EFFECT OF FRICTION-STIR-WELDING PARAMETERS ON THE WELDING MICROSTRUCTURE AND PROPERTIES OF 5083 AND 7075 ALUMINUM ALLOYS

In the friction stir welding (FSW) of 5083 aluminum alloy, an increased tool rotation speed at a constant welding speed promotes flash defects but enhances the symmetry of the "basin-like" weld morphology. The nugget zone features dynamically recrystallized equiaxed grains with peak hardness at the weld center (sharply rising under abrupt rotation acceleration), while the thermo-mechanically affected zone (TMAZ) displays a plastic-deformation microstructure. For 7075 aluminum alloy joints, the grain sizes follow TMAZ > base material > nugget zone, where higher rotation speeds coarsen the nugget/TMAZ grains, whereas increased welding speeds refine them. The average weld hardness reaches 86.6 HB, exceeding TMAZ values, with abrupt rotation speed changes triggering significant hardness surges in 5083 welds.