Mg-8Gd-0.5Zr合金热压缩过程中动态再结晶行为

Dynamic Recrystallization Behavior of Mg-8Gd-0. 5Zr Alloy During Hot Compression Deformation

将Mg-8Gd-0.5Zr合金在350~500℃、应变速率为0.002~1s^-1范围内进行热压缩实验,研究合金的流变应力行为,观察热压缩后的组织,分析动态再结晶晶粒尺寸和温度的关系,并利用加工硬化率的方法计算合金的再结晶临界应变(εc)。结果表明:Mg-8Gd-0.5Zr合金热压缩流变曲线符合动态再结晶的特征,随着温度升高或者应变速率的减小,峰值应力下降,且峰值应力对应的峰值应变(εp)也降低。在350~450℃范围内,再结晶晶粒细小,且其随温度升高增长较慢;而温度在450~500℃范围内,再结晶晶粒尺寸迅速长大至约25μm。根据加工硬化率的计算及组织分析,发现动态再结晶先于峰值应变发生,峰值应变和临界应变的关系为εc=0.442εp,同时构建了再结晶的临界模型。

The hot deformation behaviors of Mg-8Gd-0.5Zr was studied by hot compression tests in the temperature range of 350-500 ℃ under strain rates of 0.002-1 s ^-1 . The flow stress and microstructures of the alloy were discussed. The relationship between grain size of dynamic recrystallization (DRX) and temperature were analyzed. The critical strain (ε c) of DRX was calculated. Results showed that the flow stress curves conformed to the characteristic of dynamic recrystallization. The peak stress decreased as the temperature increased or the strain rate decreased,and the peak strain (ε p) also decreased. The dynamically recrystallized (DRXed) grains were fine in the range of 350-450 ℃,and the grain size increased slowly but increased rapidly in 450-500 ℃. The grain size of DRX was 25 μm after hot compression in 500 ℃. According to calculation of work hardening rate,it was found that the DRX occured prior to peak strain. The relationship between peak strain and critical strain was ε c=0.442 ε p. The critical model of recrystallization was established.