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Microstructural features and mechanical properties of friction stir welded (FSW) EN AW 5083 H111 plates were investigated. Friction stir welding led to the fragmentation of coarse Al6(Mn,Fe) particles, the dissolutionising of fine Al3Mg2 particles and to recrystallisation across the nugget zone (NZ), producing hardness profiles that show little or no variation across the joint. The joints produced at a welding speed of 80 mm/min were larger than those produced at 125 mm/min. The shape of the joint, on the other hand, was dictated by the pin profile. Joints produced by the threaded circular pin invariably revealed elliptical NZs while the NZs of the joints produced by the triangular pin were basin-shaped. The welding speed also had an impact on the NZ grain size and the tensile properties of the joint. The NZ grain size was smaller, the ultimate tensile strength (UTS) and the elongation values were higher at a welding speed of 80 mm/min than at 125 mm/min for both pin profiles. The superior tensile properties at the lower welding speed were consistent with the smaller grain size and bigger joints in the former. The joint efficiency of the EN AW 5083 plates welded with a triangular pin at a tool rotation rate and welding speed of 800 rpm and 80 mm/min, respectively, was estimated to be as high as 97.

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This article presents an approach related to the dissimilar friction stir welding of AA6082 and AA7075. The effects of tool type, tool rotational speed and welding speed on the ultimate tensile strength (UTS) and percentage of elongation were investigated using grey relational analysis and then the optimal combination was determined. The results of a series of analyses revealed that the tool type 4, a tool rotational speed of 1000 rpm/min and a welding speed of 100 mm/min correspond to the optimal condition. Except for tool rotational speed, the other factors are significant at 95% and affect the grey relational grade value with a percentage contribution sorted in descending order as welding speed (48.7%), tool type (27.48%) and tool rotational speed (15.13%). A confirmation experiment was carried out to verify the optimised parameters. The result indicated that an improvement was achieved in ultimate tensile strength and percentage of elongation.

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