AZ31镁合金热变形流动应力预测模型

采用近等温单轴压缩实验获得了AZ3l镁合金变形温度为523 723 K,应变速率为0.01—10 s^-1条件下的流动应力,分析了变形温度和应变速率对流动应力的影响规律.结果表明,AZ31镁合金变形过程中发生了动态再结晶,523 K时形成细小组织;而723 K时动态再结晶和长大的晶粒沿径向拉长.考虑实验过程塑性变形功和摩擦功引起的温度升高,在高应变速率条件下采用温度补偿修正了流动应力.在此基础上,建立了基于双曲正弦模型的峰值流动应力和统一本构关系,该模型利用材料参数耦合应变来描述流动应力的应变敏感性,进一步获得了合金热变形过程中流动应力与变形温度、应变速率和应变的定量关系.采用该本构关系模型预测流动应力具有较高的精度,预测值与实测值相关系数为0.976,平均相对误差为5.07%,实验条件范围内预测的流动应力与实验值几乎能保持一致.

PREDICTED CONSTITUTIVE MODELING OF HOT DEFORMATION FOR AZ31 MAGNESIUM ALLOY

The uniaxial compression tests of AZ31 magnesium alloy at different strain rates of 0.01—10 s^-1 and different deformation temperatures of 523—723 K were performed by using Gleeble- 1500 simulator with a maximum strain of 0.916.The influences of deformation temperature and strain rate on the flow stress were investigated.The fine microstructure is attributed to dynamic recrystallization during compression process at 523 K.The stretched grains of dynamic recrystallization and growth up along radial direction were founded in microscopic observation at 723 K.Considering plasticity deformation and friction induced temperature rise,the flow stress was corrected at high strain rate by using temperature compensation.The peak flow stress and unified constitutive model were established based on hyperbolic sine model.Strain sensitivity of flow stress was studied to describe the coupling of materials parameters on the strain,and then the relationship between deformation temperature,strain rate and strain during hot deformation was obtained.Comparing with experimental results,the correlation coefficient and average relative error of predicted and measured values are 0.976 and 5.07%respectively,it is proved that the model reflects the real deformation feature of the AZ31 magnesium alloy.