Industries are increasingly pursuing sustainable solutions, leading to the adoption of lightweight materials like aluminum and magnesium in aerospace and automotive sectors. The joining of these dissimilar materials allows for multi-material structures that harness their advantageous properties. However, excessive intermetallic compound formation at the joint interface can compromise mechanical integrity. Solid-state joining techniques present a viable solution, as they function at lower temperatures, limiting the thickness of intermetallic compounds. This study utilizes numerical techniques, specifically finite-element and multiphase-field methods, to investigate intermetallic compound evolution during solid-state joining processes. The finite-element method simulates the refill friction stir spot welding process for aluminum and magnesium, while the multiphase-field method examines intermetallic compound development at the joint interface. The simulation yields a temperature and strain profile that influences intermetallic compound evolution. The multiphase-field model further analyzes the morphology and kinetics of these compounds under various driving forces, including chemical and mechanical effects. Key parameters such as interface energy, grain boundary diffusion, and initial microstructure are explored, revealing their significant impact on the final morphology and kinetics of intermetallic compounds. This combined num
