The corrosion fatigue behaviour was characterized in continuous load increase tests using plastic strain and electrochemical measurements. Continuous load increase tests allow estimating the fatigue limit and determining the failure stress amplitude with one single specimen. Fatigue results showed a significant decrease in the estimated fatigue limit and determined failure stress amplitude with increasing corrosion impact of the environments. This corrosion–structure–property relation was quantitatively described by means of model-based correlation approaches and failure hypotheses. Plastic strain amplitude and deformation-induced changes in electrochemical measurands can be equivalently applied for precise corrosion fatigue assessment. %0 journal article %@ 0026-0843 %A Hort, N., Wiese, B., Dieringa, H., Kainer, K.U. %D 2016 %J Metallurgia Italiana %N 6 %P 105-108 %T Protecting molten Magnesium and its alloys %U 6 %X its own restrictions with maximum working space concentrations. It might be necessary to reuse again fluxes, but they also have limitations. If magnesium and its alloys shall be further used and processed in the EU, alternative ways of magnesium melt protection need to be established within the near future. This contribution will discuss available methods to protect molten Mg and their consequences. %0 journal article %@ 0921-5093 %A Katsarou, L., Mounib, M., Lefebvre, W., Vorozhtsov, S., Pavese, M., Badini, C., Molina-Aldareguia, J.M., Jimenez, C.C., Perez Prado, M.T., Dieringa, H. %D 2016 %J Materials Science and Engineering A %P 84-92 %R doi:10.1016/j.msea.2016.02.042 %T Microstructure, mechanical properties and creep of magnesium alloy Elektron21 reinforced with AlN nanoparticles by ultrasound-assisted stirring %U https://doi.org/10.1016/j.msea.2016.02.042 %X Ceramic AlN nanoparticles were added to a melt of magnesium alloy Elektron21 assisted by mechanical stirring and sonication for deagglomeration. The produced nanocomposite was investigated to determine its metallography, hardness, physical and mechanical properties, and compression creep resistance. Creep tests at a constant temperature of 240 °C and constant stresses of between 70 and 200 MPa revealed an improvement in creep strength after the addition of 1 wt% of AlN nanoparticles. Minimum creep rates were determined and stress exponents were calculated. In order to determine the rate-controlling deformation mechanisms, the concept of a threshold stress for particle strengthened alloys was applied. True stress exponents were calculated for the alloy and for the composite. %0 journal article %@ 0016-9781 %A Wiese, B., Hort, N., Dieringa, H., Kainer, K.U. %D 2015 %J Giesserei-Praxis : Fachzeitschrift fuer alle Bereiche der Giessereitechnik %N 12 %P 601-603 %T Schutz von Magnesiumschmelzen %U 12 %X Im schmelzflüssigen Zustand zeigt Magnesium eine hohe Affinität zu Sauerstoff. Sobald der Sauerstoffgehalt in der Atmosphäre 4 % übersteigt, wird Mg daher entflammen! Damit ergibt sich die Notwendigkeit, Mg-Schmelzen zu schützen. Zurzeit wird standardmäßig SF6 während der Primärproduktion und beim Verarbeiten von Mg-Schmelzen eingesetzt. Bedauerlicherweise ist SF6 jedoch ein Treibhausgas, das ungefähr 23.000 mal wirksamer ist, als CO2. Damit muss SF6 auch bei der Lebensdaueranalyse z.B. von Fahrzeugen berücksichtigt werden. Andere Schutzgase wie zum Beispiel SO2 oder fluorierte Kohlenwasserstoffe wie HFC134a, Novec 612, oder AMCover (= HFC134a) sind bereits als Schutzgase in der Diskussion. Zusätzlich gibt es noch eine Reihe von Schmelzsalzen, die ebenfalls in der Lage sind, Mg-Schmelzen effektiv zu schützen. Allerdings haben Schmelzsalze auch einige Nachteile und fluorierte Gase sind in der EU zusätzlich in der Diskussion. Die aktuellen Regelungen in Europa sehen zudem vor, dass SF6 ab 2018 nicht mehr oder nur sehr beschränkt eingesetzt werden darf. Eine ähnliche Diskussion wird auch für andere fluorierte Gase geführt. Daher ist es notwendig, bekannte Maßnahmen zum Schutz von Mg-Schmelzen neu zu bewerten oder neue Methoden zu entwickeln. %0 journal article %@ 0947-5117 %A Zander, D., Zumdick, N.A., Schnatterer, C., Dieringa, H. %D 2015 %J Materials and Corrosion %N 11 %P 1315-1325 %R doi:10.1002/maco.201408146 %T Aqueous corrosion behavior of creep resistant Mg-Al-Ba-Ca alloys in sodium chloride solutions %U https://doi.org/10.1002/maco.201408146 11 %X The corrosion performance of creep resistant HPDC and PDC (permanent mould direct chill casting) Mg-Al-Ba-Ca alloys was investigated in three aqueous sodium chloride solutions. These ABaX materials were compared to HPDC AZ91D and PDC AZ91D and creep resistant HPDC AE42. Electrochemical measurements and SEM/EDX analysis of original material and corroded cross-sections were conducted, in order to draw a correlation between corrosion behavior and microstructure. The major factor determining the corrosion in ABaX alloys was found to be the shape and distribution of second phases, prompting the formation of microgalvanic corrosion instead of serving as a barrier. %0 journal article %@ 0921-5093 %A Yu, Z., Huang, Y., Dieringa, H., Mendis, C.L., Guan, R., Hort, N., Meng, J. %D 2015 %J Materials Science and Engineering A %P 213-224 %R doi:10.1016/j.msea.2015.08.001 %T High temperature mechanical behavior of an extruded Mg–11Gd–4.5Y–1Nd–1.5Zn–0.5Zr (wt%) alloy %U https://doi.org/10.1016/j.msea.2015.08.001 %X The microstructure–property relation of an extruded Mg–11Gd–4.5Y–1Nd–1.5Zn–0.5Zr (wt%) alloy was investigated by conducting hot compression and high temperature creep at temperatures upto 250 °C. The alloy exhibits an average compressive yield strength (σCYSσCYS) of 363±1 MPa and an average elongation to failure (εCFεCF) of 10.5±0.2% at room temperature, 301±13 MPa and 12.8±1.1% at 200 °C. In creep the minimum creep strain rate (View the MathML sourceε̇min) is 1.94×10−9 s−1 at 175 °C/160 MPa and 6.67×10−9 s−1 at 200 °C/100 MPa. The obtained stress exponent n is in the range of 3.7–4.7, suggesting that the creep is controlled by the dislocation climb mechanism. The improvement in compressive strength and creep resistance is attributed to the fine recrystallized grains, SFs in the grain interior, Mg5RE and LPSO phases at grain boundaries. The alloy exhibits a bimodal texture with 〈0001〉 and 〈View the MathML source101¯0〉 components. Its strengthening effect is determined by the competition between these two texture components. In compressive deformation, the textural evolution from 〈View the MathML source101¯0〉 to 〈0001〉 is mainly attributed to the operation of basal 〈a〉 slip and {View the MathML source101¯2}〈View