- The role of composition control on the structure property relationships in Mg-Nd-Zn alloys
- Forel Research Project "THIXOM"
- PhD project "Microstructure-property relationships of Mg-Ca-Y alloys"
- PhD project "Development of Mg-Gd alloys with Ag or Ca to be used as degradable implant materials"
- PhD project "Influences of rare earth elements contents on its strengthening in Mg"
- PhD project "Influence of processing on solidification and properties of nanoparticle reinforced magnesium alloys"
- PhD project "Influences of intermetallics on the biodegradability of Mg-Gd/Nd alloys"
Magnesium alloys with nanosized reinforcement
Compared to aluminium alloys magnesium alloys still suffer from lower mechanical strength and creep resistance especially at elevated temperatures. In order to reach the goal of substituting aluminium alloys with magnesium alloys will only be achieved when comparable mechanical properties. A reinforcement of fibres and/or particles in the micrometer scale has already been in the focus of research for some decades but has never come into industrial application. In recent years low cost nano-particles are available which promise to reinforce magnesium alloys in a way that they promote Orowan-strengthening much better than micrometer particles. It is expected that strength and creep resistance in a temperature range up to 250°C will be significantly improved. Development of processes for introduction of nano-particles into the magnesium alloy melt and resulting high strength and creep resistant materials would strongly support the leading position of magnesium based activities at Hereon.
One of the challenges will be the processing route via melt stirring. It is important that nano-particles are distributed randomly in the matrix and no agglomeration of particles occurs. From experience with micro-particle reinforced magnesium alloys it can be expected that additional support during stirring has to be conducted. Power ultrasound can help avoid agglomeration as well as support fine disperse distribution of particles. This is affected by micro-sized bubbles which form during intense sonification and then implode instantaneously. The second important challenge is the finding of ideal combinations of ceramic particles and magnesium melt. Depending on alloying elements and ceramic composition chemical reactions may occur. A thin layer promotes a good bonding between both materials but when contact is extended reinforcement might simply desolve. Knowledge of chemical fundamentals as well as process development has to be built up.
Additionally, microstructure analysis via SEM/TEM investigation, X-ray diffraction, mechanical properties, and creep response at room and elevated temperatures has to be evaluated. Thermal expansion and wear behaviour will be investigated in a second stage.
DFG-project "The role of composition control on the structure property relationships in Mg-Nd-Zn alloys"
Mg alloys are ideal for weight critical applications, where the reduction in weight correlates with a reduction in energy consumption. However, the property profiles of commercially viable magnesium alloys are not sufficient for many of the applications envisaged. The design of Mg alloys through control of both the alloy composition and distribution of secondary phases through the microstructure is important in realizing the full potential of these alloys. It has been reported that the addition of Zn to Mg-RE alloys (RE=rare earth) results in modification of the microstructures and the resulting mechanical properties at relatively low RE content. However, at present only RE additions with high solubility in Mg, such as Gd and Y, have been investigated systematically to understand the role of RE:Zn ratio on the microstructure and resultant mechanical properties in a range of processing conditions. Nd is a lower cost and low solubility RE addition that has shown to enhance the strength of Mg alloys through formation of fine scale particles that hinder plastic deformation effectively in Mg-Nd and Mg-Nd-RE alloys. It is expected that the presence of Zn will enhance the mechanical properties through the modification of microstructure at a relatively low Nd content.
The ultimate goal of this investigation is to develop a lower cost Mg alloy system for structural applications with tunable mechanical properties through modification of the alloy composition and controlled heat treatments. The ability to design the microstructure and resultant mechanical properties through formation of solid-state precipitation along with intermetallic particles at the grain boundaries would allow the development of alloys with a synergistic combination of enhanced strength and ductility but with low cost for the increased use of magnesium alloys in commercial applications.
Within the scope of the proposed project a range of alloys with varying Nd: Zn ratios will be investigated to understand the microstructural evolution during solidification using in situ X-ray diffraction experiments and subsequent ex situ electron microscopy investigations. The information on the type of intermetallic phase present, their formation temperature and the volume fraction of these phases will be used to verify and improve the Mg rich side of the Mg-Nd-Zn phase diagram that is currently available. The role of heat treatments on modifying the intermetallic phases formed during solidification and formation of new solid-state precipitates during such heat treatments is to be investigated with the aid of electron microscopy. This would provide for a further step during which the microstructure and the resultant mechanical properties could be modified. The mechanical properties of the cast and the heat treated alloys will be evaluated both at room and at elevated temperature to understand the role of alloy composition, intermetallic phases and the thermal history on such properties.
