Effects of Heat Treatment on Microstructure and Mechanical Properties of As-extruded Mg-Zn-Y-Zr Alloy

The effects of different heat treatment parameters on the microstructure and mechanical property of as-extruded Mg-4.8Zn-1.2Y-0.4Zr magnesium alloy were described based on the experimental results and analyses. The results indicate that the microstructure of the alloy changes obviously during heat treatment process. After T4 solution treatment, although the alloy grains grow obviously, the plasticity of the alloy is enhanced greatly. This is mainly due to the massive fish-bone W-phase decomposed into fine granular W phase, which reduces the pinning effect of the grain boundary. After T5 heat treatment, besides W-phase, there is a small amount of Mg-Zn phase precipitated in the alloy, which can improve the performance of the alloy. After T6 heat treatment, the W-phase has been almost completely decomposed into Mg-Zn and Mg-Y phase. The dispersively distributed phases greatly improve the strength and plasticity, which increases the ultimate tensile strength and elongation from 311 MPa and 16.89% in as-extruded alloy to 374 MPa and 21.97%, respectively. At last the most suitable scheme for heat treatment of Mg-4.8Zn-1.2Y-0.4Zr magnesium alloy is (500 °C/2 h+200 °C/48 h).