FEM Analysis and Verification of Pinless Friction Stir Spot Welding of Cu and Al with Zn Interlayer: Effect of Shoulder Diameter and Spot Pass

Abstract

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.