Microstructure, mechanical properties and deformation behavior of electrically assisted friction stir welded TWIP steel joint

In this work, twin-induced plasticity steel was processed by electrically assisted friction stir welded (EFSW). The microstructure, mechanical properties, and deformation behavior of the joint were investigated. The results show that the average grain size was refined from 3.67 μm in base material (BM) to 1.39 μm of stir zone (SZ), while that increased to 4.19 μm of heat affected zone (HAZ). The fraction of twin boundaries (TBs) decreased from 20.7% in the BM to 6.91% in the SZ, but increased to 24.5% in the HAZ. The ultimate tensile strength, yield strength, and elongation of the BM were 1021 MPa, 505 MPa, and 65.8%, respectively. For the EFSW joint, the ultimate tensile strength, yield strength, and elongation were 1055 MPa, 561 MPa, and 60.8%, which reached 103.3%, 111.1%, and 92.4% of the BM, respectively. During the tensile test, the plastic deformation of the joint was predominantly concentrated in the BM, while the SZ and HAZ exhibited significant plastic deformation, and the fracture occurred in the BM.