Achieving superior strength and ductility in TWIP steel joint processed by electrically assisted friction stir welding

: The joint of twin-induced plasticity (TWIP) steel produced by friction stir welding (FSW) typically faces challenges such as inhomogeneous deformation and reduced strength and ductility. In this study, a novel electrically assisted friction stir welding (EFSW) technique was successfully employed to join TWIP steel, and the influence of EFSW on the microstructure, deformation behavior, and mechanical properties of the joint has been systematically investigated. The results showed that, the grain size in the stir zone (SZ) of EFSW joints was significantly refined (from 3.81 μm of FSW joint to 1.79 μm EFSW joint), and dynamic recrystallization was promoted, with its proportion increasing from 15.9% to 30.6%. The grain size in the heat affected zone (HAZ) coarsened, and the content of annealing twin boundaries increased to 30.5%. During tensile deformation, a gradient deformation from the base metal (BM) to the HAZ and then to the SZ was exhibited in the EFSW joint, which significantly improved the deformation uniformity. The fracture location shifted from the SZ in the FSW joint to the BM in the EFSW joint. The EFSW joint exhibited high strength and ductility, and ultimate tensile strength and elongation were 1045 MPa and 66.2%, respectively. The product of strength and elongation reached 69179 MPa·%, corresponding to 103% of that of the BM and significantly surpassing that of the conventional FSW joint. This provides a novel welding strategy for high-quality preparation of TWIP steel joints.