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 alpha-Mg, beta-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 alpha-Mg, beta-Li matrix and grain boundary, lots of round granular AlLi phase distributed in the beta-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 alpha-Mg phase. In addition, the volume fraction of alpha-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 alpha-Mg phase and precipitation strengthening. The fracture morphology of the two as-cast alloys is composed of tiny dimples and cleavage planes.