Novel approach to refill probe hole in friction stir spot welding of AA 6061-T6 sheets

Abstract

Friction stir spot welding (FSSW) is a solid state welding process suitable for light weight materials in applications such as automobile bodies and chassis assemblies which are difficult to weld with conventional spot welding processes. It is a derivative of friction stir welding where only the tool is plunged into the material and retracted, resulting in a spot weld. FSSW has proven to be a better alternative over the resistance spot welding to weld these materials due to improved mechanical properties, energy efficiency and reduction in operating costs. But probe hole left behind is the main problem in conventional FSSW. In the present study an attempt is made to develop novel approach to refill probe hole using an additional plate called filler plate. This new refilling technique and conventional FSSW process were used to weld AA 6061-T6 sheets and the results were compared. Effect of tool rotational speeds on mechanical and metallurgical properties in both the cases were studied. Static shear strength of refilled weld samples was found to be better than the conventional FSSW process at all tool rotational speeds. The hardness profile of the welds exhibited a W-shaped appearance in all the processes and minimum hardness was measured in the heat affected zone (HAZ). Modes of fracture were studied and analysed through scanning electron microscope (SEM).