the MathML source101¯1〉 tensile twinning. This texture evolution is not seen in creep. %0 journal article %@ 0255-5476 %A Dieringa, H., Das, S., Eskin, D., Fan, Z., Katsarou, L., Horstmann, M., Kurz, G., Mendis, C., Hort, N., Kainer, K.U. %D 2015 %J Materials Science Forum, Light Metals Technology 2015 %P 35-40 %R doi:10.4028/www.scientific.net/MSF.828-829.35 %T Twin-roll Casting after Intensive Melt Shearing and Subsequent Rolling of an AM30 Magnesium Alloy with Addition of CaO and SiC %U https://doi.org/10.4028/www.scientific.net/MSF.828-829.35 %X and nanoparticle addition in conjunction with melt treatment by means of external fields. %0 journal article %@ 0255-5476 %A Hort, N., Wiese, B., Dieringa, H., Kainer, K.U. %D 2015 %J Materials Science Forum, Light Metals Technology 2015 %P 78-81 %R doi:10.4028/www.scientific.net/MSF.828-829.78 %T Magnesium Melt Protection %U https://doi.org/10.4028/www.scientific.net/MSF.828-829.78 %X there are similar discussions regarding all other fluorinated hydrocarbons. Due to this, new innovative ways have to be found or old methods have to be renewed to allow Mg industries further safe processing of molten magnesium. This contribution will report the state of the art in protecting molten Mg and alternatives to the use of SF6. %0 journal article %@ 2213-9567 %A Viswanath, A., Dieringa, H., Kumar, K.K.A., Pillai, U.T.S., Pai, B.C. %D 2015 %J Journal of Magnesium and Alloys %N 1 %P 16-22 %R doi:10.1016/j.jma.2015.01.001 %T Investigation on mechanical properties and creep behavior of stir cast AZ91-SiCp composites %U https://doi.org/10.1016/j.jma.2015.01.001 1 %X The room temperature mechanical properties and high temperature creep behavior of AZ91 alloy reinforced with SiCp synthesized via stir casting have been evaluated. The mechanical properties showed improvement with respect to the amount of reinforcement content. The creep testing of the composites carried out at a temperature of 175 °C under constant stress of 80, 100 and 120 MPa reveals different creep characteristics depending upon the reinforcement content and the applied load. The true stress exponents of different composites calculated from minimum creep rate indicate the possible mechanisms of creep deformation. %0 journal article %@ 0921-5093 %A Mondal, A.K., Kesavan, A.R., Reddy, B.R.K., Dieringa, H., Kumar, S. %D 2015 %J Materials Science and Engineering A %P 45-51 %R doi:10.1016/j.msea.2015.02.037 %T Correlation of microstructure and creep behaviour of MRI230D Mg alloy developed by two different casting technologies %U https://doi.org/10.1016/j.msea.2015.02.037 %X The relationship between the as-cast microstructure and creep behaviour of the heat-resistant MRI230D Mg alloy produced by two different casting technologies is investigated. The alloy in both ingot-casting (IC) and high pressure die-casting (HPDC) conditions consists of α-Mg, C36 ((Mg,Al)2Ca), Al–Mn and Sn–Mg–Ca rich phases. However, the HPDC alloy resulted in relatively finer grain size and higher volume fraction of finer, denser network of eutectic C36 phase in the as-cast microstructure as compared to that of the IC alloy. The superior creep resistance exhibited by the HPDC alloy at all the stress levels and temperatures employed in the present investigation was attributed to the more effective dispersion strengthening effect caused by the presence of finer and denser network of the C36 phase. The increased amount of the eutectic C36 phase was the only change observed in the microstructures of both alloys following creep tests. %0 journal article %@ 1013-9826 %A Huang, Y., Dieringa, H., Kainer, K.U., Hort, N. %D 2015 %J Key Engineering Materials, Advances in Fracture and Damage Mechanics XIII %P 365-368 %R doi:10.4028/www.scientific.net/KEM.627.365 %T Deformation-induced dynamic precipitation during creep in magnesium-tin alloys %U https://doi.org/10.4028/www.scientific.net/KEM.627.365 %X The oversaturated solutes in the alloy matrix, which are caused by nonequilibrium phase transformation during casting or T4 treatment, can precipitate in the subsequent annealing treatments or during service at high temperatures. Under deformation the precipitation could be enhanced in comparison to conventional isothermal ageing. The present work investigates the dynamic precipitation of oversaturated Mg-Sn alloys during creep. The influence of this dynamic precipitation on creep properties is discussed. It is found that the distribution of deformation-induced precipitates is inhomogeneous. These precipitates are first formed at grain boundaries and then at deformation bands which are kinetically and thermodynamically favourable. The dynamic precipitation accompanies the volume change of phases, which influences the subsequent formation and growth of voids. Consequently, the creep behaviour also changes due to different precipitation under deformation. %0 journal article %@ 0947-5117 %A Klein, M., Kuhlmann, F., Wittke, P., Dieringa, H., Walther, F. %D 2014 %J Materials and Corrosion %N 10 %P 991-998 %R doi:10.1002/maco.201307327 %T Microstructure-based characterization of the corrosion behavior of the creep resistant Mg–Al–Ba–Ca alloy DieMag422 %U https://doi.org/10.1002/maco.201307327 10 %X The corrosion behavior as well as the microstructure in initial state and after corrosive deterioration were investigated for the newly developed Mg–Al–Ba–Ca alloy DieMag422. In order to investigate the corrosion behavior, potentiodynamic polarization measurements and immersion tests were performed in different NaCl concentrations. The microstructure was observed using light microscopy and combined SEM and EDX studies of the specimens before and after corrosive deterioration. Potentiodynamic polarization measurements and immersion tests showed that DieMag422 has a strong susceptibility to corrosion in NaCl solutions. Light microscope and SEM studies revealed that the difference in the corrosion behavior can be attributed to the different occurrence of the anodic α-Mg phase and the cathodic Ca-rich phase. %0 journal article %@ 2213-9567 %A Huang, Y., Dieringa, H., Kainer, K.U., Hort, N. %D 2014 %J Journal of Magnesium and Alloys %N 2 %P 124-132 %R doi:10.1016/j.jma.2014.03.003 %T Understanding effects of microstructural inhomogeneity on creep response – New approaches to improve the creep resistance in magnesium alloys %U https://doi.org/10.1016/j.jma.2014.03.003 2 %X Previous investigations indicate that the creep resistance of magnesium alloys is proportional to the stability of precipitated intermetallic phases at grain boundaries. These stable intermetallic phases were considered