Ultrafine-Grained Microstructure and Improved Mechanical Behaviors of Friction Stir Welded Cu and Cu–30Zn Joints

Ultra-strong joints of pure Cu and Cu–30Zn alloy were obtained by friction stir welding under flowing water. The effects of heat inputting condition and material characteristics on the morphologies, microstructures and mechanical properties of welding joints were studied. Defect-free stirring zones of pure Cu and Cu–30Zn were characterized by onion-ringed structure and plastic flowing bands, respectively. Both low stacking fault energy and fast cooling condition contributed to the formation of small recrystallized grains less than 1 μm in stirring zones. The welding joints in both materials exhibited enhanced mechanical performances due to ultrafine-grained microstructure in stirring zones and disappearance of soft heat-affected-zone. The technique of digital image correlation was used to study the tensile deformation behaviors of welding joints and verify the improved tensile properties.