Microstructures and mechanical behavior of aluminum-copper lap joints

5052 aluminum alloy and pure copper (T2) are joined, using a low heat input pulsed double-electrode gas metal arc welding (DE-GMAW)-brazing method with AlSi12 filler metal. The effects of welding current (heat input) on the microstructure and mechanical behavior of the joints, which consist of Al-Al welding zone and Al-Cu brazing zone, are investigated. The Al-Cu welding zone mainly consists of alpha-Al solid solution and Al-Cu eutectic phase in coral-like shape. There exists a layer of Al2Cu intermetallic compound (IMC) in the Al-Cu brazing zone. Using the theory of thermal activation process, a quadratic relation between the thickness of the IMC layer and welding current intensity is derived. The experimental result supports this relationship. The shear strength of the Al-Cu joints first increases with the increase of the welding current (heat input), reaches a maximum of 17.66 MPa, and then decreases with the increase of the welding current due to the dispersion of the Al2Cu IMCs of large sizes in the Al alloy. Fracture of the Al-Cu lap joints occurs at three different positions, and the corresponding failure mechanisms are discussed according to the morphologies of fracture surfaces.