to be effective to suppress the deformation by grain boundary sliding, leading to the improvement of creep properties. Based on this point, adding the alloying elements to form the stable intermetallics with high melting point became a popular way to develop the new creep resistant magnesium alloys. The present investigation, however, shows that the creep properties of binary Mg–Sn alloy are still poor even though the addition of Sn possibly results in the precipitation of thermal stable Mg2Sn at grain boundaries. That means other possible mechanisms function to affect the creep response. It is finally found that the poor creep resistance is attributed to the segregation of Sn at dendritic and grain boundaries. Based on this observation, new approaches to improve the creep resistance are suggested for magnesium alloys because most currently magnesium alloys have the commonality with the Mg–Sn alloys. %0 journal article %@ 1022-6680 %A Song, J., Dieringa, H., Huang, Y., Gan, W., Kainer, K.U., Hort, N. %D 2014 %J Advanced Materials Research, AMI Light Metals Conference 2014 %P 169-176 %R doi:10.4028/www.scientific.net/AMR.1019.169 %T Mechanical Properties and Microstructures of Nano SiC Reinforced ZE10 Composites Prepared with Ultrasonic Vibration %U https://doi.org/10.4028/www.scientific.net/AMR.1019.169 %X In the present investigation, SiC reinforced ZE10 alloy composites were fabricated by direct chill casting assisted with ultrasonic vibration. Two kinds of SiC with a size of 50 nm and 2 μm were chosen. For comparison, ZE10 alloys with and without ultrasound were also fabricated. The microstructures and the distribution of SiC were examined by optical microscopy and scanning electron microscopy. Neutron diffraction was also used to identify the second phases in the composites. In addition, mechanical properties such as hardness, creep and compression were evaluated. The results show that SiC was successfully introduced into the magnesium matrix. After the addition of SiC, the mechanical properties of the composites exhibit a slight decrease, which might be due to the grain coarsening. %0 journal article %@ 1022-6680 %A Dieringa, H., Hort, N., Kainer, K.U. %D 2014 %J Advanced Materials Research, AMI Light Metals Conference 2014 %P 177-183 %R doi:10.4028/www.scientific.net/AMR.1019.177 %T Microstructure and Compression Creep Strength of the Newly Developed Magnesium Alloy DieMag422 %U https://doi.org/10.4028/www.scientific.net/AMR.1019.177 %X alloys and also has proven it is die castable. %0 journal article %@ 1687-8434 %A Mounib, M., Pavese, M., Badini, C., Lefebvre, W., Dieringa, H. %D 2014 %J Advances in Materials Science and Engineering %P 476079 %R doi:10.1155/2014/476079 %T Reactivity and Microstructure of Al2O3-Reinforced Magnesium-Matrix Composites %U https://doi.org/10.1155/2014/476079 %X Performances of metal matrix composites (MMCs) rely strongly on the distribution of particles within the metal matrix but also on the chemical reaction which may occur at the liquid-solid interfaces. This paper presents the chemical reaction between aluminum based particles Al2O3 and Al2O3-AlOOH with magnesium alloys matrixes AZ91 and EL21, respectively, and studies the microstructure of these reinforced composites. Different methods such as transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and XRD were used to highlight these chemical reactions and to identify products. Results demonstrate the formation of MgO particles within the matrix for both composites and also the dissolution of aluminum in the eutectic region in the case of EL21. %0 journal article %@ 1073-5623 %A Sillekens, W.H., Jarvis, D.J., Vorozhtsov, A., Bojarevics, V., Badini, C.F., Pavese, M., Terzi, S., Salvo, L., Katsarou, L., Dieringa, H. %D 2014 %J Metallurgical and Materials Transactions A %N 8 %P 3349-3361 %R doi:10.1007/s11661-014-2321-2 %T The ExoMet Project: EU/ESA Research on High-Performance Light-Metal Alloys and Nanocomposites %U https://doi.org/10.1007/s11661-014-2321-2 8 %X The performance of structural materials is commonly associated with such design parameters as strength and stiffness relative to their density; a recognized means to further enhance the weight-saving potential of low-density materials is thus to improve on their mechanical attributes. The European Community research project ExoMet that started in mid-2012 targets such high-performance aluminum- and magnesium-based materials by exploring novel grain refining and nanoparticle additions in conjunction with melt treatment by means of external fields (electromagnetic, ultrasonic, and mechanical). These external fields are to provide for an effective and efficient dispersion of the additions in the melt and their uniform distribution in the as-cast material. The consortium of 27 companies, universities, and research organizations from eleven countries integrates various scientific and technological disciplines as well as application areas—including automotive, aircraft, and space. This paper gives an overview of the project, including its scope for development and organization. In addition, exemplary results are presented on nanoparticle production and characterization, mixing patterns in metal melts, interface reactions between metal and particles, particle distribution in the as-cast composite materials, and mechanical properties of the as-cast composite materials. The application perspective is considered as well. %0 journal article %@ 0255-5476 %A Srinivasan, A., Huang, Y., Mendis, C., Dieringa, H., Blawert, C., Kainer, K.U., Hort, N. %D 2013 %J Materials Science Forum, Light Metals Technology Conference, LMT 2013 %P 28-32 %R doi:10.4028/www.scientific.net/MSF.765.28 %T Microstructure, Mechanical and Corrosion Properties of Mg-Gd-Zn Alloys %U https://doi.org/10.4028/www.scientific.net/MSF.765.28 %X corrosion resistance. %0 journal article %@ 0255-5476 %A Dieringa, H., Zander, D., Gibson, M.A. %D 2013 %J Materials Science Forum, Light Metals Technology Conference, LMT 2013 %P 69-73 %R doi:10.4028/www.scientific.net/MSF.765.69 %T Creep Behaviour Under Compressive Stresses of Calcium and Barium Containing Mg-Al-based Die Casting Alloys %U https://doi.org/10.4028/www.scientific.net/MSF.765.69 %X mechanical property evaluation. %0 journal article %@ 0921-5093 %A Dieringa, H., Huang, Y., Wittke, P., Klein, M., Walther, F., Dikovits, M., Poletti, C. %D 2013 %J Materials Science and Engineering A %P 430-438 %R doi:10.1016/j.msea.2013.07.041 %T Compression-creep response of magnesium alloy DieMag422 containing barium compared with the commercial creep-resistant alloys AE42 and