Effect of process parameters on interfacial microstructure and mechanical properties of Al/Cu friction stir lap welding joints

In this study, friction stir lap welding (FSLW) was performed for the welding test of 6061 aluminium alloy and T2 pure copper. The effect of process parameters containing rotation rate and travel speed on interfacial microstructure evolution and mechanical properties of Al/Cu dissimilar joints were explored. The experiments were carried out under the rotation rates of 600, 900 and 1200 r/min and with the travel speeds of 30, 70 and 100 mm/min. The characteristic of interface transition zones (ITZs) and the species of intermetallic compounds (IMCs) were investigated. The Al/Cu interface showed a layered structure composed of Al-Cu IMCs, which will affect the mechanical property. The layer consisting of Al₂Cu was formed at lower heat input, and as heat input increased the Al₄Cu₉ phase started to form. Excessive heat input will increase the thickness of the interface and raise the brittleness of the joints. The thickness of the IMCs layers changed from 0.89 μm to 3.96 μm as the heat input increased. The maximum value of tensile shear loading of 4.65 kN was obtained at the rotation rate of 900 r/min and travel speed of 100 mm/min with the interface thickness of 2.89 μm. The fracture mode of the joints was a mix of ductile and brittle fracture.