Effect of tool size on AA6061‐T6 double‐sided friction stir welds

The present work investigates the effects of tool size on microstructural evolution, tensile strength, and microhardness on double‐sided friction stir welding of 12.7‐mm‐thick AA6061‐T6 plates. Three different tools were designed having pin diameters equal to pin lengths of 6.25, 7.5, and 8.5 mm and corresponding shoulder diameters of 18.75, 22.5, and 24.5 mm, respectively. The welds obtained with these three tools were designated as Welds A, B, and C, respectively. Results showed the highest tensile and yield strength for Weld B. The tensile fracture appearance of Welds A and B indicated reasonable necking with crack initiation and propagation through heat affected zone on the advancing side of the weld. However, in the Weld C, fracture appeared in the stir zone near the confluence of thermo‐mechanically affected zone. Electron back scatter diffraction indicates dominance of high angle grain boundaries and major shear textures C and B/B¯ components which corresponds to {001} , 11¯2 , and 1¯12¯< 1¯1¯0> textures in the weld nugget.