Effect of Al on Microstructure and Mechanical Properties of Mg-10Li-3Zn-1Y Alloys

Mg-Li alloys with the nominal composition Mg-10Li-xAl-3Zn-1Y (x = 0 and 3) alloys were prepared by vacuum induction melting. Mg-10Li-3Zn-1Y alloy is mainly composed of α-Mg, β-Li, and Mg₂₄Y₅ phases. Adding Al results in the formation of AlLi, MgLi₂Al, and Al₂Y phases, but the Mg₂₄Y₅ phase disappeared. The precipitated phase Mg₂₄Y₅ presents irregular strips and particles uniformly distributed on the α-Mg, β-Li matrix and grain boundary, lots of round granular AlLi phase distributed in the β-Li matrix, elongated phase at the grain boundary and the petal-like phase inside the crystal are the MgLi₂Al phase, and bright white regular Al₂Y phase scattered at the grain boundary and within the α-Mg phase. In addition, the volume fraction of α-Mg phase increases with the addition of Al element. The ultimate tensile strength of the alloy increases from 173.53 to 190.56 MPa after adding Al element, but the elongation decreases from 18.89 to 16.52%. The mechanisms of improvement are related to the increase in the volume fraction of the α-Mg phase and precipitation strengthening. The fracture morphology of the two as-cast alloys is composed of tiny dimples and cleavage planes.