Effect of Rotation Speed to Welding Speed Ratio on Microstructure and Mechanical Behavior of Friction Stir Welded Aluminum– L ithium Alloy Joints

2198 Al–Li alloy welds were performed by friction stir welding (FSW) to investigate the influence of the ratio of rotation speed to welding speed (ω/ν) on joint microstructure, microhardness, and tensile properties. Transmission electron microscopy (TEM) was used to reveal the precipitate type across the weld cross‐section. Results show that ω/ν has a little impact on both macroscopic morphology and microstructure of joints. Dissolution of precipitates has occurred in the weld nugget (WN). The density of T1 phase and its size in the WN decrease remarkably. Changes to the T1 phase are linked to a significant reduction in microhardness across the weld. With increasing ω/ν the microhardness of the joints decreases. The value of ω/ν also has impact on the fracture mode of the joints as well as the elongation.