力学失配FSW接头拉伸变形的光学原位分析

Optical in situ analysis of tensile deformation of mechanical mismatched FSW joint

关键词:  原位拉伸|高配接头|低配接头|裂纹扩展

Key words:  in situ tensile test|high-matched joint|low-matched joint|crack growth

摘要:

采用光学原位拉伸试验对2A12-T4和2A12-O铝合金搅拌摩擦焊接头在拉伸变形过程中的微观损伤演变进行了观察，并分析了失配接头的裂纹扩展路径. 结果表明，2A12-O高配接头拉伸试验断裂于母材，2A12-T4低配接头断裂于近HAZ区；高配和低配接头第二相粒子与母材晶粒性能均不匹配，导致低配接头裂纹多萌生于第二相粒子，且较大的第二相粒子开裂程度明显大于较小第二相粒子和基体，而高配接头裂纹多萌生晶粒内；高配接头和低配接头裂纹扩展路径均以穿晶扩展为主，高配接头中的微裂纹、大角度晶界和第二相粒子对裂纹的扩展起到阻碍作用，低配接头破裂的第二相粒子对裂纹的扩展起到促进作用.

Abstract:

The microscopic damage evolution of 2A12-T4 and 2A12-O aluminum alloy friction stir welding during tensile deformation was observed by optical in-situ tensile tests, and the crack growth path of the mismatched joints was analyzed. The results show that the fracture of the 2A12-O high-matched joint in the tensile test is in the base material, while that of the 2A12-T4 low-matched joint is near the HAZ zone.The second phase particles of high-matched joints and low-matched joints are not matched with the grain properties of the base material, which leads to the fact that the cracks of low-matched joint are mostly generated from the second phase particles, and the cracking degree of the larger second-phase particles is obviously greater than that of the smaller ones and matrix, while the cracks of high-matched joint are mostly generated inside the grains. The crack propagation paths of both the high-matched and the low-matched joints are mainly transgranular propagation. The microcrack, large-angle grain boundary and second-phase particles in the high-matched joints hinder the crack propagation, while the broken of second phase particles in the low-matched joints can promote the crack growth.