Role of Pin Profile and Offset in Interfacial Characterization and Mechanical Behavior of Dissimilar Friction Stir Welded T-Lap Joints

This study investigates the role of pin profile in the interfacial characterization of friction stir welded (FSWed) T-lap joints fabricated with dissimilar aluminum alloys (AA5083 and AA7075) under regimes of two welding passes. Various pin offset distances and three pin profiles (cylindrical non-threaded, cylindrical threaded, and triangular pins) were examined with the results indicating that the pin profile significantly affected the interfacial morphology and formation of kissing bonds (KBs). Threaded pin produced a higher and wider mixing zone but resulted in larger KBs. The cylindrical non-threaded and triangular pins minimized the size of KBs but exhibited weaker material mixing. The pin offset had minimal effect on the interface morphology but reduced the size of KBs remarkably with increasing distance offset. The mechanical performance of the T-lap joints was evaluated through tensile tests, hardness distribution, and local strain using digital image correlation analysis. Increasing the pin offset improved joint strength, particularly in the stringer test. The cylindrical non-threaded pin achieved the highest joint efficiency (90 pct compared to the base material) owing to its optimal balance between effective bonding width and effective skin thickness. KBs were identified as the weakest point in the FSWed T-lap joint, causing localized strain and influencing the fracture behavior.