AZ31连铸板的高温压缩变形行为及组织演变

High Temperature Compression Deformation Behavior and Microstructure Evolution of AZ31 Continuous Casting Plate

摘要:

合金在高温下的流变应力与组织演变特征是构建合金热加工参数的重要基础。基于此，利用Gleeble 1500D对AZ31连铸板在温度为450和500 ℃、应变速率为0.15 s^-1的压缩行为进行了研究，并将其与400 ℃及以下温度的压缩变形行为进行了对比。结果发现：随着温度的升高，合金的稳态流变应力值下降，在500 ℃进行35%变形时仅约28.2 MPa；在较低温度时，合金流变应力取向差异（0 °试样＜5 °试样＜10 °试样）随温度升高而消失；不同于稳态流变应力的变化，再结晶比例则随变形温度的升高而增大，变形量与再结晶比例之间保持正相关，而取样角度使得再结晶比例的取向性较强，500 ℃时再结晶比例在不同取样方向上遵循0 °试样＜5 °试样＜10 °试样的变化趋势；随着变形量的进行，动态再结晶越来越充分，其组织形貌逐渐由晶界处的零散分布再结晶晶粒向“项链状”再结晶分布转变，并且逐渐呈包围状态向晶体内部扩展，最后完全取代原始连铸板组织。此外，通过示意图的方式再现了合金再结晶的形核与长大过程。

Abstract:

The characteristics of flow stress and microstructure evolution of an alloy at high temperature are important bases for constructing hot working parameters of the alloy. Based on this， the compression behavior of AZ31 continuous casting plates at 450 ℃ and 500 ℃ with the strain rate of 0.15 s^-1 were studied using Gleeble 1500D， and compared with the compression deformation behavior of magnesium alloy at 400 ℃ and below. The results showed that as the temperature increased， the steady-state flow stress of alloy decreased， and when subjected to 35% deformation at 500 ℃， it was only about 28.2 MPa. The flow stress of samples from different sampling directions showed a variation trend of 0 °<5 °<10 ° at 450 ℃， and the trend disappeared with temperature increase to 500 ℃. Unlike the change in steady-state flow stress， the recrystallization fraction increased with the increase of deformation temperature， and there was a positive correlation between deformation and recrystallization fraction. The sampling angle made the orientation of the recrystallization fraction stronger. At 500 ℃， the recrystallization fraction of samples from different sampling directions followed the trend of 0 °<5 °<10 °. As the deformation progressed， dynamic recrystallization became more and more complete， and its microstructure gradually transformed from scattered recrystallized grains at grain boundaries to a "necklace-like" recrystallization distribution， gradually expanding into the interior of the grain， and finally completely replacing the original continuous casting plate microstructure. In addition， the nucleation and growth process of alloy recrystallization were reproduced through a schematic diagram.