Study on the new friction stir spot weld joint reinforcement technique on 5754 aluminum alloy

In this study, new friction stir spot welding method was developed using two different tools in order to create a spot weld without keyhole. The effects of process parameters and tool geometry were considered to improve the weld joint properties. The shear-tensile tests and microstructure study showed that the new method could offer superior performance in comparison to conventional friction stir spot welding. By controlling the process parameters, spot welds with strength about 37% higher than the conventional friction stir spot welds were obtained. The stir zone grain size of the prepared samples in the optimum welding conditions was decreased about four times than the base metal. It was observed that the tool plunge depth in both welding and refilling steps play a key role in creating a sound high strength welded joint. The failure load of the spot welds manufactured by concave shoulder was found to be about 7% higher than the failure load of the prepared spot welds by the flat shoulder