The role of optimized parameters in deciding the qualities of the friction stir welded joint of 2014 aluminium alloy in terms of the mechanical properties and microstructural features was investigated in this research. A wide range of process parameters viz: tool shoulder diameter, tool pin profile, plunge depth, tool rotation speed and welding speed were selected and their individual effects on the tensile as well as microstructural properties variations were studied in detail. Out of four

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... ous selected tool pin profiles the excellent mechanical as well as microstructural properties of the square pin (SQ) tool are due to the unique stirring effect by the pulsating action of the sharp edge of the pin and metal propagation process at the stir area with incorporation with the tool rotation as well as welding speed during the friction stir welding. The SQ pin tool of 24 mm shoulder diameter with a plunge depth of 0.06 mm and tool rotating at 815 rev/mm with welding performed at a speed of 63 mm/min yielded the best quality joint. The ultimate tensile strength is around 86% of the base metal (BM) with excellent metallurgical characteristics contributed by the 84% finer grains than the BM ensured from the detail microstructural analysis of the weld bead. The metallurgical study includes the variations in the grain size at the nugget zone with respect to the selected process parameters as well. Fractography of the welded specimen reveals a ductile and transgranular mode with cup and cone structures on the counterpart.