Effect of tool–pin offset on microstructure, mechanical properties, and corrosion behavior of friction stir welded AA2024-T3 and SS304 dissimilar joints

Abstract

The combination of aluminum and steel materials in hybrid structures shows promising applications in the automotive, marine, and aerospace sectors. The present study investigates how the tool–pin offset impacts the microstructural, mechanical, and electrochemical characteristics of friction stir-welded joints between dissimilar AA2024-T3 and SS304 materials. The optimum conditions were achieved at a tool rotation of 560 r/min, a traverse speed of 25 mm/min, and a tool–pin offset of 1 mm towards the Al side. Upon increasing the tool–pin offset to 1.5 mm, insufficient heat input resulted in inadequate plastic deformation and material flow, leading to the creation of flaws like voids, tunnels, and interfacial gaps. However, under optimal conditions, the joint exhibited a well-defined and serrated interface, with fine steel fragments securely embedded in the Al matrix. Additionally, thin intermetallic compounds were observed around the steel fragments within the Al matrix. This favorable combination resulted in enhanced tensile strength and increased ductility in the joint. The Vickers hardness test revealed that the stir zone exhibited the highest hardness values, primarily attributed to the ultra-refinement of grains. Furthermore, the potentiodynamic test revealed that the welded samples show improved corrosion resistance against the base material AA2024-T3, although BM-SS304 exhibited the highest corrosion resistance among all the samples, likely due to its higher chromium content.