Abstract
The influence of seven different tool pin profiles was investigated to appraise the tensile, flexural strength, fracture behavior, and microstructure evolution in friction stir welded similar AA6061-T6 joints. Results indicate that each tool pin profile affects the material flow/intermixing in different ways; consequently, the weld nugget feature and grain size in the stir zone (SZ) were also observed to be different. Relatively finer grains with homogenous microstructure in SZ were observed for joints prepared using cylindrical grooved with straight flutes (CGF) and cylindrical grooved (CG) tool pins. The highest tensile strength and flexural load were observed for joints obtained with CGF tool pin followed by CG tool pin. A relationship between average yield strength of the joint and inverse square root of average SZ grain size was established for these joints. EBSD analysis revealed that the SZ is the mixture of low angle grain boundaries and high angle grain boundaries (HAGBs) and the fraction is controlled by different pin profiles. The HAGBs and high shear texture components B/B¯ and C were found predominant in welds prepared with CGF and CG tool pins. Fractographic analyses showed the presence of numerous dimples in sound bonded regions indicating the ductile fracture; however, tearing/rupture and shear failure were witnessed near the vicinity of the tunnel region.
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