MRI230D %U https://doi.org/10.1016/j.msea.2013.07.041 %X The development of creep-resistant magnesium alloys that avoid the use of rare-earth alloying elements is an important area of research. The creep response of Mg–Al–Ca alloy containing barium (DieMag422) was compared to that of commercially available creep resistant magnesium alloys AE42 and MRI230D. The creep tests were performed between 175 °C and 240 °C at stresses between 60 MPa and 120 MPa. From the temperature and stress dependence of the minimum creep rate, the apparent activation energy Qc and the stress exponent n for creep were calculated. The concept of a threshold stress was applied. True stress exponents nt close to 5 were calculated. Microstructural investigations and phase analysis were performed on the as-cast materials as well as after creep. Fine precipitates could be identified that justified application of the concept of threshold stress. The DieMag422 alloy shows an improvement in creep resistance at low stresses compared with the other two alloys AE42 and MRI230D. %0 journal article %@ 0921-5093 %A Fechner, D., Blawert, C., Hort, N., Dieringa, H., Kainer, K.U. %D 2013 %J Materials Science and Engineering A %P 222-230 %R doi:10.1016/j.msea.2013.03.053 %T Development of a magnesium secondary alloy system for mixed magnesium post-consumer scrap %U https://doi.org/10.1016/j.msea.2013.03.053 %X Six alloys were prepared by high pressure die casting in order to develop a magnesium secondary alloy system for mixed post-consumer scrap. The alloys were investigated with regard to intermetallic phases, grain structures, mechanical properties and performance in the salt spray test. The results are discussed in relation to the characteristics of the high pressure die casting process. The effect of contamination by copper and compensation for this effect by the addition of zinc were thoroughly investigated for the most promising alloy. It is evident that the alloying elements strontium, silicon and calcium are incorporated in the ternary Zintl phase Sr6.33Mg16.67Si13, while aluminium, zinc, copper and magnesium form the tau-phases Mg32(Alx,Cu1−x)49 and Mg32(Al,Zn)49. The two tau-phases can merge due to isomorphism. Mg32(Al,Zn)49 ensures improved corrosion resistance after the addition of copper. %0 journal article %@ 8756-758X %A Huang, Y., Dieringa, H., Kainer, K.U., Hort, N. %D 2013 %J Fatigue and Fracture of Engineering Materials and Structures %N 4 %P 308-315 %R doi:10.1111/ffe.12000 %T Effects of Sn segregation and precipitates on creep response of Mg-Sn alloys %U https://doi.org/10.1111/ffe.12000 4 %X Mg-Sn alloys are promising for the development of new cheap creep resistant magnesium alloys. In the present paper, the creep behaviours of Mg-Sn and Mg-Sn-Ca alloys were examined at the constant temperature and different stresses. The measurements of stress exponents indicate that the dislocation climbing is the dominant mechanism during the creep of Mg-3Sn or Mg-3Sn-2Ca alloys. The poor creep resistance of the binary Mg-3Sn alloy is caused by the easy movement of dislocation and the segregation of Sn at the boundaries. Both T4 and T6 heat treatments improve the creep resistance of Mg-3Sn alloy due to the alleviation of Sn segregation at grain boundaries and the precipitation of Mg2Sn particles, respectively. Ca is an effective alloying element to increase the creep resistance of Mg-Sn alloys. The Ca addition leads to the formation of thermal stable phases Mg2Ca and CaMgSn in Mg-3Sn-Ca alloys. These two phases effectively hinder the movement of dislocations and the sliding of grain boundaries. On the other hand, the addition of Ca alleviates the segregation of Sn by the interaction of Ca with Mg and Sn to form the phase CaMgSn. %0 journal article %@ 0022-2461 %A Fechner, D., Hort, N., Blawert, C., Dieringa, H., Stoermer, M., Kainer, K.U. %D 2012 %J Journal of Materials Science %N 14 %P 5461-5469 %R doi:10.1007/s10853-012-6436-9 %T The formation of Sr6.33Mg16.67Si13 in magnesium alloy AM50 and its effect on mechanical properties %U https://doi.org/10.1007/s10853-012-6436-9 14 %X of the Al4Sr and the Mg17Sr2 phases. However, after simultaneous alloying with strontium, silicon and calcium the ternary Zintl phase Sr6.33Mg16.67Si13 was detected. This phase forms preferably instead of Al4Sr,Mg17Sr2 andMg2Si. Compared to the two strontium-containing phases, precipitates of the ternary Zintl phase exhibit a rather compact morphology. This results in a higher elongation-at-fracture under tensile stress. %0 journal article %@ 1022-6680 %A Dieringa, H., Kainer, K.U. %D 2012 %J Advanced Materials Research, Processing and Fabrication of Advanced Materials %P 275-278 %R doi:10.4028/www.scientific.net/AMR.410.275 %T Magnesium Matrix Composites: State-of the-art and what’s the future %U https://doi.org/10.4028/www.scientific.net/AMR.410.275 %X A huge number of different process types are in use to produce magnesium-based composites. Depending on the reinforcement type, all the processes can be subdivided into solid state or powder metallurgical (PM) and liquid phase or ingot metallurgical (IM) processes. In this paper we will focus on ingot metallurgy processes. These liquid state processes result quite often in a very good interface of reinforcement with the magnesium matrix. The liquid processes can be further subdivided into infiltration techniques, casting processes and spray deposition. Those are the most inexpensive processing technologies for discontinuous, reinforced magnesium-based composites. When produced using melting processes, nanoparticle-reinforced magnesium composites are expected to improve in strength, due to the grain refinement described in the Hall-Petch relation. When an isotropic distribution of nanoparticles is achieved, the composites are additionally expected to be Orowan-strengthened. That is why nanosized reinforcements are expected to represent the future for improving the properties of magnesium-based metal matrix composites. %0 journal article %@ 0255-5476 %A Dieringa, H., Hort, N., Mueller, S., Kainer, K.U. %D 2011 %J Materials Science Forum, Light Metals Technology V %P 270-273 %R doi:10.4028/www.scientific.net/MSF.690.270 %T Compression creep at 240°C of extruded magnesium alloys containing Gadolinium %U https://doi.org/10.4028/www.scientific.net/MSF.690.270 %X For uses at high temperatures, magnesium alloys containing rare earths have proven to be very suitable. High proportions of melting precipitates contribute to strengthening, even at temperatures above 200°C. If these alloys are extruded, their creep resistance rises even further