Forel research Project "THIXOM"
Magnesiumwerkstoffe besitzen erhebliches Leichtbaupotenzial, das sie unter anderem für die Verwendung in der funktionsintegrativen Fahrzeugbaugruppe Karosserie, und hier speziell für Tragstrukturen, prädestiniert. Dieses Potenzial zur Gewichtsreduktion ist durch die Verwendung partikel- oder faserverstärkter Magnesiumlegierungen sowie deren Kombination mit Kunststoffen in hybriden Strukturen noch erweiterbar. Die Forschungs- und Entwicklungsarbeiten im Verbundvorhaben im Projekt FOREL-THIXOM zielen insbesondere auf die dazu notwendigen Systeme zur Herstellung der entsprechenden Magnesiumlegierungen sowie die Bereitstellung eines großserientauglichen Thixomoulding-Urformverfahrens mit modularen und temperierten Formwerkzeugen. Im Vorhaben wird eine prototypische Fertigungsanlage zur Verarbeitung modifizierter Magnesiumwerkstoffe erstellt. Die Validierung der konstruktiven und prozesstechnischen Innovationen erfolgt anhand einer generischen Karosseriestruktur für die Aufnahme von Anbauteilen. THIXOM at Forel platform
PhD poject "Microstructure-property relationships of Mg-Ca-Y alloys"
Magnesium alloys have great potential applications as structural materials, but with the exception of some casting products, few wrought magnesium alloys are being used due to their poor plastic formability. It is well known that the limited number of slip systems of hexagonal crystal structure leads to the poor plastic formability of Magnesium alloys. Recently, it is reported that the addition of Calcium and Yttrium can weaken the texture of Magnesium alloys, which contributes to the improvement of ductility. However, the effect of Y and Ca on deformation mechanism combined with the texture evolutions of the Mg-Ca-Y system has not been investigated systematically. In this study, the relationship between mechanical properties and microstructure of Mg-Ca-Y system will be investigated in detail.
The aim of this research is to investigate the Ca and Y effect on the microstructure and mechanical properties of the newly developed Mg-Ca-Y system at both room and high temperatures, and further to understand the deformation mechanism combining the quantitatively lattice strain and texture evolutions. The obtained results are expected to supply fundamental insights for alloy composition optimization, which have potential applications as heat resistant materials and in the field of degradable biomaterials.
Several alloys with various Ca:Y ratios will be investigated to evaluate the Mg rich end of the Mg-Ca-Y phase diagram based on the intermetallic phases determined by XRD and TEM analysis of the as-cast alloys. The mechanical properties of as-cast and as-extruded alloys will be measured at both room and elevated temperatures to investigate the role of composition and microstructure on such properties. The tensile deformation behaviour of the extruded samples will be investigated through in-situ lattice strain measurement with the combination of ex-situ texture analysis at the different selected plastic strains.
PhD project "Development of Mg-Gd alloys with Ag or Ca to be used as degradable implant materials"
Mg alloys are a promising candidate for biodegradable implant applications. This study aims at the systematic development of Mg-Gd based alloys (total alloying element lower than 5 wt. %) which show a good combination of mechanical and degradation properties. All the alloys were prepared by permanent mold casting. The mechanical properties, corrosion resistance, cytocompatibility and antibacterial properties will be optimized by different additions of alloying elements (Ag, Ca) and solution heat treatment (T4).
PhD project "Influences of rare earth elements contents on its strengthening in Mg"
With the increasing demands of lightweight metal magnesium alloy in the industry areas of automobile, aviation, medical machinery, etc. a great deal of research has focused on the enhancement of the mechanical properties of magnesium alloy through adding proper alloying elements and optimize processing techniques. However, the present applications of magnesium alloys are still limited. The main obstacles are their low strength and formability at room temperature and poor creep resistance at high temperatures. In order to enlarge the applications of magnesium alloys, a number of REs content alloys have been developed. The drastic improvement of mechanical properties and creep resistance are obtained in the past decades.
