Water-temperature-controlled process optimization for enhanced interfacial bonding in Al/CFRP FSLW

With the rapid development of transportation and aerospace industries, the increasing emphasis on lightweighting has created a demand for advanced metal/polymer joining technologies. Underwater welding is an optimization way to reduce excessive heat effects of joints and improve welding efficiency. To mitigate the overflow of molten polymer matrix during the welding process of carbon fiber reinforced thermoplastic (CFRP) and aluminum alloy, process optimization experiments of water medium-assisted CFRP/aluminum alloy friction stir lap welding (FSLW) are carried out. For this purpose, a welding tool with water circulation function is designed and developed. The influences of water medium on material interface behavior, flow characteristics, and defect control are analyzed. By observing the joint boundary thickness and the interweaving combination of dissimilar materials under different water temperatures, the regulatory effects of water temperature on the microstructure and mechanical properties of the joint are studied. As the water temperature increases, the aluminum alloy is embedded into the CFRP in a plastically deformed state, and the thickness of the aluminum alloy at the joint bottom gradually increases, which enhances the load-bearing capacity of the dissimilar joint. The lap shear strength of the joint reaches 43.3 MPa at the 80°C water temperature.