Simulation Of TIG Welding Arc Characteristics And Its Effect On Microstructure Of 5A03 Weld Under Alternating Ar-He Gas Supply Conditions

With the development of welding technology and the wide application of aluminum alloy in aerospace,shipbuilding and other fields,improving the welding productivity of aluminum alloy,improving the quality of materials after welding and its mechanical properties has become the focus of attention.Aiming at the existing problems of traditional TIG welding,such as limited current carrying capacity of tungsten electrode and low welding efficiency,this study proposed a TIG welding method based on traditional TIG welding with alternating Ar-He gas supply.During the process of welding aluminum alloy with alternating Ar-He gas supply,the arc presented a unique dynamic arc characteristic.In order to investigate the arc characteristics of alternating Ar-He gas supply TIG welding and its influence on the microstructure and properties of the weld.In this paper,numerical simulation and experimental verification were used to study the characteristics of TIG arc under 2 Hz alternating Ar-He gas supply.The effect of arc characteristics on microstructure and properties of 5A03 aluminum alloy weld under Ar-He alternating gas supply was studied.FLUENT software was used to conduct finite element analysis on the component distribution and flow situation of Ar and He in the process of alternating transmission pipeline to TIG welding gun,and further simulate the arc characteristics under the condition of 2 Hz Ar-He alternating gas supply.The characteristics of shielding gas distribution,arc temperature field distribution,current density and potential distribution and arc pressure distribution in arc space are obtained.The simulation results are partially verified by arc shape collected by high-speed camera and arc pressure test of water-cooled copper plate.In the process of Ar-He alternating gas supply TIG welding,the arc characteristics have obvious periodic dynamic changes,and the arc shape shows alternating changes of Ar arc and He arc.The specific performance is as follows:the arc temperature changes from 17054 K to 24057 K,and the arc temperature increases obviously;The arc potential increases from 15.84 V to 25.64 V,the maximum potential is reached in the presence of He arc,and the maximum current density at the tungsten tip is 9.46E+7 A/m².The arc pressure varies from 133.99 Pa in Ar arc to 81.74 Pa in He arc.This variable arc characteristic exists in the whole Ar-He alternating gas TIG welding.The influence of arc characteristics of Ar-He alternating gas supply on welding process,weld forming and post-welding quality of 5A03 aluminum alloy was investigated.Through the analysis of the structure and properties of the welded joints under the traditional Ar+He TIG welding and the 2 Hz Ar-He alternating gas supply TIG welding,it is concluded that:Under the same welding parameters,the penetration rate of the welded joint is significantly improved by the alternating gas supply welding method,and the penetration width of the upper and lower surfaces is increased by 0.76 mm and 1.79mm,respectively,compared with the traditional gas supply.XRD analysis shows that the second phase is Al₈Mg₅ in the weld zone under the two gas suppy modes.By BSE,SEM and EBSD analysis,the second phase Al₈Mg₅ in the weld presented a dispersive distribution,and the distribution was finer and more uniform.The grain size in the weld zone decreased from 40.24μm to 38.36μm,and the grain size was obviously refined.According to the mechanical properties test,the mechanical properties of welded joints under alternating gas supply are significantly improved,the average hardness of welded joints is increased by 13.16%,the average tensile strength is increased by 15.05%,and the average elongation is increased by 1.75%.SEM analysis of weld fracture shows that the number of dimples in the weld fracture under the condition of alternating gas supply is significantly higher than that of the traditional weld,and the size is smaller.In summary,under the condition of 2 Hz Ar-He alternating gas supply,the welded joint can obtain better mechanical properties due to its unique arc characteristics.