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The butt welds of 4-mm thick 5A06 aluminum alloy plates were produced by adjustable-gap bobbin-tool friction stir travel with travel speeds of 200, 300, and 400 mm/min in this study. The microstructure was studied using optical microscopy and electron backscatter dif-fraction (EBSD). Tensile tests and microhardness measurements were performed to identify the effect of the travel speed on the joint mechan-ical properties. Sound joints were obtained at 200 mm/min while voids were present at different positions of the joints as the travel speed in-creased. The EBSD results show that the grain size, high angle grain boundaries, and density of geometrically necessary dislocations in differ-ent regions of the joint vary depending on the recovery and recrystallization behavior. Specific attention was given to the relationship between the local microstructure and mechanical properties. Microhardness measurements show that the average hardness of the stir zone (SZ) was greater than that of the base material, which was only affected slightly by the travel speed. The tensile strength of the joint decreased with in-creasing travel speed and the maximal strength efficiency reached 99%.