No abstract

In this study, the pinless friction stir spot welding of aluminum–copper composite with Zn interlayer was analyzed under experimental measurement and finite element method. The role of shoulder diameter, 16, 18, and 20 mm, and the number of spot pass, one to three pass, on microstructure, mechanical properties, and thermal history of weld samples were investigated. Based on the obtained results, there is a good agreement between numerical data and experimental analyses. It was shown that the heat source, due to plastic deformation and friction, increased as the shoulder diameter was increased, whereas the stress distribution in the weld samples was reduced. In addition, the thickness of the Zn interlayer at the joint interface changes when shoulder size increases from 16 to 20 mm, due to high temperature and intermixing between materials. From the microstructure analysis, the grain size in the joint zone gradually decreases as the spot pass increases from 1 to 3. It was concluded that the shoulder diameter of 16 mm with three spot passes showed the best result of 7.45 kN. Depending on X-ray diffraction analyses of the fracture surfaces, three primarily intermetallic phases including the Al2Cu, CuZn5, and CuZn2 were determined in the weld interfaces. Based on finite element method analysis, the axial compressive stresses showed the lowest profile as the shoulder diameter of the tool is 16 mm. Finally, the ductile fracture was detected as the main fracture mechanism for the joint sample with optimal joining conditions.

A three-dimensional model for the pinless friction stir spot welding (P-FSSW) of copper-aluminum alloy with zinc interlayer was developed by the ABAQUS/Explicit. The distribution of temperature and stress at the joint zone, at three different shoulder diameters (including 16, 18, and 20 mm) and spot pass-number (including 1 to 3 pass), were simulated and verified by experimental measurements. Microstructural characteristics of the joint interfaces and phase evolution were analyzed by scanning electron microscope and X-ray diffraction, respectively. The numerical and experimental results showed a good agreement and it was found that with increasing shoulder diameter, heat generation by friction and plastic deformation was improved, while the stress was decreased. Mechanical measurements indicated that the best result of 7.45 kN was achieved for a shoulder diameter of 16 mm and three spot pass. From XRD analyses of the fracture surfaces, the Al2Cu, CuZn5, and CuZn2 intermetallic phases were detected in the joint interfaces. The simulation results showed that the axial compressive stresses experience the lowest values when the shoulder diameter is 16 mm. The fracture surface analysis showed the ductile fracture for weld sample joined under optimal welding condition namely shoulder diameter of 16 mm after three spot pass.