Refill friction stir spot welding of dissimilar metals: a review on joint behavior, simulation strategies and application challenges

As a solid-state joining process, refill friction stir spot welding (RFSSW or refill FSSW) has gained increasing importance for welding dissimilar materials due to its notable advantages over conventional fusion-based welding methods. The welding process reduces common issues such as hot (solidification) cracking as well as molten-state-related porosities while producing high-strength joints. The process is also more environmentally friendly as it does not require filler materials and produces no fumes. Despite these benefits, challenges such as increased tool wear and longer processing times still exist for dissimilar and similar welds. This review provides a comprehensive insight into RFSSW of dissimilar metals, starting with an introduction to the process and its key parameters. Following this review, an examination of the available literature highlights the influence of process parameters on weld quality, focusing on mechanical properties and corrosion behavior. This is particularly important because dissimilar material combinations exhibit differences in electrochemical potential. Additionally, recent developments in process modeling are summarized. The work concludes by addressing the potential applications of RFSSW for dissimilar structures. Finally, the work reviews key findings and offers recommendations for future research, with the aim of promoting the wider adoption of RFSSW for dissimilar material combinations and engineering structures.