Laser micro-welding technology for Cu–Al dissimilar metals and mechanisms of weld defect formation

Abstract

To study laser micro-welding technology for copper–aluminum (Cu–Al) dissimilar metals and the intrinsic mechanisms of weld defect formation, we used a 300-W energy negative-feedback Nd:YAG pulsed laser welding system for laser micro-welding of two dissimilar metals, i.e., a Φ0.25-mm thin Cu wire and an Al pin. The former has a high melting point and good fluidity, whereas the latter has poor fluidity, is hard to weld, is easily oxidizable, and easily forms weld defects such as blowholes. Under laser irradiation, the Cu metal was melted to coat the Al material, which then melts, followed by solution-diffusion to accomplish the welding. We selected a laser beam with a rapid ascending and slow descending waveform, a pulse width of 3.0 ms, a peak power of 0.7 kW, and a single pulse energy of 3.3 J to enable successful welding at a negative defocus of −0.5 mm. Finally, the microscopic mechanisms of weld formation during laser micro-welding of Cu–Al dissimilar metals were analyzed; the causes of the formation of hot cracks and blowholes were analyzed in detail from aspects of Cu–Al dissimilar metals such as physical properties, lattice structure, and latent heats of solidification, and accordingly, solutions are proposed to provide a reliable theoretical basis for laser welding of Cu–Al dissimilar metals.