Study On The Generation Mechanism Of Pores In 5083 Aluminum Alloy Welding Under Different Arc Atmosphere

With the increasing use of 5083 aluminum alloy in the hull structure of aluminum ship,the problem that the porosity in the 5083 aluminum alloy joint is likely to cause the decrease of the joint performance in the fusion welding process has drawn increasing attention.Usually,it is difficult to achieve the purpose of preventing porosity such as cleaning the base metal before welding or adjusting the welding parameters.In this paper,the 5083 aluminum alloy of 4 mm thickness is welded by changing different shielding gases.At the same time,the formation mechanism of the porosity in the 5083 aluminum alloy joints is analyzed to realize the control of porosityIn this paper,pure argon,pure helium,Ar-He binary gases,Ar-He-CO₂ and Ar-He-N₂ternary gases are used in pulse welding of 5083 aluminum alloy.The characteristics of arc shape and droplet transition under different shielding gas were observed by high speed photography,and the current and voltage signals were collected synchronously.The form of droplet transition under different shielding gas was revealed.Spectral signals were collected from the characteristic points of the arc,and the differences of the spectral signals under different shielding gas were analyzed.The joints were examined by X ray and the porosity was observed.The microstructure of the joint was observed by optical microscope and scanning electron microscope.The mechanical properties of the joint were analyzed by microhardness test and tensile test.In helium-argon binary atmosphere,the energy of the arc to the joint is increased due to the compression effect of helium on the arc.The penetration of the joint will increase with the increasing content of the helium in arc atmosphere.In binary arc atmosphere,the addition of CO₂ and N₂ will not have a significant effect on the penetration,but it will produce an obvious compression effect on the arc.The results of X ray showed that,the joints were not penetrated under pure argon,and the number of pores was higher under pure helium while the parameters were the same.When the proportion of helium in binary arc atmosphere is suitable,the number of pores in the weld is less.While the addition of CO₂ and N₂ in ternary arc atmosphere can effectively reduce the porosity in weld.High speed photography and current and voltage signal test results show that:there is a droplet transfer in 100%Ar and there is a short circuiting transfer in 100%He.There are two transition modes in the helium-argon binary arc atmosphere:spray transfer and short circuit transfer.The droplet transfer mode is a mixed transition between the spray transfer and short circuiting transfer under ternary gases.The porosity of welded joints can be predicted through the information of hydrogen spectrum in spectral signals.Different arc atmospheres have a certain effect on the grain size of the joint area,but the effect of the addition of CO₂ in ternary arc atmosphere is not obvious.Elemental scanning results show that CO₂ and N₂ will not affect the elements inside the joints.After welding,the hardness of the weld seam is the lowest in the joint,which is basically between 55-65HV_0.1,and the hardness of the base metal is the highest.The maximum tensile strength of the joint is 214.4MPa,which is 79%of base metal under the condition of 20%Ar+80%He.The tensile strength of the joint decreases slightly with the addition of CO₂ and N₂ in ternary gases.