Aluminium alloys are versatile materials and are used in numerous applications due to their light weight and high yield strength. Nevertheless, a huge amount of aluminium alloy products reach their end-of-life every year, such as automotive or aircraft parts, kitchen and packaging products, etc. [1, 2]. The amount of energy needed for the production of fresh aluminium products is much bigger than that needed for its recycling. Thus, if a bigger fraction of these end-of-life alloys gets reused, the energy consumption would be considerably reduced. Here we present experimental results verifying a computer-based rapid alloy development approach that predicts novel alloys purely based on mixing of automobile and aircraft aluminium waste fractions without refinement. Besides thermophysical properties determination and phase selection during solidification the aim was to verify material properties required for certain production processes, like e. g. additive manufacturing.

We present results for three different aluminium alloys with varying silicon content and solute element fractions produced by melting and casting a mixture of aluminium scraps. Intermetallic phases formed in the Al-Si alloys due to other solute elements were microstructurally characterised using scanning electron microscopy (SEM). In DSC experiments melting temperatures and the respective melting interval and specific heat capacity have been measured. Thermal diffusivity in the alloys was determined employing light flash analysis. The synthesised alloys were also cut into thin slices, subjected to laser-treatment in order to create melt pool tracks, which is one common method to test rapid solidification effects as a preliminary assessment of the suitability for additive manufacturing. SEM analysis of the predicted Al-alloys showed no susceptibility to hot cracking. Fig. 1 shows one micrograph of a sample cut perpendicular to the laser track with a finer microstructure visible in the rapidly solidified melt pool and no cracks. The results obtained from the various characterisation measurements of the different mixtures were compared in order to determine the best composition for future casting and additive manufacturing applications of the predicted alloys.

References

[1] D. Raabe et al., "Making sustainable aluminum by recycling scrap: The science of “dirty” alloys," Progress in Materials Science, 2022, p. 100947.

[2] B. Zhou, B. Liu, S. Zhang, R. Lin, Y. Jiang and X. Lan, "Microstructure evolution of recycled 7075 aluminum alloy and its mechanical and corrosion properties," Journal of Alloys and Compounds, 2021, p. 160407.