Effect of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3A1-(1,2,3)Sn alloys

The effects of Sn content on microstructure and tensile properties of as-cast and as-extruded Mg-8Li-3Al-(1,2,3)Sn (wt.%) alloys were investigated by X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and tensile test. It is found that, as-cast Mg-8Li-3Al-(1,2,3)Sn alloys consist of alpha-Mg+beta-Li duplex matrix, MgLiAl2 and Li2MgSn phases. Increasing Sn content leads to grain refinement of alpha-Mg dendrites and increase in content of Li2MgSn phase. During hot extrusion, complete dynamic recrystallization (DRX) takes place in beta-Li phase while incomplete DRX takes place in alpha-Mg phase. As Sn content is increased, the volume fraction of DRXed alpha-Mg grains is increased and the average grain size of DRXed alpha-Mg grains is decreased. Increasing Sn content is beneficial to strength but harmful to ductility for as-cast Mg-8Li-3Al-(1,2,3)Sn alloys. Tensile properties of Mg-8Li-3Al-(1,2,3)Sn alloys are improved significantly via hot extrusion and Mg-8Li-3Al-2Sn alloy exhibits the best tensile properties.