due to the resulting fine-grained structure. In this paper, magnesium alloys with 10% Gd and additional small amounts of La and Nd are compared with WE43 for compression creep at temperatures of 240°C and stresses between 80 and 150 MPa. The minimum creep rates are determined and the stress exponent evaluated in accordance with the Norton equation. By calculating the threshold stress, the true stress exponents are determined. %0 journal article %@ 0022-2461 %A Dieringa, H. %D 2011 %J Journal of Materials Science %N 2 %P 289-306 %R doi:10.1007/s10853-010-5010-6 %T Properties of magnesium alloys reinforced with nanoparticles and carbon nanotubes: a review %U https://doi.org/10.1007/s10853-010-5010-6 2 %X In some cases an increase in strength in combination with increased ductility was also identified. %0 journal article %@ 1946-3979 %A Anopuo, O., Huang, Y., Hort, N., Dieringa, H., Kainer, K.U. %D 2010 %J The SAE International Journal of Materials and Manufacturing %N 1 %P 202-210 %T Bolt Load Retention and Creep Response of AS41 Alloyed with 0.15 % Ca %U 1 %X Understanding the creep and bolt load retention (BLR) behaviour of promising Mg-Al alloys are crucial to developing elevated temperature resistance alloys. This is especially true for elevated temperature automotive applications with a prevalence of bolted joints. In this study, creep and fastener clamp load response of Mg-Al alloy AS41 was investigated and compared to that of Mg4Al and AS41 micro-alloyed with 0.15 % Ca. A compliance-creep approach was used to model the response of these Mg-Al alloys at bolted joints. The equation prediction of the BLR response and experimental results are in good agreement. AS41+0.15 Ca shows improved creep and BLR properties up to 175 °C. A correlation between the microstructures, creep and BLR results reveal that the formation of a ternary CaMgSi phase is responsible for the improved elevated temperature behaviour. %0 journal article %@ 0255-5476 %A Kainer, K.U., Huang, Y., Dieringa, H., Hort, N. %D 2010 %J Materials Science Forum, THERMEC 2009 %P 73-80 %R doi:10.4028/www.scientific.net/MSF.638-642.73 %T Status of the Development of Creep Resistant Magnesium Materials for Automotive Applications %U https://doi.org/10.4028/www.scientific.net/MSF.638-642.73 %X alloying, microstructural control and the development of new monolithic alloys and composites. %0 journal article %@ 0921-5093 %A Mondal, A.K., Fechner, D., Kumar, S., Dieringa, H., Maier, P., Kainer, K.U. %D 2010 %J Materials Science and Engineering A %N 9 %P 2289-2296 %R doi:10.1016/j.msea.2009.12.010 %T Interrupted creep behaviour of Mg alloys developed for powertrain applications %U https://doi.org/10.1016/j.msea.2009.12.010 9 %X A conventional magnesium alloy, AZ91D, and two creep resistant magnesium alloys, developed for powertrain applications, MRI 153M and MRI 230D, are prepared by high pressure die casting. These alloys are tested for their creep behaviour in the continuous manner, as is the current practice, and in the interrupted manner, which represents the real life situation more closely. It is observed that the interrupted creep tests give rise to a primary creep appearing at the beginning of each cycle resulting in a higher average strain rate than that encountered in the continuous creep tests. Further, the shorter the cycle time, higher is the average strain rate in the interrupted creep tests. A higher average strain rate will give rise to a higher strain over the same period. This is attributed to the recovery taking place during the cooling and heating between two cycles. The effect of additional precipitation during interrupted creep tests depends on the nature of the precipitates. The additional precipitation of β phase during the cooling and heating between two cycles increases the steady state strain rate in the AZ91D and MRI 153M alloys, whereas the additional precipitation of C36 phase during the cooling and heating between two cycles decreases the steady state strain rate in the MRI 230D alloy. %0 journal article %@ 0177-9516 %A Dieringa, H., Hort, N., Kainer, K.U. %D 2009 %J Praxis der Naturwissenschaften - Chemie in der Schule %N 3 %P 9-13 %T Neue Entwicklungen bei der Anwendung von Magnesiumlegierungen %U 3 %X No abstract %0 journal article %@ 0921-5093 %A Dieringa, H., Hort, N., Kainer, K.U. %D 2009 %J Materials Science and Engineering A %P 382-386 %R doi:10.1016/j.msea.2008.06.051 %T Investigation of minimum creep rates and stress exponents calculated from tensile and compressive creep data of magnesium alloy AE42 %U https://doi.org/10.1016/j.msea.2008.06.051 %X Creep specimens prepared of magnesium alloy AE42 were investigated under constant load in compressive and tensile creep respectively. Material was cast via the squeeze casting process in order to obtain a dense microstructure without pores. Creep tests were performed at constant temperatures between 150°C and 240°C and constant applied stresses between 40 MPa and 120 MPa until minimum creep rate ε&s was reached. It could be seen that the minimum creep rates of compressive creep tests were smaller compared to tensile creep tests, and the difference increased with increasing applied stress. Stress exponents, n, were determined according to the Norton-equation and it was found that a threshold stress σ had to be introduced into the analysis. The threshold stress is based on strengthening by Al-RE (aluminum-rare earths) precipitates. Calculating the true stress exponent, n, deformation mechanisms during creep could be clarified. %0 journal article %@ 1946-3979 %A Anopuo, O., Huang, Y., Dieringa, H., Hort, N., Kainer, K.U., Abdul, K.K. %D 2009 %J The SAE International Journal of Materials and Manufacturing %N 1 %P 103-110 %T Mechanical Properties and Corrosion Performance of AZ-Mg Alloy Modified with Ca and Sr %U 1 %X Any new Mg-alloys for the power train application in the automotive industry should have better elevated temperature mechanical and corrosion properties than the traditional AZ91 magnesium alloy. The price of AZ-Mg alloy modified with Ca and Sr, which can have adequate properties suitable for its service conditions, is expected to be comparable to that of AZ91 alloy and cheaper than AE42 alloy. The formation of thermally stable intermetallics, which are necessary for the improvement of creep properties, makes it a promising candidate for high temperature applications. This work investigates the mechanical and corrosion properties of AZ-Mg alloy modified with (Ca, Sr) in comparison with those of AZ91; the work included bolt load retention (BLR) and ageing behaviour. The aim is to give a preliminary evaluation of the overall performance of this modified AZ alloy. It is found that this alloy has a superior BLR property compared to AZ91 alloy with a good corrosion resistance. %0 journal article %@ 0016-979X %A Dieringa, H., Kainer, K.