Influence of forging action on the microstructural and mechanical characteristics of the friction stir welded joints of aluminum alloy with varied joint configurations

The variation in the forging action during single-side friction stir welding (SS-FSW) and double side friction stir welding (DS-FSW) joining of AA-6061 T6 alloy by friction stir welding (FSW) process was conducted. The microscopic study of the stir zone (SZ) of SS-FSW joint configurations showed that the forging action obtained with a 3° tool tilt angle (TTA) provided better intermixing of material, with significant downward and inclined flow of plasticized material under the shoulder interaction zones. This led to the maximum grain refinement as compared to the forging action obtained with 0° and 2° TTA. For DS-FSW joint, a good interlocking between the material stirred during the first and second pass was observed, which led to maximum joint efficiency, and the elimination of the problem of insufficient root penetration observed during the SS-FSW. The misorientation analysis revealed that the percentage of high angle grain boundaries (HAGBs) significantly increased for DS-FSW joint due to the small thermal gradient along the plate thickness. Moreover, the dominance of B/ B ¯ shear texture with sufficient dissimilarity in the crystallographic orientation to the random texture was observed within the SZ of DS-FSW joint.