Aluminum (Al) and copper (Cu) have been widely used in many industrial fields thanks to their good plasticity, high thermal conductivity and excellent electrical conductivity. An effective joining of dissimilar Al and Cu materials can make full use of the special characteristics of these two metals. Friction stir spot welding (FSSW), as an efficient solid-state welding method suitable for joining of dissimilar metal materials, has great prospects in future industrial applications. In this paper, the FSSW studies on Al-Cu dissimilar materials are reviewed. The research progress and current status of Al-Cu FSSW are reviewed with respect to tool features, macroscopic characteristics of welded joints, microstructures, defects in welds and mechanical properties of joints. In addition, some suggestions on further study are put forward in order to promote the development and progress of Al-Cu FSSW studies in several respects: material flow, thermal history, addition of intermediate layer, auxiliary methods and functionalization of Al-Cu FSSW joint.

The 5-mm-thick AZ61 magnesium alloy was friction stir welded by using the specially designed bobbin tool with various rotation speeds. Defect-free welds were successfully obtained with rotation speed ranging from 550 to 600 rev min⁻¹. Grain size in different regions of the joints varied depending on the rotation speed. The hardness value of the joint is uniform. The defective joint fractured in the weld nugget zone with the lowest tensile strength, while the fracture location of the defect-free joints changed to the heat affected zone. The impact energy of weld nugget zone is higher than that of the heat affected zone, and the impact energy of the two zones in defect-free joint both decreased with increasing rotation speed.

Temperature distribution and material flow behaviours during refill friction stir spot welding (RFSSW) of AZ91D magnesium alloy were studied by a combination of numerical modelling and experimentation. The coupled Eulerian–Lagrangian (CEL) formulation was adopted to analyse processing thermal history and plastic deformation mechanisms of the RFSSW joint more accurately. Welding thermal cycles of varying positions in joint were measured by thermocouples so as to validate accuracy of this simulation process. The FEA (Finite Element Analysis) simulation to cover mechanical results was found to be consistent with the experimental values. Moreover, simulation analysis presented that material flow caused the clear hook defects and bonding ligament, and such material flow behaviours were experimentally verified via the macrostructure and microstructure of the RFSSW joint.