Effect of heat treatment on mechanical properties and microstructure evolution of Mg-9.5Gd-4Y-2.2Zn-0.5Zr alloy

Abstract

Regarding the as-cast Mg-9.5Gd-4Y-2.2Zn-0.5Zr alloy, the effect of heat treatment on its properties at room temperature (RT), as well as the mechanical properties and microstructure evolution of various peak-aging samples at different tensile temperatures were discussed in this article. The results indicated that the optimal heat treatment process of the alloy was: 520 °C × 24 h + 200 °C × 112 h. Under this condition, the yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) at RT were: 238 MPa, 327 MPa and 2.5 %, respectively. As the tensile temperature increases, the strength increases firstly and then decreases, but the ductility increases monotonously. The microstructures evolution of 200 °C peak-aging (200PA) and 250 °C peak-aging (250PA) samples were different with the increasing tensile tenperature. When tensile test processed at 150°C, the dense β' phase and rod-shaped basal γ' phase will be formed in the 200PA sample. However, at 300 °C, the β' phases disappeared. The β' and LPSO phases in the 250PA sample coarsened gradually as the tensile temperature increased, and 14H-LPSO phases were formed during tensile at 300 °C. The 200PA sample reached the highest strength when tensile at 150 °C, which was attributed to the hindrance of the basal dislocation and non-basal dislocation slip by the prismatic β' phases and the newly formed basal γ' precipitates.