Effect of Heat Treatment on the Fatigue Characterization of an Automotive Component Produced by HPDC Using a Recycled AlSi10MnMg Alloy

Al–Si–Mg alloys are increasingly employed in HPDC automotive structural components due to their lightweight potential and recyclability. In this context, the use of recycled AlSi10MnMg alloys represents a promising strategy to reduce the environmental footprint of aluminum components. However, the fatigue performance of these alloys, particularly when subjected to different heat treatments, remains insufficiently understood. This study investigates the fatigue behavior and fracture mechanisms of a 75 pct recycled AlSi10MnMg alloy, using specimens directly extracted from an industrial HPDC automotive component. Specimens retaining the original as-cast surface were subjected to three different heat treatment conditions: E-coating simulation (EC), artificial aging (AA), and annealing (AN). Microstructural characterization, nanoindentation mapping, and high-cycle fatigue tests were combined with fractographic analysis to correlate microstructural features with fatigue crack nucleation and propagation mechanisms. Results revealed a heterogeneous cross-sectional microstructure, with a discontinuous eutectic-rich skin layer over a coarser dendritic core, generating a hardness gradient that significantly influenced fatigue behavior. Among the investigated conditions, AA provided the highest fatigue strength (138 ± 4 MPa), while EC and AN showed lower performance. Fractographic observations revealed that fatigue crack nucleation was associated with the local discontinuity of the skin layer, whereas crack propagation and overall fatigue resistance were primarily governed by the hardness distribution induced by heat treatment. Finally, the environmental impact assessment focused on the effect of the AA and EC heat treatments further indicated that AA, despite its additional processing energy, reduces the overall life-cycle environmental burden by extending component lifetime.