應變速率對AM80鎂合金壓縮變形行為的影響Influence of strain rate on compression deformation behavior of AM80 magnesium alloy

在應變速率分別為0.4、0.07、0.01、0.001、0.0001和0.00003 s^-1，對固溶態AM80鎂合金室溫不同應變速率下的壓縮變形行為及組織演變進行研究。結果表明：實驗用AM80鎂合金的壓縮流變應力在低應變時對應變速率不敏感，而在高應變時則表現出負的應變速率敏感性。極限強度隨應變速率的增加逐漸降低，而屈服強度對應變速率不敏感。在變形的第二階段，由于孿晶的持續產生，增加了AM80鎂合金的應變硬化能力，使得應變硬化率在此階段出現平臺。高應變速率(0.4 s^-1)下壓縮時的孿晶密度明顯高于低應變速率(0.00003 s^-1)下壓縮時的孿晶密度，孿生的這種正應變速率敏感性導致應變硬化率在第二階段隨應變速率的增加逐漸由緩慢下降轉變為上升。壓縮裂紋在應力最為集中的壓縮表面邊緣形核，然后沿最大剪切應力方向擴展。孿晶和微裂紋是影響裂紋擴展的兩個重要因素，兩者共同作用導致裂紋出現一定偏折。

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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