Microstructure and mechanical properties of heat-treated Mg–6.2Li–3.5Al–3Y alloy

Abstract

To further improve the mechanical properties of Mg–Li alloys, the microstructure evolution and mechanical properties of Mg–6.2Li–3.5Al–3Y alloy after different heat treatment processes (holding at 250 °C, 300 °C, 350 °C and 400 °C for 30 min, 60 min and 120 min, respectively) have been investigated in this study. It is found that the Mg2Y eutectic disappears after heat treatment, and the volume fraction of Al2Y precipitated phase decreases first and then increases with increasing heat treatment time. In addition, The tensile test results reveal that the tensile strength of the alloy increases first and then decreases with the increase of heat treatment time. The tensile strength and ductility of the alloy reach 182 MPa and 12.7%, respectively, after heat treatment at 400 °C for 30 min, which are 35.8% and 36.5% higher than those of as-cast alloy. The evolution of Mg2Y eutectic and Al2Y phase during heat treatment processes at different time and temperatures are analyzed in detail. It can be concluded that the tensile strength of the alloy is improved by the combined effects of precipitation hardening due to the formation of Al2Y phase, and the solid solution strengthening due to the decomposition of Mg2Y eutectic and Al2Y precipitated phase.