Microstructure and Mechanical Property Evolution of Mg-Gd-Y-Nd-Zr Casting Alloy During Aging Treatment
TANG Changping1, 2, LI Guodong3, LI Zhiyun4, SUN Xuanqi4
1 School of Materials Science and Engineering, Hunan University of Science and Technology, Xiangtan 411201; 2 High Temperature Wear Resistant Materials and Preparation Technology of Hunan Province National Defence Science and Technology Laboratory, Xiangtan 411201; 3 Equipment Management Department, Suzhou Nuclear Power Research Institute Company Limited, Shenzhen, 518124; 4 Science and Technology Company Limited of No. 608 Research Institute, Zhuzhou, 412002
Abstract: Microstructure and mechanical property evolution of Mg-Gd-Y-Nd-Zr casting alloy during aging treatment were investigated by means of optical microscopy (OM), hardness testing, uniaxial tensile testing, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicated that the alloy exhibited good ductility and low strength after solution treatment, and the elongation exceeded 10%. As the aging time prolonged, the strength increased while the ductility decreased. The sample was in under-aged state when treated at 225 ℃ for 3 h, and β″was the main strengthening phase, which was coherent with the matrix. The fracture surface of the sample featured cleavage planes, dimples, tea-ring ridges and grain boundaries. In the peak-aged state, the strengthening phase was β', which is semi-coherent with the matrix. The ultimate tensile strength of the peak-aged sample exceeded 300 MPa, while the ductility decreased sharply. The fracture surface of the sample featured cleavage planes, tearing ridges and grain boundaries. The proportion of cleavage planes was obviously higher than that in under-aged sample, and the cleavage plane and the grain boundary were smooth. The strength increased but the ductility decreased when the sample was over-aged. Grain boundaries and cleavage planes were the main characterization of the fracture surface.
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2018, Vol. 32 
