Effects of Ag Addition on the Microstructure and Elevated Temperature Mechanical Properties of as-cast Mg-6Gd-2Y-Nd-xAg-0.4Zn-0.5Zr Alloys

In order to broaden applications of magnesium rare earth alloys in aerospace fields, the microstructure and mechanical properties of as-cast Mg-6Gd-2Y-Nd-0.4Zn-0.5Zr alloys can be improved by Ag alloying, and the elevated temperature strengthening mechanism is revealed. The microstructure analysis shows that the as-cast alloys mainly consist of α-Mg equiaxed grain and network-like β-Mg5(Gd,Y,Nd,Ag,Zn) phase. The addition of the Ag exhibits a strong grain refinement effect and promotes the formation of the second phase in the as-cast alloys. It is noteworthy that the content of Ag exceeds 1.5 wt%, and a small amount of Mg17Ag2(Gd,Y,Nd,Zn) phase is formed at grain boundaries. The results of tensile test reveal that the as-cast Mg-6Gd-2Y-Nd-1.5Ag-0.4Zn-0.4Zr alloy has excellent mechanical properties. Compared with the Mg-6Gd-2Y-Nd-0.4Zn-0.4Zr alloy, the ultimate tensile strength is 220 MPa at 25 °C and 225 MPa at 250 °C, which are improved by 15.7 and 11.3%, respectively.