Abstract: 12 mm medium-thick AA6061-T6 aluminium alloy and T2 pure copper was welded by double-sided stir friction welding, the influence of welding parameters on the microstructure and mechanical properties of the joint was investigated. It was found that there are significant differences in the weld formation between the first-pass and second-pass welds at both sides due to welding distortion even through the same welding parameters were used for those two welds at both sides, making it difficult to achieve excellent joint properties. In order to further improve the joint properties, the rotational speed and welding speed of the first-pass weld were fixed at 600 r/min and 400 mm/min respectively, while the welding parameters of the second-pass weld were investigated and optimized. On one hand, the rotational speed of the second-pass weld was fixed at 600 r/min while change the welding speed to 300 mm/min, 200 mm/min and 100 mm/min, respectively. A defect-free joint is achieved at the welding speed of 100 mm/min for the second-pass weld. On the other hand, the welding speed of the second-pass weld was fixed at 400 mm/min while change the rotational speed to 800 r/min and 1 000 r/min, respectively. The results showed that the defect-free joint with a maximum tensile strength of 151 MPa was obtained at the tool rotation speed of 800 r/min for the second-pass weld. This is because there isn’t any cavity defects and micro-cracks at the aluminium/copper interface, as well as the relatively thin intermetallic compound layer was formed at the Al/Cu interface under the optimized condition. The joint was fractured at the aluminium/copper interface and the fracture mode was classified as a ductile-brittle mixed fracture.

Key words: aluminum/copper dissimilar welding, double-side friction stir welding, medium-thick plate, interface intermetalic compounds, mechanical properties