Fatigue performance measurement of a secondary cast Al-Si-Cu-Mg alloy recycled from cylinder head with minor element additions

Abstract

This study systematically investigated the combined effects of minor additions of Sr, Fe, and Mn, together with T6 heat treatment, on intermetallic phase evolution and fatigue performance of a secondary Al-Si-Cu-Mag cast alloy. The alloy was obtained by melting end-of-life motor vehicle engine cylinder heads. Novelty of this work is based on the proposed recycling approach and the establishment of a direct correlation between intermetallic morphology modification and fatigue life in recycled cylinder head alloys. The base alloy exhibited coarse, needle-like eutectic silicon particles and Fe-rich intermetallic compounds such as Al₂Cu and AlCuNi. Addition of 0.02 wt.% Sr transformed silicon morphology into refined fibrous structure, while Fe and Mn additions modified the formation of Fe-rich phases into less harmful α-intermetallic phases. After T6 heat treatment, silicon particles became rounded and fragmented, and Al₂Cu phases fully dissolved. Among as-cast alloys, Sr-modified variant demonstrated highest fatigue life (610,399 cycles), confirming the beneficial role of microstructural refinement in delaying crack initiation. The findings demonstrated that controlled alloy modification combined with heat treatment enabled recycled Al–Si–Cu–Mg alloys achieve enhanced fatigue resistance. These results provide practical guidelines for producing reliable automotive powertrain components and contribute to sustainable materials engineering.