Microstructure and properties of aluminum/copper blue-red hybrid laser welded joint

In order to realize efficient and reliable welding of power battery, 1050 aluminum/T2 copper lap welding was carried out by using blue-red laser heat source. The effects of laser power on the microstructure, phase distribution mechanical properties and electrical conductivity of the joint were investigated. The results show that the weld surface of Al/Cu lap joint is smooth and the section is “T” shape. When PB (Blue laser power) remains 300 W, PR(Infrared laser power) increases in 700 W ~ 1400 W, the copper side penetration depth increases from 60 μm to 1000 μm, achieving a good metallurgical bonding with P_R = 800 W. The weld microstructure is composed of Al solid solution, Al-Cu eutectic alloy and Al₂Cu intermetallic compound phases. With the increase of laser power, Al₄Cu₉ phases appear locally in the weld, and AlCu, Al₄Cu₉ and AlCu₃ phases appear at the edge. When P_R = 800 W, the weld strength reaches the maximum of 108.6 MPa, and the contact resistance reaches the minimum of 94 μΩ. The crack starts from the junction of two plates region (Al₂Cu) and extends along the weld edge from the outer Al₂Cu region to the junction of Al solid solution and Al-Cu eutectic alloy at the bottom. The fracture form is cleavage fracture.