Microstructural modification and stress corrosion mechanisms of in-situ rolling friction stir welding joints

In-situ rolling friction stir welding (IRFSW) was utilized to modify surficial stress state along with welding process synchronously, integrating welding and surface modification into a single step. Transformation of surficial residual stress was triggered from 100 ± 7 MPa to −30 ± 6 MPa, attributed to severe plastic deformation during in-situ rolling. Meanwhile, IRFSW induced fragmentation and homogeneous re-dispersion of intragranular precipitates, narrowed and even eliminated grain boundary precipitation-free zones (PFZ), and transformed grain boundary precipitates (GBPs) from continuous to discontinuous distribution. These combined effects effectively inhibited micro-galvanic corrosion and blocked intergranular corrosion paths. The stress corrosion depth and corrosion current density of the IRFSW joint were decreased by 43.7 % and 76.7 % compared with those of the conventional joint under high tensile stress. A density functional theory model was developed to qualitatively illustrate that compressive stress reduces the anodic dissolution rate by elevating the work function and decreasing the surface energy density, thereby providing theoretical support for the enhanced stress corrosion resistance of the IRFSW joint.