Microstructure evolution and mechanical properties of as-cast Al–Mg–Si alloy induced by Fe addition

This study systematically investigates the role of Fe content in governing the microstructure and mechanical properties of recycled Al–Mg–Si alloys. Through multiscale characterization (SEM, TEM, DSC, and tensile testing), we reveal that Fe-rich intermetallic compounds (IMCs) transition from needle-like β-AlFeSi phases at low Fe levels to interconnected Chinese script α-AlFeSi networks at higher Fe contents. The addition of iron refined the grain size, which decreased from 149.1 μm when the iron content was 0.15 wt% to 118.9 μm when the iron content was 1.05 wt%. Meanwhile, the ultimate tensile strength was enhanced, whereas the plasticity exhibited a non-monotonic trend. The 1.05Fe alloy achieves an exceptional elongation of 15.7 % (67 % higher than 0.40Fe) due to α-AlFeSi-induced crack deflection and strain delocalization, despite elevated porosity. DSC analysis confirms Fe reduces the formation temperature of primary α-Al and suppresses Mg2Si formation via solute competition. This work establishes that optimizing Fe content transforms detrimental β-phase-dominated structures into beneficial α-phase architectures, enabling strength-ductility synergy in recycled Al alloys.