Abstract: In order to investigate the effect of preheating on the laser lap welding, Nd:YAG laser and aluminum alloy 5A03H24 plate of 1.4 mm thick are used to carry out experiments of laser lap welding without preheating and with preheating at 300 ℃ respectively. The results indicate that preheating can accelerate welding speed greatly while the penetration depth and width, heat affected zone width and tensile shear strength are basically unchanged. Compared with laser welding without preheating, Mg element concentration in weld is almost the same during high speed welding with preheating. The tensile fracture microstructures are all micro-void coalescence type plastic fractures. The weld structures are all composed of columnar dendrites and equiaxial dendrites, and the columnar dendrites near fusion line are similar in structure. However, the hardness of weld and base metal is decreased, and the former decreases more in hardness than the latter.

Key words: Aluminum alloy, Lap welding, Laser welding, Preheating, Welding parameters