Influence of heat input on pinless friction stir spot welding of aluminum‑copper dissimilar materials

The composite structures of aluminum/copper dissimilar materials hold significant practical value and potential in advanced technology and industrial applications. This study conducted lap welding experiments on 2 mm thick T2 copper and 1060 pure aluminum rods using the pinless friction stir spot welding process. By varying the dwelling time of the tool, the evolution behavior of the CuAl interface layer and the mechanical properties of the joints were analyzed. At low dwelling times, the heat input was relatively low, resulting in a thinner IMC layer and the best mechanical properties of the joints, with a pull-out force of 2238.2 N and a tensile strength of 28.49 MPa. The fracture modes of the joints under all parameters were brittle fractures. The connection of aluminum/copper dissimilar materials involves two processes: firstly, the diffusion bonding dominated by kinetics at the initial welding stage; and secondly, the solid-liquid instantaneous bonding dominated by thermodynamics. When the welding temperature exceeds the melting point of aluminum, the aluminum/copper interface continuously undergoes transformation-bonding-retransformation processes until the welding process is completed.