Recent developments in friction stir channeling: Process variants, channel morphology, and performance evaluation

Friction Stir Channeling (FSC) is an emerging solid-state manufacturing technique that enables the in-situ fabrication of continuous enclosed channels within metallic components by controlled plastic material flow. Compared with conventional channel fabrication methods such as machining, casting, and additive manufacturing, FSC offers distinct advantages including geometric flexibility, high sealing integrity, and superior energy efficiency. This review summarizes recent advances in FSC technology and its process variants—such as clearance-based FSC, large-tilt-angle FSC, rotating vortex shoulder FSC, stationary-shoulder FSC, and hybrid FSC. The evolution of tool design, channel formation mechanisms, material flow behavior, and corresponding microstructural features are comprehensively discussed. Particular attention is given to the influence of process parameters on channel morphology, surface quality, and functional performance. Notably, this article presents the first systematic summary of the impact of post-processing techniques on the thermal-hydraulic performance of FSC channels. Methods such as abrasive flow machining and electrochemical polishing are critically evaluated in terms of their effectiveness in balancing roughness reduction with hydraulic resistance. Furthermore, the mechanical, sealing, and heat transfer properties of FSC-fabricated channels are assessed. Finally, the review highlights current challenges such as tool optimization, cross-material applicability, and process stability, outlining promising research directions toward the industrial implementation of FSC-based integrated thermal management systems.