铝合金7075­T651动态流变应力特征及本构模型

摘要

为了研究铝合金7075­T651的流变应力变化特征，在高温分离式霍普金森压杆装置上对圆柱试样进行了温度范围25~400℃及应变率范围600~12000 s−1的动态压缩试验。结果表明：铝合金7075­T651的流变应力对应变率不敏感，对温度有较强的敏感性。总体上，流变应力随温度的升高而减小，但在350~400℃时流变应力差别很小。在高应变速率时，当应变超过一定水平时，应力出现急剧减小，材料发生失效。通过变形后试样的微观组织观察可以发现，应变速率较高时出现绝热剪切带是材料流变应力急剧减小的主要原因。在实验数据基础上，建立了一个基于物理概念的铝合金7075­T651本构模型预测其流变应力，与实验对比表明，所建立的本构模型在较宽的温度和应变速率范围内能够很好地预测铝合金7075­T651的流变应力。%To understand the flow stress characteristics of aluminum 7075­T651, dynamic compression tests during the temperature range of 25−400℃and strain rate range of 600−12 000 s−1 were performed on cylindrical samples using SHPB technique. The results show that the flow stress of aluminum 7075­T651 is strongly sensitive to temperature compared with strain rate, the flow stress reduces with the increase of temperature. There is a temperature range between 350−400℃where the flow stress doesn’t depend on temperature, showing little difference. At high strain rate when the strain exceeds one certain level, the flow stress decreases sharply and the sample fails. Through the observation of cross­section microstructure of deformed sample, the shear band is responsible for the rapid reduction of flow stress. Finally based on experimental data, a physically based constitutive model is given to depict the flow stress of the aluminum. The model predictions are compared with the results of experiments. Good agreement between the theoretical predictions and experimental results is obtained. The given constitutive model can predict the flow stress of aluminum 7075­T651 in a wide range of temperatures and strain rates.