Effect of Y content on microstructure evolution and tensile properties of Mg-8Li-3Al-2Sn-xY alloys

The design of new ultra-light Mg-Li alloys have great significance in aerospace and other fields. In this paper, Sn and Y elements were simultaneously added into Mg-8Li-3Al (wt%) alloy and the effect of Y content on microstructure evolution and tensile properties of Mg-8Li-3Al-2Sn-xY (wt%) alloys was studied. The as-cast Mg-8Li-3Al-2Sn alloy is composed of α-Mg + β-Li duplex-phase matrix, fine MgLiAl2 phase and coarse fishbone-like Li2MgSn phase. As Y element is added, granular Al2Y phase is formed, and grain size of α-Mg phase decreases significantly with shape changing from well-developed coarse dendritic to equiaxed dendritic. After hot extrusion, α-Mg phase is elongated along the extrusion direction, and β-Li phase undergoes complete dynamic recrystallization and transforms into fine equiaxed grains. The addition of 0.5% Y improves the tensile properties of as-cast Mg-8Li-3Al-2Sn-0.5Y alloy. However, the tensile properties show a downward trend with further increase of Y content. Hot extrusion significantly enhances the tensile properties of Mg-8Li-3Al-2Sn-xY alloys. Similarly, strength reaches the highest when the Y content is 0.5% for extruded Mg-8Li-3Al-2Sn-xY alloys.