Solid state joining of stainless steel and aluminum via interlayer friction stir spot welding

Interlayer friction stir spot welding represents an advanced solid state joining technology, developed to manufacture both similar and dissimilar alloys. The incorporation of an interlayer material plays a pivotal role in preventing keyhole formation at the weld interface. This study utilizes experimental design to explore the joining of 304 stainless steel and 6061 aluminum alloy. Three key process parameters including tool rotation speed, plunge depth, and interlayer diameter are evaluated at three distinct levels. The findings indicate that the highest lap shear force of 3.66 kN can be attained by employing the optimized processing conditions. Microstructural studies reveal that the interlayer material is effectively integrated with the lower sheet, facilitated by the heat generated during the frictional process, resulting in a dendritic microstructure within the nugget zone. Moreover, fracture surface examinations demonstrate transgranular failure, providing insights on the mechanical behavior of the joints.