The Correlation of Macrostructure, Microstructure, and Texture with Room Temperature Mechanical Properties of a Twinning-Induced Plasticity Automotive Steel after Friction Stir Spot Welding/Processing

The microstructure and texture evolution of a commercialized twinning-induced plasticity automotive steel during friction stir spot welding/processing are addressed. The welding is conducted at various rotational speeds of 1000, 1600, and 2500 rpm, considering effects of strain rate and heat input on microstructural evolution. Sub grains with low angle grain boundaries are mainly developed at the thermomechanically-affected and stirred zones. At low rotational speed of 1000 rpm, continuous dynamic recrystallization occurred at the stirred zone, which eventually led to considerable grain refinement. At higher rotational speeds, dynamic recrystallization is also observed near the stirred zone. The static/dynamic microstructural evolution increased the extent of bimodality of the grain size distribution, and enhanced mechanical properties. The hook formation is hindered owning to the influence of the dynamic recrystallization on the material's flow during welding. Some fiber textures belonging to shear components are detected under low rotational speed. As deformation increased with rotational speed, shear texture further developed. Different types of shear textures of A-Fiber and B/B over bar are observed at 1600 and 2500 rpm, respectively. The mechanical properties are explored in connection with macrostructure, microstructure, and texture evolutions.