| 6005A is an Al-Mg-Si series aluminum alloy with excellent comprehensive properties such as low density,high strength,strong corrosion resistance,and easy processing and forming.It is the main lightweight and high-strength material for high-speed train body.Laserarc hybrid welding technology combines the advantages of single laser welding and arc welding.It has the advantages of fast welding speed,small welding deformation,and high weld quality.It has a wide range of application prospects in the welding of high-speed train aluminum alloy bodies.Stomatal defects are a common problem in laser-arc hybrid welding of aluminum alloys,and are closely related to the keyhole stability during laser welding.To this end,this paper proposes a pulsed laser-arc hybrid welding method for aluminum alloys,and attempts to use the pulse oscillation behavior of the laser beam to improve the stability of the welding process,solve the problem of weld porosity,and improve the quality of aluminum alloy composite welded joints.Firstly,based on high-speed camera and NI electrical signal acquisition equipment,the influence laws of electrical signal parameters,droplet transfer and composite plasma behavior under pulsed laser-arc hybrid welding and continuous laser-arc hybrid welding were comparatively studied.The results show that the interaction between the pulsed laser and the arc is significantly weaker than that of the continuous laser.After the pulsed laser is combined,the expansion of the plasma is weakened,the diffusion range is significantly reduced,and the average cross-sectional area of the combined plasma is reduced.In addition,compared with the continuous laser,the peak current is larger in the pulsed laser mode,and the increase of the welding current will significantly increase the electromagnetic force F＿em,promote the droplet transfer,and reduce the transition phenomenon of “two pulses and one droplet” during the welding process.The influence of pulsed laser parameters on the opening and closing behavior of the keyhole surface and the internal dynamic behavior of the keyhole was further analyzed,and the mechanism of the pulsed laser inhibiting the generation of pores was revealed.The results show that the diameter and depth of the CW laser keyhole have large fluctuations,and the keyhole openings are closed more times;in the pulsed laser mode,appropriate process parameters can maintain the stable opening state of the keyhole and reduce the number of keyhole closures,it can also suppress the fluctuation of keyhole depth and improve the stability of the keyhole.The mechanism of blowhole elimination is mainly the following two points:on the one hand,the pulsed laser improves the stability of the keyhole;on the other hand,due to the characteristics of the pulsed laser,the new keyhole in the adjacent cycle can "cut" the old keyhole,so that the liquid metal in the molten pool can be "cut".Backfilling of pores or air bubbles reduces weld porosity.Welding experiments were carried out using optimized pulsed laser parameters(pulse frequency 70 Hz,duty cycle 80%)and continuous laser parameters.Compared with the continuous laser,the surface of the aluminum alloy weld is well formed under this pulsed laser parameter,the weld porosity is reduced from 3.96% to 0.92%,and the weld penetration is increased from 3.77 mm to 4.38mm;the current under this pulsed laser parameter The coefficient of variation of voltage,the coefficient of variation of the composite plasma crosssectional area,the coefficient of variation of the keyhole diameter and the coefficient of variation of the keyhole depth are all smaller than those of the CW laser parameters,indicating that the stability of the hybrid welding process under this parameter is better than that of the CW laser-MIG hybrid welding.In the butt test,the porosity of the pulsed laser-MIG composite welded joint was as low as 0.42%,and the tensile properties were excellent(the joint coefficient was 69%).The comprehensive mechanical properties of the welded joint obtained under this parameter were the best. |
