Recent developments and current status of keyhole TIG welding: A comprehensive review

Gas tungsten arc welding is a widely used metal joining process across manufacturing industries due to its ability to produce high- quality welds with excellent precision and cleanliness. However, gas tungsten arc welding is limited by relatively low welding speeds, reduced filler material deposition rates, and shallow penetration, which constrain its efficiency for medium and thick section fabrication. Keyhole tungsten inert gas welding extends the capabilities of conventional gas tungsten arc welding by enabling stable, single-pass, full-penetration welding in medium to thick section materials. Although welding speeds in true keyhole mode are governed by weld pool stability, overall productivity and weld quality are improved through the elimination of complex edge preparation and multi-pass welding. Compared to high-power-density processes such as plasma arc welding, laser beam welding, and electron beam welding, keyhole tungsten inert gas welding provides a cost-effective and operationally simpler alternative for medium to thick section fabrication. This review examines the current research status and technological progress of keyhole tungsten inert gas welding, classifying and summarizing the process based on microstructural evolution, artificial intelligence-based process monitoring, multiphysics numerical modeling, and emerging technology variants. By comprehensively analyzing the process characteristics and underlying mechanisms, the novelty of this work lies in integrating these aspects into a unified framework, thereby strengthening the knowledge base of keyhole tungsten inert gas welding and providing clear direction for future research. Furthermore, this review offers a valuable reference for researchers and industry practitioners seeking to advance high-productivity welding technologies.