Effect of Pre- and Post-Weld Heat Treatment on Microstructure and Properties of 2195 Al-Li Alloy Double-Sided Friction Stir Welded Joints

6 mm thick 2195 aluminum-lithium alloy plates were connected by double-sided friction stir welding. The effects of pre- and post-weld heat treatment(410 ℃×1 h annealing + 510 ℃×1 h solution and 155 ℃×1 h artificial aging) on the microstructure and mechanical properties of joints were compared and studied. The results show that the grains in the weld nugget area of the joint with pre-weld heat treatment were small and equiaxed, and the average grain size was about 9.2 μm. The grains in the weld nugget area with post-weld heat treatment grew abnormally, and the average grain size reached 0.3 mm. The tensile strength of the joint with pre-weld heat treatment was about 4.7% higher than that with post-weld heat treatment, and the percentage elongation after fracture was improved obviously. The tensile fracture mode of the joint with pre-weld heat treatment was ductile fracture, and that with post-weld heat treatment was brittle fracture. The maximum bending angle of the joint with pre-weld heat treatment was larger than the joint with post-weld heat treatment, indicating the joint had good plastic deformation ability.