Effect of Y content on microstructure and mechanical properties of as-cast Mg-8Li-3Al-2Zn alloy with duplex structure

In this study, effect of Y on microstructure and mechanical properties of as-cast Mg-8Li-3Al-2Zn alloy was investigated. The results show that microstructure of the Mg-8Li-3Al-2Zn alloy mainly consists of α-Mg, β-Li, AlLi and MgLiAl2 phases. With addition of Y, the Al2Y compound forms and increases gradually, the AlLi phase decreases and the β-Li phase increases, meanwhile, the microstructure is significantly refined and equiaxed. The addition of 1 wt% Y produces the smallest grain size. Mg-8Li-3Al-2Zn-0.5Y alloy exhibits an optimum combination of tensile properties with the ultimate tensile strength, yield strength and elongation of 153.0 MPa, 218.5 MPa and 16.9%, which are improved by about 6.4%, 13.2% and 13.4% compared with those of Mg-8Li-3Al-2Zn alloy (143.8 MPa, 193.0 MPa and 14.9%), respectively. The mechanisms of improvement are related to grain refinement and second phase strengthening.