5A90铝锂合金超塑性变形的组织演变及变形机理

Microstructural Evolution and Deformation Mechanism of 5A90 Al-Li Alloy During Superplastic Deformation

采用光学显微镜、扫描电镜、电子背散射衍射以及高温拉伸实验研究了工业化制备的5A90铝锂合金超塑性板材变形过程中的组织演变及变形机理。结果表明:在高温拉伸前对板材进行450℃/30min再结晶退火后,在温度为475℃、应变速率为8×10-4s-1的适宜超塑性变形条件下,可使伸长率由原始状态的480%提高至880%。整个超塑性变形过程展现出不同的变形机制:初始阶段(ε≤0.59),板材以形变组织为主,晶粒取向差逐渐增大,位错运动为该阶段的主要变形机制。当真应变达到0.59时,动态再结晶开始发生,晶粒取向差继续增大,晶界滑动开始启动。当真应变大于1.55时,晶粒继续长大,但长大幅度不大且保持等轴状,该阶段变形机制以晶界滑动为主。

The microstructural evolution and deformation mechanism of 5A90Al-Li alloy sheets during superplastic deformation were studied by optical microscopy,scanning electron,electron back scattering diffraction and high temperature tensile test.The results show that the elongation of the specimen,which is recrystallized at 450℃for 30 min before the tensile test,could increase from 480%to880%at an appropriate superplastic condition of 475℃/8×10-4s-1.The superplastic mechanisms of5A90Al-Li alloy sheets are explored by investigating the microstructural evolution.The misorientation increases and dislocation activity plays a key role at the initial stage(ε≤0.59).Dynamic recrystallization begins to occur when the true strain reaches 0.59.With recrystallization,the misorientation between grains becomes larger and grain boundary sliding(GBS)starts at this stage(0.59<ε<1.55).With larger true strains(ε≥1.55),grain continues to grow with a stable microstructure,and superplastic mechanism is dominated by GBS.