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Hot Deformation Behavior of az40 magnesium alloy at Elevated Temperatures

Journal of Wuhan University of Technology(Materials Science) 2017年第6期32卷 1470-1475页

作者：赖林张奎 MA Minglong LI Xinggang LI Yongjun SHI Guoliang YUAN Jiawei State Key Laboratory for Fabrication and Processing of Nonferrous Metals Beijing General Research Institute for Nonferrous Metals

Hot compression tests on az40 magnesium alloy were conducted on a Gleeble 1500 d hot simulation testing machine in a deformation temperature range of 330 ℃-420 ℃ and a strain rate range of 0.002-2 s^-1. Hot deformation behaviors were investigated on the basis of the analysis of the flow stressstrain curves, constitutive equation, and processing map. The stress exponent and apparent activation energy were calculated to be 5.821 and 173.96 k J/mol, respectively. Deformation twins and cracks located in grain boundaries were generated at 330 ℃ and 0.02 s^-1, which are associated with a high strain rate and a limited number of available slip systems. With increasing temperature and decreasing strain rate, the twins disappeared and the degree of dynamic recrystallization increased. The alloy was completely dynamically recrystallized at 420 ℃ and 0.002 s^-1, with a homogenous grain size of approximately 13.7 μm. The instability domains of the deformation behavior can be recognized by processing maps. By considering the processing maps and characterizing the microstructure, the optimum hot deformation parameters in this experiment were determined to be 420 ℃ and 0.002 s^-1.

关键词： az40 magnesium alloy hot compression processing map recrystallization

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Mixed grain structure and mechanical property anisotropy of az40 magnesium alloy bar with diameter of 160 mm

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Transactions of Nonferrous Metals Society of China 2015年第12期25卷 3944-3952页

作者：石国梁张奎李兴刚李永军马鸣龙袁家伟卢春芳北京有色金属研究总院有色金属材料制备加工国家重点实验室北京100088

The mixed grain structure and mechanical property anisotropy of az40 magnesium alloy bar with a diameter of 160 mm manufactured by ＂multi-direction forging（MDF）＋ extrusion ＋ online cooling＂ technique were investigated by optical microscopy（OM）, scanning electron microscopy（SEM）, X-ray diffraction macro-texture measurement and room temperature（RT） tensile test. The results show that mixed grain structure is caused by the micro-segregation of Al in semi-continuous casting ingot. Homogenization of（380 °C, 8 h）＋（410 °C, 12 h） cannot totally eliminate such micro-segregation. During MDF and extrusion, the dendrite interiors with 3%-4% Al（mass fraction） transform to fine grain zones, yet the dendrite edges with about 6% Al transform to coarse grain zones. XRD macro-textures of the outer, R/2 and center show typical fiber texture characteristics and the intensity of [0001]//Ra D orientation in the outer（11.245） is about twice as big as those in the R/2（6.026） and center（6.979）. The as-extruded az40 magnesium alloy bar has high elongation（A） and moderate ultimate tensile strength（Rm） in both extrusion direction（ED） and radius direction（Ra D）, i.e., A of 19%-25% and Rm of 256-264 MPa; however, yield strength（Rp0.2） shows anisotropy and heterogeneity, i.e., 103 MPa in Ra D, 137 MPa in ED-C（the center） and 161 MPa in ED-O（the outer）, which are mainly caused by the texture.（155 °C, 7 h）＋（170 °C, 24 h） aging has no influence on strength and elongation of az40 magnesium bar.

关键词： az40 magnesium alloy mixed grain structure mechanical properties anisotropy micro-segregation texture

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