Solid solution behavior, microstructure and properties of Mg-9Gd-0.8Al alloy solidified at different cooling rates
ZHANG An-guo1, REN Guang-xiao2, GUAN Zhong1, LUO Pei-lin3, WANG Hong-xia1, NIU Xiao-feng1
1. College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, Shanxi, China; 2. Technical Research and Development Department, Shanxi Jianghuai Heavy Industry Co., Ltd., Jincheng 048000, Shanxi, China; 3. College of Software, Taiyuan University of Technology, Taiyuan 030024, Shanxi, China
Abstract：In order to explore the effect of Al element on the microstructure refinement of Mg-9Gd alloy under different cooling rates and its influence on the subsequent solid solution treatment, the as-cast Mg-9Gd-0.8Al was prepared by gravity casting with iron and copper mold, followed by 10-50 h solid solution treatment. The effect of cooling rate on the solidification, solid solution behavior, microstructure and mechanical properties of Mg-9Gd-0.8Al alloy was studied by OM, SEM, TEM, EDS and XRD. The results show that the microstructure of as-cast Mg-9Gd-0.8Al alloys prepared by iron mold and copper mold are all composed of α-Mg matrix, petal-like (Mg, Al)3Gd phase, thin strip-like Mg5Gd phase and square-like Al2Gd phase. The cooling rate of copper mold is faster than that of iron mold, so the grains and the second phases of alloy are significantly refined, and the total volume fraction of the second phase increases by 56.1%. After the alloys prepared by the two molds are solid solutioned for 10 h, the Mg5Gd phase is dissolved, the (Mg, Al)3Gd phase is partially dissolved, high melting point Al2Gd phase remaines unchanged and the intragranular lamellar (Mg, Al)2Gd phase precipitates. The total volume fraction of the second phases tends to be the same. After 50 h of solid solution treatment, the lamellar (Mg, Al)2Gd phase is dissolved and the residual (Mg, Al)3Gd phase fuses to be particle-like, the particles of alloy prepared by copper mold are smaller than those of iron mold. Grain refinement strengthening and second phase strengthening greatly improve the properties of as-cast alloys prepared by copper mold compared with alloys prepared by iron mold. After 10 h of solid solution treatment, the yield strength of alloy is improved, while the elongation remain unchanged. After 50 h of solid solution treatment, solid solution strengthening, grain refinement strengthening and second phase strengthening of fine second phase particles make the alloy prepared by copper mold obtain best properties, yield strength, ultimate strength and elongation are 141 MPa, 234 MPa and 22.4%, respectively.
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2022, Vol. 32 
