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.