Underlying reasons of poor mechanical performance of thick plate aluminum-copper alloy vacuum electron beam welded joints

As a light-weight and high-strength structural material, aluminum alloy has become an irreplaceable metal material in the aerospace field. In this paper, 25 mm thick Al-Cu alloy (2A12) was welded by electron beam. The welded joints softened leading to the hardness and tensile strength of the joint decreased. In view of the decrease of mechanical properties, the microstructure in different areas of the welded joint was analyzed. At the same time, the formation mechanism of rosaceous microstructures and eutectic structures was revealed. The influence of impurity elements on the joint was analyzed. In addition, the reason of joint strengthening effect weakening was explained combining with welding temperature field and the precipitation model of competition.