Recent progress and perspectives in fusion welding of Mg-RE alloys: From weldability fundamentals to process-microstructure correlation

Magnesium-rare earth (Mg-RE) alloys are pivotal for lightweight applications in aerospace and advanced engineering due to their high specific strength. However, manufacturing large-scale complex components via monolithic casting is challenging owing to defects such as RE oxides and shrinkage porosity, making fusion welding essential for both defect repair and structural joining. This review comprehensively examines recent advances in fusion welding of Mg-RE alloys, with emphasis on the interplay between their unique physicochemical properties and welding metallurgy. Various fusion welding methods suitable for Mg-RE alloys are compared and analyzed. Detailed characterization of joint regions reveals how thermal gradients and cooling rates govern phase evolution, grain morphology, and defect formation. Moreover, welding parameters and heat treatment strategies are systematically discussed for the microstructural configuration, especially for the inherent conflicts between grain coarsening in fusion zone and eutectic dissolution in heat-affected zone. Future research directions are also outlined. By correlating Mg-RE alloy properties with fusion welding processes, this review provides practical insights for designing reliable welded structures in critical applications.