Effect of thickness variation on ultrasonic welding of aluminum-copper joints

Al shares similar properties with Cu and is abundant, lightweight and cost-effective. As a result, replacing Cu with Al has become a key focus in scientific research and engineering applications. This paper examines the effect of different thickness combinations of Cu and Al plates on the quality of ultrasonic welding (USW), temperature distribution, joint mechanical properties and failure modes under consistent welding parameters. The peak temperature at edge is 125.4°C for a 2 mm Al plate, 135.4°C for a 2.5 mm Al plate and 120.1°C for a 3 mm Al plate. EDS analysis indicates the largest diffusion width in Cu1.5-Al2.5 joint section, measuring approximately 4.98 μm. Cu1-Al3 joint has smallest diffusion width at 1.62 μm. The Cu1.5-Al2.5 joint exhibits highest strength with an average tensile force of 5612.00 N, followed by Cu2-Al2 joint with second-highest strength. Cu1-Al3 joint displays the lowest strength. Regarding electrical resistance, the resistance of Cu2-Al2 and Cu1.5-Al2.5 joints remains nearly unchanged while the Cu1-Al3 joint displays highest resistance. The fracture morphology of Cu1.5-Al2.5 and Cu2-Al2 joints shows a significantly larger fractured area compared to flat zone with a considerable amount of Al residue observed at fracture edge on Cu side.