Friction Stir Welding of Dissimilar Butt Joints with Novel Joint Geometry

In this study, 1 mm thin sheets of AA 6061 and steel were welded by friction stir, with new joint geometry. Conventional friction stir welding develops high distortion to the specimen, particularly when the thickness is very small. In this process, friction stir welding is carried out by a tool without probe and with new joint geometry. Contrary to the conventional friction stir welding, where various tool profiles are used to obtain successful joints, the present study of investigation focused on developing a profile in the sheet metal edges to be joined. The aluminium sheet was positioned on the contoured steel sheet. Rotating tool with tilt angle was made to progress into the top sheet. Frictional heat plasticized the upper blank and the edges of the aluminium sheet were forged and extruded into the steel contour. The welding between steel and aluminium was due to a coalescence of the two materials and clamping effect was provided by the contour in the steel sheet. Tensile test was conducted to evaluate the quality of the welding along with macro and micro metallographic investigations. Further to this, scanning electron microscopy with energy dispersive X-ray and X-ray diffraction analysis have been done to understand the presence of intermetallics at the weld nugget. Tensile strength of 122.22 MPa was achieved. Intermetallics of Mg₂Si, MnAl₆ and FeAl₆, Al₅Fe₂ was found as dominant compound at the interface. Welding of thin sheets is enhanced by form clamping and chemical diffusion bonding.