Friction stir lap welding between A6061/SPC270 thin sheets using welding tool with scroll shoulder

Abstract Dissimilar materials welding between A6061 and SPC270 thin sheets was performed through friction stir lap welding and the effects of welding tool shape and clearance were investigated. The welding process was carried out on the 3-axis vertical machining center without tilt angle, using welding tools with flat or scroll shoulder surfaces. The highest tensile shear strength of 208.2 MPa using the flat shoulder was achieved under tool rotation speed of 2000 rpm and welding speed of 500 mm/min. Groove-like defects were found at the advancing side of this welding joint, which was thought to be caused by the deficiency of plastic material flow. Scroll shoulder improved the plastic material flow of aluminum alloys and weld surface without defects. However, cavities were formed in joints welding with a clearance of 0.1 mm near the interface between A6061 and SPC270. Reduction of clearance suppressed the formation of cavities and tensile shear strength of 217.9 MPa was achieved with the clearance of 0 mm. The welding interface was observed by SEM and TEM for microstructure investigation. Welding interface temperature during FSLW was measured and the factors for welding strength variation were also discussed in this paper.