Friction stir welding of mild steel to alloy 625-development of welding parameters

Friction stir welding parameters were developed for a 6 mm thick dissimilar butt joint made of mild steel and Ni based alloy 625. A composite W-Re/polycrystalline cubic born nitride tool was used to study the effect of tool offset (between 0 and 3.13 mm away from the alloy 625 plate) and rotational speed (between 250 and 350 rev min(-1)) on joint consolidation. When non-optimal parameters were used, macrovoids were observed at the advancing side and faying surface near the joint interface root. Defect free joints were obtained using 300 rev min(-1), 100 mm min(-1), tool offset of 1.63 mm, and axial force between 25 and 30 kN, under force controlled mode.