• EFSW refined the stir zone grain size from 3.67 μm to 1.39 μm, while the heat-affected zone coarsened to 4.19 μm.
• The EFSW joint achieved 1055 MPa ultimate tensile strength (103.3% of BM) and 561 MPa yield strength (111.1% of BM), with 60.8% elongation (92.4% of BM).
• Plastic deformation concentrated in the base material, with notable deformation in both SZ and HAZ, and fracture occurred in the BM, indicating superior weld integrity.
• EFSW is a promising solid-state welding technique for TWIP steel, mitigating fusion-welding defects while enhancing strength.