Microstructure evolution and mechanical properties of a large-sized ingot of Mg–9Gd–3Y–1.5Zn–0.5Zr（wt%） alloy after a lower-temperature homogenization treatment

Zhi-yong Xue¹，Yue-juan Ren¹，Wen-bo Luo²，Yu Ren¹，Ping Xu³，Chao Xu¹

1. School of Energy,Power and Mechanical Engineering,North China Electric Power University2. School of Materials Science and Engineering,University of Science and Technology Beijing3. College of Science,Rocket Force University of Engineering

摘 要：In this paper,a large-sized ingot of Mg–9Gd–3Y–1.5Zn–0.5Zr（wt%） alloy with a diameter of 600 mm was successfully prepared by the semi-continuous casting method.The alloy was subsequently annealed at a relatively low temperature of 430°C for 12 h as a homogenization treatment.The microstructure and room-temperature mechanical properties of the alloy were investigated systematically.The results show that the as-cast alloy contained a mass of discontinuous lamellar-shaped 18 R long-period stacking ordered（LPSO） phases with a composition of Mg10 Zn Y and an α-Mg matrix,along with net-shaped Mg5（Y,Gd） eutectic compounds at the grain boundaries.Most of the eutectic compounds dissolved after the homogenization treatment.Moreover,the amount and dimensions of the lamellar-shaped LPSO phase obviously increased after the homogenization treatment.The structure of the phase transformed into 14H-type LPSO with composition Mg12Zn（Y,Gd）.The mechanical properties of the heat-treated large-sized alloy ingot are uniform.The ultimate tensile strength（UTS） and tensile yield strength（TYS） of the alloy reached 207.2 MPa and 134.8 MPa,respectively,and the elongation was 3.4%.The high performances of the large-sized alloy ingot after the homogenization treatment is attributed to the strengthening of the α-Mg solid solution and to the plentiful LPSO phase distributed over the α-Mg matrix.

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