Effects of Friction Stir Welding Process Parameters on Welded Seam Forming and Mechanical Properties of Welded Joint for 2198 Al-Li Alloy

The friction stir welding test was performed on 2198 Al-Li alloy sheet, and the effects of rotation rate and welding rate of friction stir tool on welded seam forming and mechanical properties of welded joint were analyzed. The results show that when the ratio of rotation rate to welding rate was more than 15.7, a compact welded seam with good forming surface and free of defects was obtained. The microstructure in nugget zone was fine equiaxed grains, and the microstructure of heat-mechanical affected zone at advancing side was almost small equiaxed grains, and the lath structure of heat-mechanical affected zone at the retreating side deformed, there were small grains around the lath microstructure. The tensile strength of the joints decreased with the increase of rotation rate when the welding rate was 30 mm·min-1, and the maximal tensile strength was 432.17 MPa. The hardness of the welded seam was lower than that of the base metal, and the hardness of nugget zone was little higher than that of heat-mechanical affected zone, and the hardness of heat-mechanical affected zone was the lowest. The softened range of heat affected zone became wider with the increase the ratio of rotation rate to welding rate.