应变速率对AM80镁合金压缩变形行为的影响Influence of strain rate on compression deformation behavior of AM80 magnesium alloy

在应变速率分别为0.4、0.07、0.01、0.001、0.0001和0.00003 s^-1，对固溶态AM80镁合金室温不同应变速率下的压缩变形行为及组织演变进行研究。结果表明：实验用AM80镁合金的压缩流变应力在低应变时对应变速率不敏感，而在高应变时则表现出负的应变速率敏感性。极限强度随应变速率的增加逐渐降低，而屈服强度对应变速率不敏感。在变形的第二阶段，由于孪晶的持续产生，增加了AM80镁合金的应变硬化能力，使得应变硬化率在此阶段出现平台。高应变速率(0.4 s^-1)下压缩时的孪晶密度明显高于低应变速率(0.00003 s^-1)下压缩时的孪晶密度，孪生的这种正应变速率敏感性导致应变硬化率在第二阶段随应变速率的增加逐渐由缓慢下降转变为上升。压缩裂纹在应力最为集中的压缩表面边缘形核，然后沿最大剪切应力方向扩展。孪晶和微裂纹是影响裂纹扩展的两个重要因素，两者共同作用导致裂纹出现一定偏折。

The compression deformation behavior and the corresponding evolved microstructure on solution treated AM80 magnesium alloy at different strain rates of 0.4, 0.07, 0.01, 0.001, 0.0001 and 0.00003 s^-1 were investigated at room temperature. The results show that the flow stress is scarcely sensitive to strain rates at low strain level, while it exhibits obvious negative strain rate sensitivity at high strain level. With increasing strain rates, the ultimate strength decreases, while the yield strength is insensitive. The strain hardening capacity increases at stage 2 due to the continuous formation of twins, which results in a plateau on the strain hardening rate curves. Compared with low strain rate (0.00003 s^-1), a significant higher density of twins at high strain rate (0.4 s^-1) shows evident positive strain rate sensitivity for twin, leading the strain hardening rate change from slow decline to increment at stage 2. The cracks nucleate at the compressed surface edge with high stress concentration, and then, propagate along the direction of maximum shear stress. Furthermore, twins and microcracks have strong effect on the propagation of cracks, the interaction of which make the crack appear certain tortuous.

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