Effects of Li content on microstructure and mechanical properties of as-cast Mg−xLi−3Al−2Zn−0.5Y alloys

Abstract

The effects of Li content on the microstructure and mechanical properties of the as-cast Mg−xLi−3Al−2Zn− 0.5Y (LAZx32-0.5Y) alloys were investigated by XRD, SEM, TEM, hardness tester and universal testing machine. The results show that the matrix of the alloy transforms from α-Mg to α-Mg+β-Li and then to β-Li when the Li content increases from 4% to 14% (mass fraction). All LAZx32-0.5Y alloys contain AlLi and Al2Y, while MgLi2Al appears only in the alloy containing the β-Li matrix. As the Li content increases, the content of AlLi and MgLi2Al gradually increases, while the content of Al2Y does not change much. As the Li content increases from 4% to 10%, the ultimate tensile strength and hardness of the as-cast LAZx32-0.5Y alloys gradually decrease while the elongation gradually increases. The corresponding fracture mechanism changes from cleavage fracture to quasi-cleavage fracture and then to microporous aggregation fracture. This is mainly attributed to the decrease of α-Mg and the increase of β-Li in the alloy. When the Li content continues to increase to 10% and 14%, the yield strength, ultimate tensile strength and hardness of the as-cast LAZx32-0.5Y alloys gradually increase, while the elongation decreases sharply, which is mainly attributed to the nano-scale MgLi2Al uniformly distributed in the β-Li matrix.