The role of high recycled content and heat treatments on microstructure, mechanical properties, and sustainability for an AlSi10MnMg structural automotive component

Abstract

Secondary aluminum alloys are produced with end-of-life scraps and are gaining importance for environmental sustainability, thanks to their low intrinsic carbon footprint and energy saving compared to the primary ones. They are increasingly used in the automotive sector for large and complex cast components. However, recycled alloys contaminants like Fe promote the formation of brittle intermetallic compounds, which negatively affect tensile strength and ductility. This study compares the mechanical performance and environmental impact of primary and recycled high pressure die casting AlSi10MnMg (EN AB 43500) alloy under as-produced and heat-treated conditions. Samples were extracted from a die-cast automotive component and subjected to annealing and an optimized T6 heat treatment to balance strength and ductility. Microstructural analysis using field emission scanning electron microscopy revealed a similar pores area fraction, as well as shape, size, and distribution of brittle acicular β-Al₅FeSi and polygonal α-Al₁₅(Fe,Mn)₃Si₂ Fe-rich phases in the primary and recycled alloys under different heat treatment conditions. This similarity justifies the comparable mechanical behavior of the primary and recycled alloy, characterized by limited ductility in the as-produced condition, often insufficient for safety-critical structural components. Heat treatments significantly improved ductility, increasing it by 40–50 % after annealing and nearly doubling it after T6 due to the fragmentation, spheroidization, and coarsening of the eutectic Si. However, the microstructure change reduces strength by a third after annealing and by 20 % after T6, ultimately influencing the final fracture mechanisms. Moreover, heat treatments increase energy consumption, with annealing and T6 leading to about 25 % and 30 % rises, respectively, making them justified only for elongation enhancement.