Transfer Behavior Of Active Flux On The Surface Of Molten Pool In AC PPCA-TIG Welding Of Aluminum Alloy

Aluminum alloy is widely used for its low density,high strength,high plasticity,easy processing,corrosion resistance and excellent electrical and thermal conductivity,but aluminum alloy welding is still dominated by TIG welding,and TIG welding shallow penetration,low deposition speed,low production efficiency,cumbersome welding process,high cost,low efficiency problems limit its development.Then the proposed The Powder Pool Coupled Active TIG welding（PPCA-TIG welding）,double-layer gas protection design are proposed.Different active agent powder can be selected for different metal materials to realize mechanized automatic welding.In this paper,the 3003 aluminum alloy is welded by AC PPCA-TIG welding.By studying the surface forming of the molten pool under the transition of different active flux and the high temperature resistance of the active flux,the influence of different active fluxs on the surface forming of the weld is analyzed.The effect of different surfactants on arc cathode spots was analyzed by high speed camera.Then,by studying the transition behavior of active elements on the molten pool surface,a transition model of active agent on the molten pool surface was established.These studies are of great significance for the study of the formation mechanism of AC PPCA-TIG welding of aluminum alloy,guiding the development of active material and welding technology,and obtaining welds with significantly increased penetration depth and well-formed surface.When the welding current is 160 A,the welding speed is 100 mm·min^-1,the arc length is 3 mm,the inner gas flow is 12 L·min^-1,the outer gas flow is 8 L·min^-1,and the motor speed of the powder feeder is 30/80 r·min^-1,the AC PPCA-TIG welding of aluminum alloy with single group active agents SiO₂ and MnCl₂ can significantly increase the penetration,especially SiO₂ can weld through 8 mm thick plates.There is welding slag on the surface of both welds,but the weld surface with MnCl₂ as active fiux is relatively good,SiO₂ is poor and the surface is uneven.Through the weld migration test,it is found that the coated surfactant will increase the resistance of the arc conductive channel,and the resistance of the additional conductive channel will increase with the decrease of the gap between the inner edge line of the coated surfactant and the center line of the specimen,and it is found that SiO₂ has a higher welding high temperature resistance than MnCl₂.Through the determination of the metal O content in the molten pool,it was found that the active element O did not enter the molten pool,so the theory of surface tension temperature coefficient change cannot be used as the theoretical basis for the increase of the penetration depth of aluminum alloy PPCA-TIG welding.Then the spot behavior is analyzed.It is found that the anode spot on the metal surface affects the conductive channel of the anode spot due to the high welding temperature resistance of SiO₂ surfactant,which reduces the conductive area and makes the arc shrink.At the same time,it is found that after current zero until stable combustion arc reigniting period,compared with traditional TIG welding,the PPCA-TIG welding arc after current zero to reach stable combustion in a shorter period of time,the cathode spots on the oxide film movement speed faster,clean up the behavior of cathode spots can cause surface arc pit corrosion pits,Lead to uneven surface of weld.For the high-temperature molten pool,the rapid cooling method is used to cool the molten pool under the transition of different active flux,and the distribution of active elements at high temperature can be obtained.Through the comparative analysis of penetration and metallographic results,it is found that the back water spray cooling0.6 s before arc quenching can make the crystal growth extend to the surface of the molten pool without affecting the penetration,which has the best quenching effect.For the welds obtained by the rapid cooling method,the transition behavior of SiO₂ and MnCl₂ single-component flux on the surface of the molten pool was studied by XRD,EDS,AES,XPS,TG/DSC and SEM.It is found that when SiO₂ is used as the active flux for welding,during the process of SiO₂ powder being sent to the arc area by the outer gas of the welding torch,a large amount of SiO₂ powder is affected by the inner protective gas,and the active flux fly away from the welding arc,and only part of the active flux with enough kinetic energy to enter the arc,most of the active flux entering the arc directly adhere to the surface of the molten aluminum alloy,while a small amount of SiO₂ active flux dissociate in the arc space.During the whole transition process,SiO₂ did not participate in the molten pool reaction,and the main reason for the increase in the penetration depth was the influence of its higher welding high temperature resistance on the conduction path.Through the analysis of MnCl₂ transition,it is found that the active flux MnCl₂powder sent to the arc-melt pool coupling system by the powder feeder can be divided into five parts.A part of the MnCl₂ powder is affected by the inner layer of protective gas,so that a large number of active flux particles fly away from the welding arc,and the second part of the active flux is evaporated due to the high temperature of the arc;The combined water makes MnCl₂ react with water,releasing HCl gas,and generating gray-brown Mn₃O₄ that falls on the surface of the molten pool.The fourth part of the MnCl₂ active flux powder enters the arc space in a small amount,and a part of the MnCl₂ powder that enters the arc space is heated,melted and decomposed,dissociated into Mn and Cl,which are excessive to the molten pool in the arc space,and the other part is not completely The evaporated MnCl₂ adheres to the surface of the molten pool in the form of welding slag,especially in the periphery of the arc,there are many activator particles in the form of welding slag.During the whole transition process,the decomposition,evaporation,dissociation and other processes endothermic heat makes the arc shrink,resulting in an increase in the penetration depth,and MnCl₂ will reduce the number of cathode spots,reduce the number of pits produced by cathode spots,and have better surface formation.