5A90铝锂合金的超塑性变形行为

摘要

采用光学显微镜、电子背散射衍射、电导率测试以及超塑性高温拉伸实验研究5A90铝锂合金超塑性变形行为和变形机理.研究结果表明:经450℃/30 min再结晶退火后,在变形温度为500℃、应变速率为8×10?4s?1的超塑性变形条件下,可使伸长率由未退火状态的630%提升至1120%;在超塑性变形过程中,晶粒由长条状逐渐变为等轴状,而退火后的晶粒更加细小且等轴化程度更高,再结晶退火还可以提高材料内部的空位浓度并增加大角度晶界所占的比例,这都有利于伸长率提高;在最适宜超塑性变形条件下,该材料的应变速率敏感性指数m为0.63,因此,其主要变形机制为晶界滑移,但在变形后期扩散机制成为一种协调机制.%The superplastic deformation behavior and deformation mechanism of 5A90 Al-Li alloy during superplastic deformation were studied by optical microscopy, electron back scattering diffraction, electrical conductivity test 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 can increase from 630% to 1120% at an appropriate superplastic condition, which is obtained at temperature of 500℃ and an initial strain rate of 8×10?4s?1. During the process of superplastic deformation, elongated grains gradually change to be equiaxed, and after annealing grain size becomes smaller and axis degree is higher. In addition, recrystallization annealing can improve vacancy concentration and increase the proportion of large angle grain boundary, which is beneficial to the improvement of the elongation. In the appropriate condition, the strain rate sensitivity indexm of thismaterial is 0.63, and the main deformation mechanism is GBS. But at the late stage of the deformation, diffusion is taken as a coordination mechanism.