Friction stir spot welding (FSSW) is one of the solid state welding methods and dissimilar material joining by FSSW has been investigated. “Scrubbing refill FSSW (Sc-RFSSW)” has developed as a new dissimilar material joining method, and it was shown that Sc-RFSSW provides higher joint strength than conventional FSSW methods in joining the aluminum alloy and non-coated steel. In this study, the microscale testing was performed to evaluate the dissimilar material interfacial strength of Sc-RFSSW joints. The relationship between the interfacial strength distribution and the macroscopic strength of the Sc-RFSSW joint was analyzed. In addition, the microstructure of the dissimilar material interface was observed, and the relationship between the microstructure and the interface strength was shown.
