Abstract: This paper presents ultrasonic welding tests conducted separately on tin-plated and bare copper wires. It examines the temperature at their welding joints and analyzes joint performance under various welding energies. The study explores the influence of the tin coating on the joint performance of copper wires. The results demonstrate that ultrasonic welding effectively connects tin-plated copper wires. The welding strength of both types increases gradually with higher welding energy. Due to the low melting point of the tin coating, it melts and fills the interface during ultrasonic softening, isolating atomic diffusion and penetration. This results in a significantly lower strength of tin-plated copper wires compared to bare copper wires across different energy levels. As welding energy increases, the temperature at the welding interface rises, causing the tin coating to melt, which allows for the formation of a metallurgical bond between the tin-plated and bare copper wires, leading to a marked increase in strength. The fracture surface of the joint displays clear ductile dents, indicating a ductile fracture mode and strong joint performance.