Investigations into the formation of intermetallic compounds during pinless friction stir spot welding of AA2024-Zn-pure copper dissimilar joints

In the current study, the pinless friction stir spot welding (P-FSSW) method was applied for joining dissimilar AA2024-pure copper alloys. The present article focuses on the role played by a zinc foil interlayer with different rotational speeds and welding time in developing microstructure and mechanical properties of aluminum-copper pinless friction stir spot welds (P-FSSW). The formation and type of intermetallic compounds (IMCs) were deeply analyzed during the P-FSSW process. Microstructural characteristics of the interfaces and phase evolution were examined by optical microscope and scanning electron microscope equipped with energy-dispersive spectroscopy, respectively. It was shown that increasing the rotational speed and dwell time leads to increased heat input during the P-FSSW process, affecting intermetallic compounds’ (IMCs’) growth. It was concluded that the formation of brittle Al2Cu is the main IMCs phase in the joint surface. The result indicated the maximum failure load of 7.24 kN with the acceptable IMCs thickness of 27.21 μm is obtained at 2000 rpm rotational speed and 5-s dwell time. Furthermore, the highest hardness is located at the center area of the joints. The fracture surface analysis indicated the ductile fracture for the weld sample produced by the rotational speed of 2000 rpm and welding time of 5 s.