Interface microstructure evolution and mechanical properties of Al/Cu bimetallic tubes fabricated by a novel friction-based welding technology

In this study, a novel friction-based welding technology was proposed for fabricating Al/Cu bimetallic tubes. The frictional heat and radial pressure during the friction-based welding process are used to achieve the metallurgical bonding between Al and Cu tubes in a rapid and efficient way. Successful joints indicate that this technology has the potential for fabricating bimetallic tubes. Microstructure evolution, bonding mechanism and mechanical properties of Al/Cu bimetallic tubes were also analyzed. Results reveal that columnar α-Al, intermediate transition layer and intermetallic compounds (IMC) are identified at the rotational speed of 950 rpm. While the rotational speed is decreased to 95 rpm, only solid-state diffusion occurs at the interface which results in three IMC layers, Al₂Cu, AlCu, and Al₂Cu₃. The thickness of the Al₂Cu is more significantly affected by the rotational speed than that of AlCu and Al₂Cu₃. Maximum hardness is observed at the reaction layer due to the formation of IMC. The appearance of intermediate transition and thick Al₂Cu layer weakens the bonding strength of bimetallic tubes. The joints are fractured at the reaction layers, and the fracture exhibits typical brittle characteristic. Three crack propagation paths are observed at the interface of Al/Cu bimetallic tubes.