Microstructure and mechanical properties of as-extruded and as-aged Mg–Zn–Al–Sn alloys

Abstract

The microstructure and mechanical properties of as-extruded and as-aged Mg–4Zn–1.5Al (in wt%) alloy rods were investigated systematically. The results indicate that the addition of Sn to as-extruded Mg–4Zn–1.5Al alloys can lead to the formation of Mg2Sn and refine the grain size as the Sn content is less than 2%. However, higher Sn results in the coarsening of grain and secondary precipitates. Among the as-extruded alloys, Mg–4Zn–1.5Al–2Sn alloy exhibits optimal combination of strength and ductility, the ultimate tensile strength (UTS), yield strength (YS) and elongation (εf) are 305MPa, 195MPa and 15%, respectively. A subsequent T5 heat treatment was carried out on as-extruded Mg–4Zn–1.5Al–2Sn. After aging at 150°C for 5–50h, there are much more secondary precipitates, which results in improved strength and ductility. The best combination of strength and ductility is as-extruded ZAT422 alloy aging at 150°C for 40h, the UTS, YS and ɛf are 314MPa, 236MPa and 18%, respectively.