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
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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 18R long-period stacking ordered (LPSO) phases with a composition of Mg10ZnY 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.
Keywordsmagnesium alloys ingots homogenization microstructural evolution mechanical properties
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This work is supported by the Youth Science Fund Project of the National Natural Science Fund of China (No. 51401070), the Program for New Century Excellent Talents in Universities (No. NCET-12-0849), and the Fundamental Research Funds for the Central Universities (No. 2014ZZD03).