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

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 305 MPa, 195 MPa 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 5-50 h, 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 40 h, the UTS, YS and ɛf are 314 MPa, 236 MPa and 18%, respectively.