Laser welding performance and process of DP780 galvanized steel

DP780 galvanized dual phase steel used for vehicles with thickness of 0.8 mm was laser welded in lap joint by 4 kW continuous fiber laser. By adjusting the reserved gap between the two plates, laser power, welding speed and defocusing amount, the influence of process parameters on the shaping of welds was studied. Then, the effect of various process parameters on the amount of subsidence, tensile strength, and porosity of welds was analyzed. Finally, the welding quality was evaluated based on the tensile strength, the amount of welds subsidence and the condition of porosity. The results showed that when the power of 3800 W, the welding speed of 95-100 mm/s, the amount of defocusing distance in the -2 mm-+2 mm, leave the reserved gap in the process parameters of the 0.2-0.25 mm conditions, the good welding shaping was achieved. By the above welding parameters, the tensile strength was maintained more than 180 MPa, the total amount of welds subsidence was between 0.35-0.45 mm, and the porosity condition which had splashes and the external porosity was less. The tensile strength -the amount of welds subsidence -the condition of porosity method is proposed to evaluate welding quality, it can improve the porosity defects and the welding efficiency.