Influence Of Helium-Argon Shielding Gases On Laser-MIG Hybrid Welding Of A7N01 Aluminum Alloy

Laser-arc hybrid welding technology combines the advantages of laser welding and arc welding.The technology is bound to be widely used in the industrial field for its advantages of lower heat input,small deformation,high welding speed and wide adaptability.The main element of aluminum alloy is Al-Zn-Mg,which has the advantages of small specific gravity,high specific strength,easy processing and forming,no magnetic,no low-temperature transitions,so,it has become the main high-strength light material in industrial application.However,the low energy absorption and porosity defects in aluminum alloy welding are still the main problems of laser-arc hybrid welding.In this paper,different proportions of a mixed helium-argon shielding gas were used to reduce the porosity defects of the weld,while,an improvement of the energy absorption rate and an increased weld penetration were achieved.In order to research the effect of different protective gases on the characteristics of laser-pulse MIG hybrid welding,a series of theoretical analysis and experimental research were made,which mainly consist of the four aspects of plasma characteristics,droplet behavior,weld formation and porosity defects.The characteristics of laser welding,pulse-MIG welding and laser-pulse MIG hybrid welding were researched by high-speed photography and spectrometer.The plasma temperature and electron density were calculated by the Boltzman mapping method and the Stark broadening method.It is found that the plasma temperature and electron density of hybrid welding is the highest,the pulse MIG welding is second,the laser welding is the lowest,and the stability of plasma and droplet transfer is the best of the hybrid welding.Then this paper focused on the influence of different proportions of helium-argon mixed shielding gas on the plasma morphology and droplet behavior of laser-pulse MIG hybrid welding.The test results have shown that the arc and laser plasma are obviously compressed at the surface of the molten pool by the increase of the helium composition of the shielding gas,further,decreased the distance between the end of the wire and the molten pool,the short circuiting transition is easily formed.If the helium content exceeds 50%,the arc combuste unstabitily and droplet transformed difficultly,thus,the welding process is unstable and the weld formation is poor.It is found that with increasing helium content,the spectral intensity decreases,and the plasma temperature and electron density both decrease.The weld penetration increased with the increase of helium content.When high purity helium was used as shielding gas,the inclination of the keyhole was large,which increased the absorption coefficient of Fresnel and got the maximum weld penetration depth which was about 1.6 times higher than the penetration depth reached by high purity argon protection.The energy of the laser keyhole is absorbed by the Fresnel of the hole wall and change the weld penetration.The effects of inverse bremsstrahlung absorption,refraction and scattering on the plasma were calculated.It is found that the energy loss of the fiber laser was very small by inverse toughening absorption and refraction.The addition of helium in shielding gas can enhance the stability of the keyhole during welding process,hereby reducing porosity of the weld.With increasing helium gas ratio of the helium-argon mixture,the porosity of the weld decreases gradually.While the helium gas composition reaches values higher than 50%,there is no noticeable change in the porosity of the weld,and the porosity of the weld seam is 80% lower than that of high-pure argon.