Research On The Properties Of The Welds Of 5A06 Aluminum Alloy In TIG Welding Under Variable Gas Supply

5A06 aluminum alloy has the characteristics of good corrosion resistance and high specific strength,which is widely used in aerospace and other fields.In the production process of aluminum alloy thin plate welding,tungsten inert gas welding(TIG)is the preferred welding method.The traditional TIG welding shielding method with continuous gas supply system has a lot of problems during the production of aluminum alloy thin plate welding,such as the limited current-carrying capacity of tungsten electrodes,low production efficiency,coarse joint weld grains,and low strength.For those reasons,a new method of aluminum alloy variable gas supply TIG welding in this thesis is proposed to improve the property of its weld by using arc pressure with cyclical changes,and also as a reference for industrial application of 5A06 aluminum alloy TIG welding.In this paper,a special arc force test device was used to measure and then analyze the change of the arc pressure of gas-supplied welding with different cycles.By comparing the traditional gas supply and variable gas supply under different cycles method in the aspect of TIG welding arc force(radial arc pressure and arc center pressure).It is found that the maximum arc pressure is at the arc center,as the distance from the arc center increases,the arc pressure gradually decreases.The maximum arc center pressure of the TIG welding arc in the traditional gas supply mode is a constant value of 116.9 Pa,and the arc center pressure in the variable gas supply mode changes cyclically,and the arc center pressure value of the welding arc(123 Pa)has been achieved the highest under the condition of a fluctuation cycle of 0.125 s.The arc figure of TIG welding with variable gas supply was recorded by high-speed camera,and the influence of variable gas supply on arc figure,weld depth and width was analyzed.The results show that the arc diameter of TIG welding with variable gas supply mode is significantly reduced compared with that of traditional gas supply mode.When the fluctuation cycle is 0.125 s,the welding arc diameter is the smallest,no pore is found in the cross-section of weld,also the penetration depth and width ratio are larger.Therefore,the fluctuation cycle 0.125 s was selected as the optimal variable gas supply cycle parameter.The microstructure of 5A06 aluminum alloy TIG welded seam was compared and analyzed under variable gas supply conditions with fluctuation cycle of 0.125 s and traditional continuous gas supply conditions.It is found that the welding arc force caused by the fluctuating gas supply directly acts on the molten pool in the form of fluctuating pressure,which makes the microstructure of the welded seam change significantly.Under traditional continuous aeration conditions,the?(Al₃Mg₂)phase in the central microstructure of the weld is randomly distributed on the?phase(Al matrix)and is in the shape of a fishbone.The microstructure of the weld under variable gas supply is characterized by fine particles or long strips of?(Al₃Mg₂)phase uniformly dispersed on the?phase.The average grain diameter at the center of the weld under the traditional method is 35.68?m,and the average grain diameter at the center of the weld under the variable gas supply method is 25.88?m,the average grain size of the weld specimen under the variable gas supply is smaller,the central crystal grains are all equiaxed crystals.The mechanical properties of the welded joints and the corrosion resistance of the welds under the conditions of traditional gas supply and variable gas supply with a fluctuation cycle of 0.125 s were compared.The results show that:compared with the traditional gas supply,the tensile strength of the welded joint under the variable gas supply condition is increased by 14.2%,and the elongation rate is increased by 12.1%,and all tensile specimens have ductile fracture at the weld.The average hardness of the weld under traditional gas supply is 80.44 HV,however,the average hardness of the weld under the variable gas supply is 84.70HV,which is increased by 5.3%.In 3.5%Na Cl solution under room temperature,the self-corrosion current densities of variable gas TIG weld and traditional weld are 0.002896 A·cm^-2and 0.001325 A·cm^-2,respectively,the self-corrosion current density of the welding seam of variable gas supply TIG welding is slightly higher,and the corrosion rate is also slightly faster.The electrochemical reaction resistance of the TIG welding seam under the variable gas supply condition is smaller than that of the traditional gas supply welding seam,the corrosion resistance of welds under variable gas supply is slightly lower than that under the traditional gas supply.