Abstract
Tensile strength, porosity and microstructure evolution of ultrasonic bonding for BVR2.5 Cu cables at different welding energies were investigated. By X-ray computed tomography and modification of the Johnson-Cook model, the predictive model of porosity was developed for the first time to assess joint strength. When the porosity was lower than 19%, the joint formed a good bond and reached the tensile strength of 585.7 ± 17.9 N. The maximum joint tensile strength was achieved at about 10% porosity. The Cu grains at the interface underwent plastic deformation, discontinuous dynamic recrystallisation and dynamic recovery to form a good bond. Interfacial grains are refined by ultrasonic vibrations, but the reduction of the porosity is the critical factor in improving joint strength.
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