-U. %D 2009 %J Giesserei Rundschau %N 7-8 %P 114-119 %T Technologische Eigenschaften und Potential von Magnesiumlegierungen %U 7-8 %X Dieser Artikel gibt einen kurzen Überblick über die Verwendung von Magnesiumlegierungen mit Gussverfahren in der Vergangenheit und in der Gegenwart. Dabei werden die gebräuchlichen Legierungen vorgestellt und neuere Entwicklungen aufgezeigt, welche insbesondere in den Bereich der Warmfestigkeit und Kriechbeständigkeit zielen. %0 journal article %@ 0921-5093 %A Poletti, C., Dieringa, H., Warchomicka, F. %D 2009 %J Materials Science and Engineering A %N 1-2 %P 138-147 %R doi:10.1016/j.msea.2009.03.007 %T Local deformation and processing maps of as-cast AZ31 alloy %U https://doi.org/10.1016/j.msea.2009.03.007 1-2 %X An apparent activation energy of 147 kJ/mol at the peak flow stress was calculated by a sinh-type constitutive equation suggesting dynamic recrystallisation and twinning formation. %0 journal article %@ 0005-5670 %A Dieringa, H., Kainer, K.U. %D 2009 %J Banyaszati es Kohaszati Lapok - Kohaszat %N 6 %P 9-15 %T Magnesiumoetvoetek technologiai tulajdonsagai es lehetoesegei %U 6 %X Dieser Artikel gibt einen kurzen Überblick über die Verwendung von Magnesiumlegierungen mit Gussverfahren in der Vergangenheit und in der Gegenwart. Dabei werden die gebräuchlichen Legierungen vorgestellt und neuere Entwicklungen aufgezeigt, welche insbesondere in den Bereich der Warmfestigkeit und Kriechbeständigkeit zielen. %0 journal article %@ 1359-6462 %A Huang, Y., Dieringa, H., Hort, N., Abu Leil, T., Kainer, K.U., Liu, Y. %D 2008 %J Scripta Materialia %N 10 %P 894-897 %R doi:10.1016/j.scriptamat.2008.01.011 %T Effects of segregation of primary alloying elements on the creep response in magnesium alloys %U https://doi.org/10.1016/j.scriptamat.2008.01.011 10 %X of magnesium alloys in the future. %0 journal article %@ 0925-8388 %A Huang, Y., Dieringa, H., Hort, N., Maier, P., Kainer, K.U., Liu, Y. %D 2008 %J Journal of Alloys and Compounds %N 1-2 %P 238-245 %R doi:10.1016/j.jallcom.2007.09.071 %T Evolution of microstructure and hardness of AE42 alloy after heat treatments %U https://doi.org/10.1016/j.jallcom.2007.09.071 1-2 %X The AE42 magnesium alloy was developed for high pressure die casting (HPDC) from low-aluminum magnesium alloys. In this alloy the rare earth (RE) elements were shown to increase creep resistance by forming AlxREy intermetallics along the grain boundaries. The present work investigates the microstructure of squeeze cast AE42 magnesium alloy and evaluates its hardness before and after heat treatments. The change in hardness is discussed based on the microstructural observations. Some suggestions are given concerning future design of alloy compositions in order to improve high temperature creep properties even further. It is shown that the microstructure of the squeeze-cast AE42 alloy is stable at high temperature 450 °C. The subsequent solution and ageing treatments have a limited effect on the hardness. The weak age-hardening is attributed to the precipitation of small amount of Mg17Al12-phase with the use of about 0.7 wt.% aluminum. The heat treatment to achieve a maximum increase in the hardness is: solution treatment at 450 °C for 5–10 h followed by an ageing treatment at 190–220 °C for about 5 h. %0 journal article %@ 1662-9779 %A Frank, H., Hort, N., Dieringa, H., Kainer, K.U. %D 2008 %J Solid State Phenomena, Semi-Solid Processing of Alloys and Composites X %P 43-18 %R doi:10.4028/www.scientific.net/SSP.141-143.43 %T Influence of Processing Route on the Properties of Magnesium Alloys %U https://doi.org/10.4028/www.scientific.net/SSP.141-143.43 %X on different microstructures that are obtained by the different processing routes. While in the case of AZ91D, TM is showing advantages compared to HPDC for room temperature applications, the NRC in combination with the heat resistant alloy leads to an improvement of creep rates by two orders of magnitudes. %0 journal article %@ 0255-5476 %A Abu Leil, T., Huang, Y., Dieringa, H., Hort, N., Kainer, K.U., Bursik, J., Jiraskova, Y., Rao, K.P. %D 2007 %J Materials Science Forum, Progress in Light Metals, Aerospace Materials and Superconductors %P 69-72 %R doi:10.4028/www.scientific.net/MSF.546-549.69 %T Effect of Heat Treatment on the Microstructure and Creep Behavior of Mg-Sn-Ca Alloys %U https://doi.org/10.4028/www.scientific.net/MSF.546-549.69 %X The development of new Mg-Sn based alloys that have shown improved corrosion resistance needs further investigations to develop standard alloys for industrial use. In the present study, the influence of heat treatment was investigated by examining the creep resistance of Mg-Sn and Mg-Sn-Ca alloys at 85 MPa under 135 °C identify the best conditions to improve the mechanical properties of such alloys. Additionally, the changes in microstructure of these alloys were studied and analysed by light microscopy, X-ray diffraction and scanning electron microscopy. It was found that the heat treatments can affect the microstructure of the binary alloy while no apparent change in the microstructure was found in the Mg-Sn-Ca alloys, indicating that the second phase CaMgSn is thermal stable in this alloy. Based on the obtained results, the relationship between the microstructure and creep behaviour are discussed. %0 journal article %@ 0933-5137 %A Dieringa, H., Kainer, K.U. %D 2007 %J Materialwissenschaft und Werkstofftechnik %N 2 %P 91-96 %R doi:10.1002/mawe.200600114 %T Magnesium - der Zukunftswerkstoff fuer die Automobilindustrie? %U https://doi.org/10.1002/mawe.200600114 2 %X zu schaffen. %0 journal article %@ 0921-5093 %A Arunachaleswaran, A., Pereira, I., Dieringa, H., Huang, Y., Hort, N., Dhindaw, B.K., Kainer, K.U. %D 2007 %J Materials Science and Engineering A %P 268-276 %R doi:10.1016/j.msea.2007.01.043 %T Creep behavior of AE42 based hybrid composites %U https://doi.org/10.1016/j.msea.2007.01.043 %X heat treatment. %0 journal article %@ 0921-5093 %A Kumar, S., Dieringa, H., Kainer, K.U. %D 2007 %J Materials Science and Engineering A %P 367-370 %R doi:10.1016/j.msea.2006.11.041 %T Thermal cycling behaviour of the magnesium alloy based hybrid composite in transverse direction %U https://doi.org/10.1016/j.msea.2006.11.041 %X The thermal cycling behaviour of a creep-resistant AE42 alloy reinforced with 20 vol% saffil short fibre as well as