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Impact of tool profile on mechanical behavior and material flow in friction stir welding of dissimilar aluminum alloys

The tool pin geometry used in friction stir welding of any material affects the transportation and mixing of the materials at the joint interface during the welding process. This further affects the mechanical properties of the joint. Tapered threaded and unthreaded tool pin profiles were investigated in this research work. The relationship between the material mixing characteristics and mechanical properties of each pin profile were evaluated. The results indicate that more materials mixing occurred in the nugget zone of the welds at lower rotational speed with the threaded tool pin than the unthreaded tool pin. However, at medium rotational speed, more volume of materials was swept into each other better in the unthreaded tool pin than the threaded pin. The tensile strengths of welds with the threaded tool pin were higher than the unthreaded tool pin. Although the two tool pins exhibit similarities in hardness variations across the weld zones however, higher average values of hardness were obtained at the nugget zone for welds performed with the tapered threaded tool pin. These could be as a result of better material mixing and higher opposition to grain dislocations across the dividing lines in the welds from the threaded tool pin.