Subgrain formation in ultrasonic enhanced friction stir welding of aluminium alloy
Abstract Recrystallization fractions in the stirred zone of Al 6061 T6 friction stir welds, prepared with and without ultrasonic vibrations, were evaluated using recrystallization fraction maps. Based on the maps, it was suggested that the microstructure evolution can be described as different dislocation manipulation processes. It was observed that superposition of static load of FSW on residual ultrasonic softening induces subgrain formation. Subgrain formation was substantial at the center of the stirred zone where the ultrasonic impact was the maximum.