various volume fractions of saffil short fibre and SiC particulate has been examined in the transverse direction in the temperature range of 30–350 ◦C. For comparison, the thermal cycling behaviour of the unreinforced AE42 alloy is also examined. It is found that the linear instantaneous CTE curves of composites show a positive deviation from linearity above 215–230 ◦C, which is attributed to the release of residual compressive strain arising from the squeeze casting process. The experimentally obtained CTE of the composites is compared with the theoretically calculated values. The CTE of the hybrid composite is calculated by a linear subtraction of the expected decrease in CTE with the addition of SiC particulates from the CTE calculated for composite containing short fibres alone assuming a rule of mixture. However, it is observed that the fibres and particulates interact in a more complex manner and the decrease in CTE with the addition of particulates in a hybrid composite is greater than that obtained by the simple linear subtraction assuming a rule of mixture. %0 journal article %@ 0019-493X %A Arunachaleswaran, A., Dhindhaw, B.K., Dieringa, H., Hort, N., Kainer, K.U. %D 2007 %J Transactions of the Indian Institute of Metals %N 2-3 %P 87-91 %T Microstructure Characterisation and creep properties of AE42 based hybrid composites prepared by squeeze casting process %U 2-3 %X compared to SiCp. Heat treatment of the composites improved the distribution of the precipitates in the composites. Hardness characteristics of the composites have been studied. %0 journal article %@ 0142-1123 %A Huang, Y., Hort, N., Dieringa, H., Maier, P., Kainer, K.U. %D 2006 %J International Journal of Fatigue %N 10 %P 1399-1405 %R doi:10.1016/j.ijfatigue.2006.02.038 %T Investigations on thermal fatigue of aluminium-and magnesium-alloy based composites %U https://doi.org/10.1016/j.ijfatigue.2006.02.038 10 %X and subsequent heat treatment, on the thermal strain were discussed. It is shown that the thermal strain was affected by experimental condition of the thermal cycling and the strength of matrix. After thermal cycling, the hardness decreases due to the occurrence of the matrix overageing and recovery. %0 journal article %@ 0019-493X %A Hort, N., Dieringa, H., Kainer, K.U. %D 2005 %J Transactions of the Indian Institute of Metals %N 4 %P 703-708 %T Hot tearing of magnesium alloys %U 4 %X alloy development is of major importance to achieve an improvement of the property profile. Unfortunately the use of alloying elements like rare earth elements, calcium, silicon, strontium etc. is also decreasing the castability and alloys containing these elements have not yet been introduced to continuous casting as well. Therefore the new alloys have to be selected carefully in accordance to their castability regarding different casting processes. In this work AZ based alloys modified with Ca and Zn will be investigated regarding their hot tearing behavior. %0 journal article %@ 0266-3538 %A Huang, Y., Hort, N., Dieringa, H., Kainer, K.U. %D 2005 %J Composites Science and Technology %N 1 %P 137-147 %R doi:10.1016/j.compscitech.2004.07.002 %T Analysis of instantaneous thermal expansion coefficient curve during thermal cycling in short fiber reinforced AlSi12CuMgNi composites %U https://doi.org/10.1016/j.compscitech.2004.07.002 1 %X Short fiber reinforced AlSi12CuMgNi composites have potential applications as engine components in automobile industry. In these engine components, the dimensional stability is of great concern. Thermal cycling experiments can approximately simulate the real working conditions of the materials and give an evaluation of the dimensional changes during their service in the changing temperature environments. Due to the fact that in metal matrix composites the thermal strain is dependent on the phase transformation, the matrix plastic yielding and the physical damage of reinforcement, analysis of thermal strain curves could allow not only insight into their thermal expansion behavior but also into the phase transformation and possible matrix plastic deformation behavior caused by large internal thermal stresses. Compared with the thermal strain curve, the instantaneous CTE curve can clearly supply more information because it is the differential of thermal strain over temperature. It is useful to differentiate whether the appearance of a knee on the thermal strain curve is caused by the phase transformation and/or by the matrix plastic deformation, especially in metal matrix composites with age hardenable matrix. In the present paper, the aging behaviors in both the unreinforced and ceramic reinforced AlSi12CuMgNi piston alloys are investigated and discussed by analyzing the instantaneous CTE curve, DTA curve and hardness tests. The matrix plastic deformation caused by thermal stresses is discussed based on the observation of CTE divergence in the longitudinal and transverse directions. The effects of both the SiO2 content and subsequent heat treatment on the critical temperature, above which the CTE divergence occurs, are discussed. Finally, the effects of precipitation and matrix plastic deformation on the residual strain after thermal cycling are also preliminary evaluated. %0 journal article %@ 0019-493X %A Thakur, S., Dieringa, H., Dhindaw, B.K., Hort, N., Kainer, K.U. %D 2005 %J Transactions of the Indian Institute of Metals %N 4 %P 653-659 %T Thermal cycling and creep studies of AM50+Nd magnesium alloy based carbon fiber, SiC particulate and in-situ Mg2Si reinforced habrid composites %U 4 %X Magnesium based hybrid composites with carbon fiber, SiCp and in-situ Mg2Si reinforcements have been prepared through squeeze infiltration technique. The results of the studies done on measurement of the coefficient of thermal expansion (CTE) after thermal cycling have been presented. In the present paper, an attempt has been made to characterize the micro-structural evolution and the plastic deformation behaviour of these hybrid composites in the as cast condition and after thermal cycling. Attempt has also been made to study the effect of thermal treatment on the thermal expansion behaviour of the AM50+Nd magnesium based hybrid composites in terms of CTE values. Composites containing Nd show lower values of CTE compared to the base alloy. Further creep compression tests were carried out on these composites. Composites consisting of rare earth element Nd show much better creep properties as compared to the base alloy matrix. Results of creep compression tests carried out for some other Mg and Al base alloys and composites have also been