Effects of aging treatment processes on microstructures and mechanical properties of AZ63 casting magnesium alloy

The effects of three different aging treatment processes,namely single-stage,double-stage,and reverse double-stage aging treatment processes,on the microstructures and mechanical properties of the AZ63（Mg-6Al-3Zn-0.25Mn） casting magnesium alloy were investigated and compared.The results indicate that the microstructures of all the aged alloys under the three treatment processes are mainly composed of α-Mg,Mg17Al12), and Al4Mn phases,indicating that the double-stage and reverse double-stage aging treatments have no obvious effect on the type of alloy phases.However,as compared with the single-stage and double-stage processes,the reverse double-stage process has a great effect on the quantity of the Mg17Al12 phases.After the reverse double-stage aging treatment,which results in a stronger drive for decomposition of the supersaturated solid solution,the number of Mg17Al12 phases precipitated in the grains significantly increases.In addition,as compared with the single-stage aged alloy,the tensile properties at room temperature for both the double-stage and reverse double-stage aged alloys are significantly improved.Among them,the reverse double-stage aged alloy achieves the highest tensile strength,yield strength,and elongation of 295 MPa,167 MPa,and 8.6%,respectively.