Dissimilar Friction Stir Welding of Austenitic and Duplex Stainless Steel: Effect of Material Position and Tool Offset

Dissimilar friction stir welding (FSW) of 2205 duplex stainless steel (2205 DSS) and 304 austenitic stainless steel (304 ASS) is carried out with various parameters. The effect of material position and tool offset on material flow and mixing, the microstructure, and the mechanical properties of joints are investigated, and the relationship between tool torque and material flow is determined. With tool offset to retreating side (RS), defect-free joints with proper material mixing are fabricated. When 304 ASS is placed on the advancing side (AS), the material mixing is better than is the case with the opposite material position, but results in a larger stirring zone (SZ) width. A large amount of mixed zone (MXZ) with a different phase ratio (gamma-alpha) from both base metals (BMs) is formed in the defect-free joints due to the alloying element diffusion between the two steels and severe plastic deformation. Due to the dynamic recrystallization, the SZ of all joints has higher hardness than 304 BM. The defect-free dissimilar joints have higher tensile strength than 304 BM and good ductility.