In order to investigate the strengthening mechanisms caused by REs, the alloying element Gd and Nd were selected. The alloys with different solid solubility were prepared by additions of different contents of Gd. All the as-cast Mg-Gd specimens were performed with homogenization treatment in order to alleviate the segregation of Gd before investigating the effect of Gd content on the solid solution strengthening. Mg-Gd T4 alloys and as-cast Mg-Nd alloys were prepared by extrusion at 450 °C with a ratio of 62.7:1.The mechanical properties of hardness, tensile or compressive yield stress were selected and measured.
The effects of Gd and Nd contents on the Young’s modulus of binary Mg-Gd and Mg-Nd alloys, and the association between the microstructure and elastic modulus of these Mg alloys have been study. The solid solution strengthening on the hardness and yield strength for polycrystalline Mg-Gd alloys with Gd contents between 2 and 15 wt.% were investigate. Additionally, the Effect of Nd content on tension-compression yield asymmetry and intermetallic phase on mechanical behavior of Mg-Nd alloys were also studied.
PhD project "Influence of processing on solidification and properties of nanoparticle reinforced magnesium alloys"
The aim of the project is to produce homogeneously dispersed nanoparticle reinforced magnesium alloys with melt shearing process and to optimize the amount and the size of added nanoparticles in terms of microstructure, mechanical properties and the high temperature properties. The size, wettability and thermal expansion of the nanoscaled particles are selected to gain the optimal mechanical properties. Processing parameters need to be found for optimum combination of properties. In order to investigate the effect of processing on solidification and properties of metal matrix nanocomposites (MMNCs), the microstructure and composition needs to be analysed. Properties, like density, coefficient of thermal expansion, microhardness, tensile and compressive strength and creep response of the composites at elevated temperatures will be determined. The improvement of the mechanical properties of the nanoparticle reinforced magnesium alloy will be discussed based on the Orowan-Strengthening and Hall-Petch effect.
PhD project "Influences of intermetallics on the biodegradability of Mg-Gd/Nd alloys"
The main obstacle for clinical applications of biodegradable magnesium alloys is to select a suitable degradation rate for implantation in different physiological environments. The present investigation will focus on the influences of intermetallics on the degradability of magnesium alloys. Mg-Gd and Mg-Nd alloys were prepared. For Mg-Nd alloys, since there is almost no solubility for Nd in Mg matrix, Mg-Nd alloys with different contents of Nd can provide different specified amounts of intermetallics and allow an insight on their impacts on biocorrosion behaviour. Regarding Mg-Gd alloys, Gd has a large solid solubility in Mg and is selected to investigate the influence of solute atoms and intermetallics on degradability. In order to accurately control the amount of intermetallics for degradation, the aging kinetics of Mg-Gd alloys will be quantitatively evaluated. Applied methods are thermodynamic calculations, XRD and 3-D X-ray nanotomography. The morphology, size, distribution and amount of intermetallics on the degradation behavior of Mg-Gd alloys will be investigated by weight loss method, cell adhesion and live/dead staining. A qualitative or even quantitative relationship between amount of precipitates and degradable properties will be established.
- EU Project "ExoMet"
- Viscosity of molten magnesium
- PhD poject "Grain refinement of Al-free Mg alloys by SiC inoculation"
EU Project "ExoMet"
To meet the future EU challenges of light-weighting and pollution reduction, especially relevant in transportation, it is necessary to improve the cast ability of light alloys, to enhance grain and eutectic refinement in monolithic alloys, and to develop new high-strength nano-composites using nano-reinforcers which have only recently become available. Significant mechanical property improvements are foreseen in ExoMet - including 50% increases in tensile strength and ductility, as well as creep resistance up to 300-350°C (currently limited to about 200°C in Al and Mg alloys). This applies to both shape castings and wrought products like extruded profiles, bar, cable, sheet and plate.
