Forming Quality and Failure Behaviors of Al/Cu Ultrasonic Welding Joints with Additional Ni, Zn, and Mg Interlayers

The presence of intermetallic compounds (IMCs) can significantly reduce joint mechanical properties, leading to premature failure. In this paper, mechanical manufacture and forming quality analysis of ultrasonically welded (Al/Cu) joints is proposed and investigated by adding different thicknesses interlayers (e.g., Ni, Zn and Mg). The peak load of the joint first increases and then decreases as the Ni interlayer thickness rises. The plastic yield of the 0.10 mm thick Ni interlayer is poor after its failure, leading to an advantageous wavy interface. Three interface bonding modes, e.g., Al- Ni, Cu- Ni and Al-Cu, are better than Zn joints in tensile strength and impact resistance. When the thickness of Ni interlayer is greater than 0.05 mm, the interlayer will not tear during shear tensile. The failure mode of the Cu side is ductile fracture, and the Al side is mixed ductile and brittle fracture. Investigation indicates that the thickness of interlayers significantly affects the formation quality of microstructure. The Ni interlayer with a thickness of 0.1 mm produces the best wavy interface and reduces IMCs under optimized parameters such as P = 0.3 MPa, Amp = 50% and W.E = 2500 J. Ni interlayer promotes the formation of a uniform IMCs layer at the interface between Al and Cu sheets, which contributes to improvements in the mechanical properties of welded joint. In addition, it produces effective deformation in interface microstructure, reducing oxide layers and corrosion effect.