Friction Stir Processing: An Eco-Efficient Route to High-Performance Surface Architectures in MMCs

Friction Stir Processing (FSP) has emerged as an advanced solid-state surface engineering technique for tailoring high-performance surface architectures in metal matrix composites (MMCs). By combining localized thermo-mechanical deformation with controlled material flow, FSP enables grain refinement, homogeneous dispersion of reinforcement, and strong interfacial bonding without melting or altering bulk properties. This review critically examines the role of FSP in enhancing the mechanical, tribological, and corrosion performance of composites, with emphasis on process–structure–property relationships. Key strengthening mechanisms, including grain boundary strengthening, load transfer, particle pinning, and defect elimination, are systematically discussed, along with their implications for wear resistance, fatigue life, and durability. Special attention is given to corrosion and tribo-corrosion behavior, highlighting electrochemical mechanisms such as micro-galvanic interactions, passive film stability, and interfacial chemistry. Furthermore, the eco-efficiency, industrial viability, and sustainability advantages of FSP are evaluated in comparison with conventional surface modification techniques. The review concludes by identifying critical challenges and outlining future research directions for the scalable, multifunctional, and sustainable design of composite surfaces.