DFG-project in cooperation with Prof. Dr.-Ing. Rainer Schmid-Fetzer, Institut für Metallurgie, TU Clausthal "Elaboration of a model for the viscosity of liquid alloys with predictive capability by implementation of consistent thermodynamic descriptions and validation by experimental investigation of liquid magnesium alloys"
The viscosity of unary, binary and multi-component liquid alloys is of great importance in the theory of liquid metal behaviour and also for fluid flow behaviour in metallurgical processes, such as casting, welding, and solidification. The goal of this project is to develop a model for the viscosity of liquid alloys and to combine it with dedicated experimentation on liquid magnesium alloys. The predictive capability of that model to calculate the concentration and temperature dependence of viscosity over a wide range of multicomponent alloys shall be enhanced by the implementation of fully consistent Calphad-type thermodynamics of these alloys. The model will be validated against a wide range of metallic liquids, such as solder, aluminium and magnesium alloys and shall be useful for implementation in integrated software for calculation of thermodynamic and thermophysical properties but also for solidification modelling at large.
Combination of experimental data and analytic modelling
Moreover, new and systematic experimental data for both the viscosity and density of liquid magnesium alloys will be generated and combined with the analytical model incorporating thermodynamic data. This will enable a reliable calculation of liquid viscosity even for rapidly changing values of (residual) liquid composition and temperature, relevant for solidification processing and modelling of magnesium alloys.
EU Project "Tailored biodegradable magnesium implant materials" (MagnIM)
MagnIM is a Marie Curie Initial Training Network of eight partners from six different European countries. Our aim is the development of tailored biodegradable magnesium implant materials. By training twelve PhD students we will meet these challenges by the development of new aluminium (Al)-free Mg implant materials with properties specific for a bone-related application especially in children.
BMWi Joint Research Project Magnesium components with repairable polymeric coatings for the reduction of weight and reduced maintenance efforts and simultaneous improvement of passenger comfort and safety
Magnesium alloys offer a weight reduction of around 30 % compared to Al alloys. But they still suffer from low corrosion resistance in aircraft applications. To improve the performance of Mg alloys they will be combined with mechanical-chemical resistant surface coatings based on duromeric polymers which can be repaired. During manufacturing of these composite materials by forging the heat of the forging die will be used to coat Mg components in the final processing step.
BMWi Joint Research Project MagHyM – "Development and characterization of Mg-Al hybrid materials for corrosion and fire resistant cabin components for civil airplanes"
The aim of this project is the development of corrosion and fire resistant Mg-Al hybrid structural components for the civil aviation. By further development of the direct strip cast process a manufacturing route shall be developed that allows the production of new Mg-Al hybrid materials. It is assumed that these new materials alloy the reduction of weight of components up to 20-25 %.
Cooperation with LMpv
The Division Processing implements MagHyM in cooperation with LMpv Leichtmetall Produktion & Verarbeitung, a production site for new, ultralight metallic materials, situated in Rheinland-Pfalz. The BMWi-Project terminates on 31. December 2014.
PhD project "Grain refinement of Al-free Mg alloys by SiC inoculation"
A fine-grain microstructure is important to improve the service performance for both cast and wrought Mg alloys. For aluminium-free Mg alloys, Zr addition is an extremely effective grain refining treatment, but is expensive. Reducing the consumption of Zr and the cost are therefore the major challenges. Our recent study showed that SiC addition is a feasible and cost effective alternative for the grain refinement of Mg-Zn and Mg-Mn alloys. Hence, the aim of present work is to investigate the grain refinement effect in Mg-xZn and Mg-xMn alloys with different amount of SiC additions and their mechanisms. The results show that the average grain size of Mg-3Zn alloy is reduced by 45% with 0.3% SiC addition. The grain size keeps stable with further increasing the content of SiC due to the amount of activated particles as the nucleation substrates is saturated. Microstructural observations show that Mn-(Fe)-Si-(C) intermetallic phase locates inside Mg-Zn or Mg-Mn grains . They may serve as the nuclei during solidification, leading to the grain refinement. The interaction between SiC and the minor element Mn or impurity element Fe is suggested to explain the grain refinement.
 Jian Gu, Yuanding Huang, Karl Ulrich Kainer, Norbert Hort: Role of SiC in grain refinement of aluminum -free Mg-Zn alloys; Magnesium Technology 2016, TMS (The Minerals, Metals & Materials Society), Edited by: Alok Singh, Kiran Solanki, Michele V. Manuel, and Neale R. Neelameggham (2016) 177-181.