Effect of rotation speed to welding speed ratio on microstructure and mechanical behavior of friction stir welded aluminum-lithium 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 T ₁ 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. The ratio of rotation speed to welding speed (ω/ν) has great impact on the joint microstructure and menchanical properties. As the value of ω/ν increases from 2 to 4, the shape of the WN changes as well as the area of the WN increases. For ω/ν = 2, both sides of the "traperzoid" are slightly concave while as ω/ν = 4, both sides of "traperzoid" are slightly convex. Besides, with increasing ω/ν the microhardness of the joints decreases.