Characterization of innovative secondary aluminium alloys for HPDC structural automotive components

The automotive sector is pushing toward sustainability and circularity has intensified the interest in increasing the use of recycled materials. Aluminium, with its high recyclability and favorable strength-to-weight ratio, is a strategic material in this transition. However, integrating high-recycled-content aluminium alloys into structural vehicle components presents critical challenges, particularly due to the accumulation of residual elements such as iron (Fe), copper (Cu), and zinc (Zn), which compromise mechanical properties and processability. This doctoral research, conducted within the framework of the European SALEMA project, addresses these challenges by developing and validating secondary AlSi10MnMg alloys, primarily derived from end-of-life (EoL) scrap, for application in high-pressure die casting (HPDC) of automotive Body-in-White (BiW) structural components. The scope of the study encompassed alloy analysis through thermodynamic simulations, laboratory-scale casting trials, microstructural and mechanical characterization, and the industrial-scale casting of a full demonstrator component. CALPHAD-based simulations using Thermo-Calc software were applied to evaluate solidification behavior under both equilibrium and Scheil-Gulliver conditions. Laboratory-scale trials with six alloy variants were performed to evaluate castability, with Zn identified as the most detrimental impurity. The first full characterization was performed on the variants at laboratory-scale cast samples. Following the down-selection of the optimal variant, a large structural component was cast at industrial scale. The comparative analysis of laboratory and industrial castings revealed that while industrial parts had greater porosity due to complex geometry, they exhibited fewer casting defects and finer SDAS, leading to superior microstructural and mechanical uniformity. The mechanical results confirmed the reliability of hardness and bending tests in capturing the influence of casting quality and alloying elements. Bending tests proved to be effective in isolating the ductile behavior of the surface-refined matrix, where the influence of internal defects is reduced due to the skin effect. The hardness measurements correlated well with observed microstructural features and supported the presence of localized surface strengthening in the component. Corrosion resistance tests confirmed the compatibility of the alloy with automotive coating technologies, even in the presence of Cu levels exceeding EN 1706 limits. Overall, the study demonstrates the technical feasibility of using high-recycled-content AlSi10MnMg alloys in HPDC structural automotive applications, providing a scalable and sustainable path forward. The integration of thermodynamic modeling, experimental validation, and industrial casting highlights a robust methodology for qualifying secondary alloys in demanding engineering contexts. The conclusions of this work and the SALEMA project show that increasing EN 1706 limits for Fe, Cu, and Zn could enable greater use of recycled EoL scrap in structural aluminium alloys, supporting circular economy goals without compromising mechanical or corrosion performance in automotive applications.