Abstract: In the post-weld heat treatment process, the fine recrystallized grains in the weld nugget area of the friction stir welded joints are extremely unstable at high temperatures, and abnormal grain growth is prone to reduce joint performance. Research on the microstructural thermal stability of 2024 aluminum alloy and 7075-2024 aluminum alloy friction stir welded joints, the results found that: increasing the rotational rate and reducing the welding speed are beneficial to improve the microstructural thermal stability of the joint, and the smaller the difference in grain size in the weld nugget, the smaller the particle size of the second phase, the greater the density, and the better the thermal stability of the joint structure; lowering the solution temperature or shortening the solution time can reduce the abnormal grain growth, but the mechanical properties of the joint are decreased. For the 3 mm thick 2024 aluminum alloy friction stir welded joint, with the welding parameters of ω=2 500 r/min, v=20 mm/min, there is no obvious abnormal grain growth of the joint after solution treatment at 495 ℃-30 min. For the 1.5 mm thick 7075-2024 aluminum alloy friction stir welded joint, with the welding parameters of ω=2 500 r/min, v=50 mm/min, the abnormal grain growth of joint after the solution treatment at 450 ℃-20 min is basically controlled. The joint strength reaches 90% of the base material. The research results obtain a good effect of inhibiting abnormal grain growth, which provides a reference for the control of the structure and performance of aluminum alloy friction stir welded joints.

Key words: aluminum alloy, friction stir welding, microstructural thermal stability, abnormal grain growth