Metals for the future

Components for cars and airplanes should be even lighter and more robust in the future - to save fuel and reduce CO₂ emissions. This requires optimized materials that have to be produced using new manufacturing processes. The relatively new friction extrusion process is particularly promising. Prof Benjamin Klusemann's department is taking a closer look at this process within his ERC Grant “MA.D.AM” in order to make it work for everyday use. In collaboration with colleagues from Hereon and the Pacific Northwest National Laboratory in the USA, experiments are being carried out at DESY.

His team is looking at promising new aluminum alloys, especially those made from a mixture of a lot of aluminum and smaller amounts of copper and lithium as well as other chemical elements. But the mixture alone is not enough. How a material is produced and processed is crucial for its application, especially in terms of deformation and temperature. "Everything together ultimately influences the structure inside the material and its properties," says Klusemann. Specifically, he is interested in a new metal processing method that he uses to shape the aluminum alloy. In this process, the material is not only subjected to high pressure but also to friction in order to process it; in this case into wires that could be used in 3D metal printers in the future, for example. "We are the first in the world to have developed and set up an in situ experiment for the friction extrusion process at a synchrotron source," he says. The development and planning of these experiments was based on the so-called "FlexiStir", a multifunctional friction welding system that was developed together with colleagues from GEMS at Hereon. This cross-institute and cross-departmental development of complex experiments at the synchrotron is one of Hereon's strengths. The departments of Prof Benjamin Klusemann and Dr Peter Staron have been working together for many years.

The development of this test stand is an elementary component of his current ERC grant “MA.D.AM”. An ERC grant is the most prestigious European research grant awarded by the European Research Council and is equivalent to a science prize.

Aluminum alloys have been used in various forms in industry for many years. These include profiles in cars and airplanes, for example in the form of rails into which seats are inserted or those that support the engine or structure in the car body. To shape the alloy into an elongated profile, the material is heated until it is so soft that it can be pressed through a die. This process is known as "extrusion". With the friction extrusion process, which Klusemann is investigating at DESY, it is hoped to achieve even better properties than with more classic approaches. The aim is also to be able to process other materials in the near future.

For his experiments, he clamps small blocks of material into a device, which then presses a punch into the material with a hole in the middle. The novelty: this punch rotates at the same time to generate friction. This heats the material and slowly softens it, allowing it to be formed into wires. The pressure and rotation ultimately result in the material having a different nano- and microstructure than before. With the help of X-ray diffraction, the research group can observe exactly how the structure forms in the material - and even how the aluminum, copper and lithium atoms in the material come together to form small particles. "These nanometer-sized particles make the material particularly resistant despite its low weight," says Klusemann.

With further tests on the Hereon beamlines at DESY, his team now wants to find out how manufacturing of aluminium components can be further optimized for future production. "To do this, we need to understand even more precisely what happens at the micro and nano level when the material is subjected to both pressure and friction." He is working closely with colleagues from the Pacific Northwest National Laboratory (PNNL), a research laboratory in the USA, where the friction extrusion process has also been studied in recent years. "Our aim is to use X-rays to analyze the material during processing. This is only possible with examinations directly in the material, with so-called in situ measurements, which are only possible in close cooperation with partners with different areas of expertise," says Klusemann. He finds it astonishing that the concept of friction extrusion was conceived back in 1991 but was only implemented for the first time a few years ago in a special machine that is now available at Hereon and PNNL.