Abstract:Ultrafine-grained materials generally exhibit excellent comprehensive properties but low thermal stability. The joint structure after welding is susceptible to abnormal growth, leading to a steep drop in its properties. Thus, suitable joining technology is of great engineering significance for large ultrafine-grained structural components. In this study, ultra-fine-grained copper, coarse grained aluminum, and coarse-grained copper, coarse grained aluminum was used as the structural base materials. The friction stir welding (FSW) process with low heat input was used to explore the joining. The microstructure and properties of copper aluminum joints were systematically observed. The results showed that the strong interdiffusion between ultrafine-grained copper and aluminum at the interface,resulting in the formation of more Al4Cu9 intermetallic compounds. Under a rotating speed of n=1000 r/min and welding speed of v=50 mm/min, the coarse-grained copper-aluminum joint achieved a hardness of HV 211, while the ultrafine-grained copper-aluminum welded joint demonstrated good mechanical properties.