Enhancing Microstructural, Textural, and Mechanical Properties of Al–Ti Dissimilar Joints via Static Shoulder Friction Stir Welding

The present study explores the application of static shoulder friction stir welding (SSFSW) to address the challenges of poor mechanical properties in conventional Al–Ti dissimilar friction stir joints, which arise due to significant material mixing, and the formation of thick intermetallic layers. The results show that SSFSW inhibited material mixing, and the mutual diffusion of Al and Ti was suppressed due to lower heat input. Mutual interdiffusion of Al and Ti was directed by an exothermic chemical reaction, forming an Al₅Ti₂—Al₃Ti sequence due to the sluggish diffusion of Al in Ti at a temperature of 512 °C achieved in this study. The microstructure at the stir zone (SZ) comprised equiaxed grains with Ti particles acting as dispersoids for nucleation, whereas the presence of large Ti blocks at SZ of conventional FSW (CFSW) resisted plastic deformation, resulting in a nonhomogeneous concentration of dislocations near its interface. A significant decrease in grain size at all the critical zones of weldment was due to the rearrangement of dislocations through the slip-and-climb mechanism, as evidenced by the occurrence of dynamic recrystallization. The emergence of γ-fiber and basal fiber texture contributed to a significant enhancement in the tensile strength of SSFSW (289 MPa). The study also analyzed the various strengthening mechanisms contributing to the improved yield strength of SSFSW weldments, and the results showed that grain boundary strengthening plays a predominant role in enhancing the strength of SSFSW.