AZ31B镁合金热变形开裂准则的研究

Fracture Criterion on Thermal Deformation of AZ31B Magnesium Alloy

以铸态AZ31B镁合金为研究对象,时效处理(400℃/12 h)后,在Gleeble-3800热模拟机上进行了变形温度为250 450℃、应变速率为0.01~10 s^-1的热模拟压缩试验,通过高速摄影技术确定了合金热压缩过程中的临界开裂应变,结合有限元模拟确定了热压缩临界开裂损伤值。结果发现,经典Freudenthal准则能够很好地反映高速摄影技术和热模拟压缩试验观察到的试样表面裂纹萌生以及扩展的现象,结果与金相观察一致。因此,基于Freudenthal准则,通过引入Zener-Hollomon因子来表征镁合金热变形过程的临界开裂损伤值随变形温度和应变速率的变化,建立了适用于铸态AZ31B镁合金的热变形开裂准则。该准则很好地揭示了镁合金热变形的临界开裂损伤值与应力状态、应变、变形温度和应变速率等变形参数之间的关系,为铸态AZ31B镁合金热变形开裂预测提供了理论支撑,为该合金热加工参数的优化奠定了技术基础。

As-cast AZ31B magnesium alloy after homogenization treatment was taken as the research object, and a thermal simulation compression test with deformation temperature of 250~450 °C and strain rate of 0.01~10 s-1 was carried out on the Gleeble-3500 thermal simulator. The critical crack strain in the process of thermal compression was determined by high speed photographic technique, and the critical crack damage value was determined by FEM simulation. The results reveal that the classical Freudenthal criterion can well reflect the phenomenon of surface crack initiation and propagation observed by high-speed photographic technique and thermal simulation compression experiment, and the results are consistent with the metallographic observation. Therefore, based on the Freudenthal criterion,a new fracture criterion was established by introducing the Zener-Hollomon factor to characterize the effect of deformation temperature and strain rate on the critical fracture damage of magnesium alloy during thermal deformation process. The fracture criterion well indicate the relationship between the critical fracture damage value of magnesium alloy and the stress state, strain, deformation temperature and strain rate, which provide a theoretical support for predicting thermal deformation cracking of as-cast AZ31B magnesium alloy and lay the technical foundation for optimizing the parameters of thermal processing of the alloy.