应变速率对AZ61镁合金动态再结晶行为的影响

Influence of strain rate on dynamic recrystallization behavior of AZ61 magnesium alloy

采用光学显微镜、SEM/EBSD和组织定量分析技术研究AZ61镁合金在623 K、3×10-5~3×10-1 s-1下单向压缩时变形和动态再结晶行为。结果表明：AZ61镁合金的流变应力和动态再结晶行为强烈地受到应变速率的影响;随着应变速率的提高,稳态流变应力对应变速率的敏感性逐渐减弱,而峰值应力对应变速率的敏感性却呈先减弱后又显著增强的趋势。提高应变速率可加快动态再结晶进程,但高速变形初期产生更多的粗大{1012}孪晶,不利于完全再结晶而导致稳态时的再结晶体积分数反而较低;在中低应变速率下动态再结晶以晶界弓出形核为主,而在高应变速率下则主要通过孪晶分割来进行;由应变速率引起变形机制的变化是导致不同动态再结晶行为的原因。

The deformation and dynamic recrystallization behavior of magnesium alloy AZ61 were studied at 623 K and 3×10-5-3×10-1 s-1 by optical and SEM/EBSD metallographic observation.The results show that the flow stresses and the dynamic recrystallization behavior are dependent on strain rates.With the increase of the strain rate,the strain rate sensitivity becomes weaker for steady state stresses while the strain rate sensitivity for the peak stress decreases firstly then increases obviously.Increasing strain rate can accelerate the process of dynamic recrystallization and the development of coarse twins which are harmful to get a complete recrystallization structure leading to the decrease of fractional recrystallization.Bulging mechanism for dynamic recrystallization nucleation operates mainly at lower strain rate,whereas the dynamic recrystallization substructure developed at higher strain rate is characterized by twin intersections.The difference of deformation mode leads to the operation of different mechanisms of dynamic recrystallization nucleation.