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

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℃×24 h+200℃×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℃ peak-aging(200PA)and 250℃ peak-aging(250PA)samples were different with the increasing tensile tenperature.When tensile test processed at 150℃,the denseβ’phase and rod-shaped basalγ’phase will be formed in the 200PA sample.However,at 300℃,theβ’phases disappeared.Theβ’and LPSO phases in the 250PA sample coarsened gradually as the tensile temperature increased,and 14H-LPSO phases were formed during tensile at 300℃.The 200PA sample reached the highest strength when tensile at 150℃,which was attributed to the hindrance of the basal dislocation and non-basal dislocation slip by the prismaticβ’phases and the newly formed basalγ’precipitates.