<i>In-situ</i> rolling friction stir welding enables co-controlled weld distortion and thinning

Weld distortion and thinning critically affect the quality of friction stir welded (FSW) thin-walled sheets. Here, in-situ rolling FSW (IRFSW) was proposed to join 7075-T6 sheets with co-controlling distortion and weld thinning. The novel IRFSW tool was composed of inner and outer double-shoulders and circumferential rolling balls. The double-shoulder structure suppresses material overflow and the rolling balls regulate surface residual stress. The IRFSW process produced defect-free joints with minimal thinning (0.03 mm), whose surface finish was improved by 80.7%, and the longitudinal and transverse distortions of the IRFSW joint were reduced by 83.7% and 62.1% compared with those of the conventional joints. The ultimate tensile strength of the IRFSW joint reached 483 ± 2 MPa, retaining 86.1% of the base material's tensile strength. This study will provide powerful technical strategy and theoretical support for achieving low distortion and micro-thinning friction stir welding of thin sheets.