Tailoring microstructures and mechanical properties of cast Mg-Zn-Al-Mn alloys through alloying with Cu, Sn, and Y

Mechanical properties of cast Mg alloys remain insufficient for demanding applications. In this study, individual and combined effects of Cu, Sn, and Y additions on secondary phase characteristics and α-Mg grain refinement in a cast Mg-8Zn-1Al-0.5Mn (ZAM810) alloy were systematically investigated. The results demonstrate that Cu alloying can transform coarse MgZn with a network-like morphology into fine MgZnCu and Al-rich MgZnCu. Besides, the constitutional supercooling caused by Cu solutes effectively refines α-Mg grains and promotes a more uniform distribution of secondary phases. However, excessive Cu content (> 0.5wt.%) leads to the transition of Cu-containing phases from isolated block-like forms to interconnected lath-like morphologies, degrading mechanical properties. Based on the optimized 0.5wt.% Cu addition, Sn alloying enhances solid solution strengthening, further refines α-Mg grains and modifies the size and distribution of MgZn, MgZnCu, and Al-rich MgZnCu phases. More importantly, Y alloying on the basis of 0.5wt.% Cu addition effectively transforms coarse lath/needle-like secondary phases into fine granular-like, significantly reducing the size and improving the distribution. This results in an excellent balance between strength and ductility of the cast ZAM810 alloy. These findings provide valuable insight into microstructure design for achieving strength-ductility synergy in cost-effective cast Mg-Zn based alloys.