Pinless FSSW of DP600/Zn/AA6061 dissimilar joints

AA6061 alloy sheets have been successfully spot-welded to dual-phase DP600 steel sheets with pinless friction stir spot welding method. The Box-Behnken design of experiments was implemented to arrange the tests. The individual and interaction effect of each process parameter on the lap-shear failure load of the joints was investigated. The maximum failure load of 4.4 kN was achieved at 1300 rpm rotational speed, 2000 kg axial force, and 10 s welding time. Microstructural features of the interfaces and phase evolution were studied by scanning electron microscope and X-ray diffraction, respectively. The bonding mechanisms at the joint interface are classified into two types: thick intermetallic layer (type I), and thin intermetallic layer with thick Zn–Al diffusion region (type II) in the aluminum/steel interface.