Comparative study on microstructure characteristics and mechanical properties of dissimilar friction stir welded aluminum alloy using single and double rotating shoulder tools

This study investigates the friction stir butt of 2024 aluminum alloy with 6061-T6 aluminum alloy using both double rotating shoulder friction stir welding (double rotating shoulder friction stir welding, DRS-FSW) and conventional friction stir welding (FSW) techniques. The differences in joint structure and morphology and mechanical properties between DRS-FSW and FSW joints were investigated. Defect-free joints were obtained for both DRS-FSW and FSW at a rotational speed of 600 r/min and a welding speed of 30 mm/min. Compared to the cross-section morphology of the dissimilar aluminum alloy joints of FSW, the morphology of the shoulder-affected zone (SAZ) and weld nugget zone (WNZ) of the DRS-FSW joints is more complex. The longitudinal morphology of the DRS-FSW joints shows complex material flow variations. The microstructure of the weld nugget zone (WNZ) of DRS-FSW joints is dominated by recrystallization. The microhardness magnitude and distribution are approximately the same for both. The FSW tensile properties are higher than those of DRS-FSW. Both DRS-FSW and FSW tensile fracture locations are in the heat-affected zone (HAZ) on the retreating side (RS) of the joint, and both exhibit ductile behavior. This paper is a further exploratory study of the double stirring technique.