物理概念的本构关系
(西北工业大学 航空学院，西安 710072)
摘 要: 利用准静态试验机以及Hopkinson压杆装置对AZ31铸造镁合金在不同应变速率和不同温度下的塑性流动性能进行研究，结合金相显微技术对试验后的试样进行微观分析。结果表明：在低应变速率下，随着温度的升高，AZ31镁合金发生明显的由脆性到韧性的转化，其转化温度为473 K左右；当应变速率增加到1.2×104 s−1时，会发生脆化现象，塑性变形能力变差。基于微观分析，低应变速率下晶体中孪晶的存在是促进材料塑性变形增加的主要因素。而在高应变速率下，动态再结晶和第二相粒子沉淀硬化显著地影响金属的塑性变形。结合系统的试验结果，基于热激活位错机制，建立一种物理概念的塑性流动本构模型，对较高应变速率和不同温度下的流动应力进行模型预测。通过对比，模型预测结果与试验数据吻合较好。
关键字: AZ31镁合金；塑性流动；应变速率；微观机理；本构关系
constitutive relation for AZ31 cast magnesium alloy
（School of Aeronautics, Northwestern Polytechnical University, Xi’an 710072, China）
Abstract:The plastic flow properties of cast magnesium alloy AZ31 were studied at different strain rates and temperatures by using quasi-static testing machine and Hopkinson pressure bar equipment. The microstructure analysis of deformed specimen was carried out by means of the metallography microscope technique. The results show that, at lower strain rates, the transformation of AZ31 alloy from brittleness to toughness occurs with increasing temperature, and the transformation temperature is about 473 K. The brittleness phenomenon happens with increasing strain rate to 1.2×104 s−1, and the plastic deformation capability becomes weak. Based on the microstructure analysis, the key factor of the plastic deformation enhancement at low strain rates is due to the existence of twinning in the crystal. At higher stain rates, however, the dynamic recrystallization and second phase particle precipitation hardness strongly affect the metal plasticity. Based on the thermal activation dislocation mechanism, paralleled with the system testing results, a plastic flow constitutive model with the physical conception was established. The model was used to predict the plastic flow stress at different temperatures and higher strain rates. According to comparing results, good agreement between the model predictions and experimental results is obtained.
Key words: AZ31 magnesium alloy; plastic flow; strain rate; microstructure mechanism; constitutive relation