included for comparison. %0 journal article %@ 1359-835X %A Kumar, S., Dieringa, H., Kainer, K.U. %D 2005 %J Composites / A %N 3 %P 321-325 %R doi:10.1016/j.compositesa.2004.07.005 %T Effect of particulate content on the thermal cycling behaviour of the magnesium alloy based hybrid composites %U https://doi.org/10.1016/j.compositesa.2004.07.005 3 %X volume fractions of saffil short fibre and SiC particulate has been examined in the temperature range of 30–350 8C. It is found that the plastic deformation due to internal thermal mismatch stresses above 250 8C increases and coefficient of thermal expansion decreases with increasing volume fraction of SiC particulates. The only microstructural change observed after thermal cycling is an increased precipitation in the matrix. %0 journal article %@ 0921-5093 %A Dieringa, H., Huang, Y., Maier, P., Hort, N., Kainer, K.U. %D 2005 %J Materials Science and Engineering A %P 85-88 %R doi:10.1016/j.msea.2005.08.005 %T Tensile and compressive creep behaviour of Al2O3 (Saffil) short fiber reinforced magnesium alloy AE42 %U https://doi.org/10.1016/j.msea.2005.08.005 %X The development of metal matrix composites (MMCs) is one possibility to overcome the disadvantage of poor high temperature creep properties of present magnesium alloys. Short fiber reinforcement improves the high temperature creep resistance of magnesium alloys. Tensile and compressive creep properties of magnesium alloy AE42 (4 wt.% aluminium and 2 wt.% rare earths) reinforced with 20 vol.% alumina (Saffil®) fibers were investigated in the temperature range of 175–300 °C and stress range of 40–140 MPa, respectively. The MMC was manufactured by direct squeeze casting. The materials investigated show different behaviour depending on type of loading. Stress exponents were calculated from the stress dependence of the minimum creep rate in order to find indications for the possible mechanisms of deformation. The need of correcting the stress dependence of the minimum creep rate by a threshold stress was found. Electron microscopy was performed to investigate the fracture surface of a tensile creep specimen. %0 journal article %@ 0255-5476 %A Bowles, A., Dieringa, H., Blawert, C., Hort, N., Kainer, K.U. %D 2005 %J Materials Science Forum, Magnesium – Science, Technology and Applications %P 135-138 %R doi:10.4028/www.scientific.net/MSF.488-489.135 %T Investigations in the Magnesium-Tin system %U https://doi.org/10.4028/www.scientific.net/MSF.488-489.135 %X Currently most magnesium alloys are based on the Mg-Al system and this system is reasonably well developed. Nevertheless, the alloy system has some disadvantages - while having excellent castability and adequate room temperature mechanical properties Mg-Al alloys show poor creep resistance. This has led to investigations in other magnesium based systems; magnesium forms alloys with a large number of elements and, indeed a number of magnesium systems show good creep resistance. In this work, the Mg-Sn system has been chosen for study. %0 journal article %@ 0255-5476 %A Dieringa, H., Bowles, A., Hort, N., Kainer, K.U. %D 2005 %J Materials Science Forum, Materials Structure & Micromechanics of Fracture %P 271-274 %R doi:10.4028/www.scientific.net/MSF.482.271 %T Microstructural Development in Tension and Compression Creep of Magnesium Alloy AE42 %U https://doi.org/10.4028/www.scientific.net/MSF.482.271 %X formation of Mg17Al12. %0 journal article %@ 1359-6454 %A Huang, Y., Hort, N., Dieringa, H., Kainer, K.U., Liu, Y. %D 2005 %J Acta Materialia %N 14 %P 3913-3923 %R doi:10.1016/j.actamat.2005.04.039 %T Microstructural investigations of interfaces in short fiber reinforced AlSi12CuMgNi composites %U https://doi.org/10.1016/j.actamat.2005.04.039 14 %X Short fiber reinforced AlSi12CuMgNi composites find applications as engine components in the automobile industry. The addition of short fibers raises the interfacial reaction between the fiber and the matrix and modifies the matrix microstructure. Reaction products could change the matrix composition and alter the matrix in a physical metallurgical manner, such as the microstructure and ageing behavior. The present work investigated the microstructure in the interfacial regions and in the matrix, as well as the ageing behavior in Saffil®- and Kaowool®-fiber reinforced composites using scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray analysis, differential thermal analysis and microhardness tests. The effects of reinforcements on the distribution of the alloying elements and on the interfacial reactions were investigated and discussed. The interfacial reaction mechanisms were analyzed based on thermodynamics and kinetics. Finally, the relationship between the interfacial reaction and ageing behavior was discussed. It was shown that the distribution of the alloying elements is affected by the addition of fibers. The degree of interfacial reaction depends on the reinforcement composition. The growth of the reaction products is controlled by the cation diffusion along the new interface between reaction product and fiber. The ageing hardening is weakened due to the depletion of the alloying element magnesium; caused by the interfacial reaction. %0 journal article %@ 0266-3538 %A Kumar, S., Mondal, A., Dieringa, H., Kainer, K.U. %D 2004 %J Composites Science and Technology %N 9 %P 1179-1189 %T Analysing hysteresis and residual strains in thermal cycling curves of short fibre reinforced Mg-MMCs %U 9 %X %0 journal article %@ 1440-0731 %A Dieringa, H., Hort, N., Kainer, K.U. %D 2004 %J Advances in Technology of Materials and Materials Processing %N 2 %P 136-141 %T Magnesium based MMCs reinforced with C-fibers %U 2 %X %0 journal article %@ 1438-1656 %A Huang, Y., Hort, N., Dieringa, H., Kainer, K.U. %D 2004 %J Advanced Engineering Materials %N 11 %P 883-888 %R doi:10.1002/adem.200400057 %T Micro-Strain Induced by Thermal Cycling in the Short Fiber Reinforced AlSi12CuMgNi Piston Alloys and AE42 Magnesium Alloys %U https://doi.org/10.1002/adem.200400057 11 %X %0 journal article %@ 0255-5476 %A Kumar, S., Ingole, S., Dieringa, H., Kainer, K.U. %D 2003 %J Materials Science Forum %P 2119-2124 %T Thermal Cycling of Mg-MMC's %U %X %0 journal article %@ 0266-3538 %A Kumar, S., Ingole, S., Dieringa, H., Kainer, K.U. %D 2003 %J Composites Science and Technology %P 1805-1814 %T Analysis of thermal cycling curves of short fibre reinforced Mg-MMCs %U %X %0 journal article %@ 1641-8611 %A Dieringa, H., Hort, N., Kainer, K.U. %D 2003 %J Kompozyty / Composites %N 7 %P 275-278 %T Compression creep of short fibre reinforced magnesium alloy AE42 %U 7 %X