High-performance 3D-printed alloys for cars and airplanes

A lightweight material that can be 3D printed and is stable enough to carry heavy loads: this is highly interesting for the automotive and aircraft industries because it could save up to 50% CO₂ in the mobility sector. The aluminium alloy Scalmalloy® appears to have precisely such properties. In order to understand the reason for the high load-bearing capacity and to further optimise alloys in the future, researchers have carried out measurements in collaboration with Mercedes Benz, Premium AEROTEC, and Airbus.

Dr Xingxing Zhang while working on the STRESS-SPEC instrument. © FRM II / TUM

Dr Xingxing Zhang while working on the STRESS-SPEC instrument. © FRM II / TUM

Stable alloys despite strong applied forces
So far, studies on the Scalmalloy® alloy have mainly focused on the influence of its composition and crystal structure on the alloy’s stability. However, this information is insufficient for applications in which the alloy must retain its shape under high forces or return to its original shape after an elastic deformation. When an alloy is stretched, microscopic changes occur initially. This behaviour is the so-called microplasticity of the material, where atoms within the material change their position slightly, thus showing a dislocation. Macroscopic deformation, visible to the naked eye, occurs only later. This is known as the macroplasticity of the alloy. “We need a deep understanding of the material properties for a safe and efficient use of the aluminium alloy,” says Dr Xingxing Zhang, who conducted his research in cooperation with representatives from the automotive and aviation industries.

X-rays to examine the samples
Dr. Xingxing Zhang is currently working in Beijing at the Institute of High Energy Physics of the Chinese Academy of Sciences. He performed the measurements at the DESY research facility in Hamburg together with Dr. Weimin Gan, instrument scientist at the Helmholtz Zentrum Hereon at the MLZ. At DESY, X-rays are available to resolve crystal structures and their defects with a high resolution. The scientists compared the 3D printed samples, once untreated and once after direct aging of the sample, and in both cases before and during the application of a tensile load. Although direct aging is an established method, its influence on the alloy’s microplasticity has yet to be fully clarified. They used the special machine developed for the STRESS-SPEC instrument to apply the tensile load.

To investigate how the material changes during stretching, the researchers subjected the aluminium sample Scalmalloy® from the manufacturer Premium AEROTEC GmbH to tensile stress and measured it with X-rays. © International Journal of Plasticity

To investigate how the material changes during stretching, the researchers subjected the aluminium sample Scalmalloy® from the manufacturer Premium AEROTEC GmbH to tensile stress and measured it with X-rays. © International Journal of Plasticity

Defect concentration is key to improving the alloy
The scientists identified distinct deformation stages in the material’s behaviour through continuous tensile loading. They measured both macroscopic and microscopic deformations, as well as their defect concentrations, to gain insights into the underlying mechanisms. Interestingly, the scientists found that the deformation stages exhibited by as-built and direct-aged aluminium alloys differ significantly, with distinct defect concentrations. Dr. Xingxing Zhang developed a novel three-dimensional defect-concentration-based crystal plasticity model to model this complex behaviour, which accurately predicts macroscopic and microscopic properties, including defect concentrations. The defect concentrations play a crucial role in determining the stability of the alloys, and now, scientists understand their evolution better when applying a tensile force. “This is an important step forward”, says Dr. Xinxing Zang.
Using X-ray scattering on the sample, the researchers could calculate the material’s stress. Simulations supported the experimental results. Neutrons, such as those available at the MLZ, on the other hand, could provide information on the positions of the atomic nuclei and supplement the measurements.