Friction stir welding of twin-roll cast EN AW 3003 plates

Abstract

Twin-roll cast EN AW 3003 plates were butt-welded with friction stir welding and their structural features were identified. Sound welds were obtained in twin-roll cast EN AW 3003 plates at tool rotation speeds higher than 500 rpm. The ultimate tensile strength of the welded plates was 134 ± 3 MPa, comparable to the ultimate tensile strength of the original plate, at 146 MPa. The stirring action of the pin fractured the interdendritic network and coarse eutectic cells, replacing the dendritic features of the base plate with a uniform dispersion of very fine intermetallic particles across the stir zone. The thermal and mechanical cycles introduced during FSW relaxed the supersaturation of the cast plate, leading to the precipitation of intermetallic particles. This precipitation activity produced a particle population gradient that peaks inside the stir zone and dictates the etching response across the plate section. The material in direct contact with the rotating pin is severely deformed and is exposed to frictional heating and inevitably undergoes dynamic recrystallization. The very fine grain structure thus obtained suffers abnormal grain growth when annealed at high temperatures due to the effective pinning of the grain boundaries by the fine particles.