Simulation And Experiment Study Of PPCA-TIG Welding Based On Cathode Spots

TIG welding is a common welding method for aluminum alloys.However,its low welding efficiency,high cost and shallow weld penetration limit the development.The Powder Pool Coupled Activated TIG welding（PPCA-TIG welding,Powder Pool Coupled Activating TIG welding）can deliver the active agent powder to the arc-pool coupling system by the outer gas.The interaction between the arc and the molten pool metal introduces active elements that increase the depth of melt and improve the properties of the weld seam,which can not only achieve the welding of aluminum and magnesium alloy,but also facilitate the automation of the welding process.In this paper,using AC TIG and PPCA-TIG welding to weld 3003 aluminum alloy.Filming the periodic behavior of cathode spots of different active agents under different process parameters by high-speed camera equipment.Then through the experiment to analyze the influence law and mechanism of process parameters and active agent changes on the behavior of cathode spots;Based on FLUENT,establishing the transient models of AC TIG and PPCA-TIG weld pools considering the behavior of cathode spots and investigating the influence of driving force on the pool flow by numerical simulation,Finally,it was studied the weld depth to width ratio and the mechanical properties of the joints under different process parameters.This is important to clarify the mechanism of melt pool flow and melt depth increase in PPCA-TIG welding and to promote the research of PPCA-TIG.The behavior of cathode spots under the same process parameters was analyzed,which can find that the addition of active agent affects the motion behavior of surface cathode spots.Among them,the effect of SiO₂ on cathode spots is particularly obvious.The cathode spots of TIG welding are first produced on the oxide film at the edge of the molten pool,then move toward the center of the molten pool,and finally will be uniformly distributed at the edge of the molten pool.Unlike TIG welding,the cathode spots under active agent SiO₂ and MnCl₂ are produced on both the oxide film and the slag to a much wider extent,and on slag at the periphery of the molten pool.Under different process parameters,when the current increases,the arc length decreases,and the outer gas flow increases,the motion behavior of the cathode spot remains the same,but the number increases.The addition of active agent during welding caused the cathode spot to shrink considerably which can make the axial temperature at the center of the arc increased significantly and the addition of SiO₂ had a more pronounced effect than the addition of MnCl₂.The number of cathode spots is ranked as PPCA-TIG-MnCl₂<TIG<PPCA-TIG-SiO₂.The AC TIG welding and PPCA-TIG welding pool models considering the cathode spot are established and numerically simulated to obtain the distribution of the temperature and flow fields of the pool.The temperature field distribution on the upper surface of the molten pool is not uniform and the location of the high temperature is the location of the cathode spot.The location where the cathode spot exists,the distribution of the temperature field and flow field of the molten pool will be non-uniform and the temperature value at the cathode spot is higher than the surrounding area.Secondly,according to the driving force of the molten pool,studying the flow behavior of the pool under the driving force of AC TIG and PPCA-TIG welding pool.Electromagnetic force and surface tension are the main driving forces that drive the variation of melt depth and width of the melt pool.The electromagnetic force drives the melt pool flow from the edge of the melt pool to the center of the melt pool,making the melt depth increase and the melt width decrease.The surface tension decreases the melt depth and increases the melt width.The increase in depth of the melt for PPCA-TIG welding is greater than that for TIG welding,while the difference in the change in melt width is not significant.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 rate is 12 L·min^-1,the outer gas flow rate is 8 L·min^-1,and the motor speed is 30 r·min^-1,using active agent SiO₂,it is possible to weld through 8 mm thick 3003 aluminum alloy plate in one pass and the weld depth can be2.4 times that of conventional TIG welding using active agent MnCl₂.Based on the control variable method,the weld depth-to-width ratio was maximized when the welding current was 160 A with the active agent SiO₂ and the welding current was 170 A with the active agent MnCl₂.When the welding speed is100 mm·min^-1,the arc length is 2 mm and the outer air flow rate is 12 L·min^-1,the weld depth to width ratio under both active agents SiO₂ and MnCl₂ reaches the maximum;The increase in the particle size of the active agent is conducive to improving the weld surface formation,but the effect of increasing the weld depth is weakened.SiO₂ has a greater depth to width ratio than MnCl₂ and the weld surface formation is better with MnCl₂ than with SiO₂;The tensile strength is significantly lower with the addition of active agent SiO₂than without;The hardness is greater in the weld than in the base material,the base material than in the heat affected zone.The hardness of the weld with the active agent is greater than that of the weld without the addition of the active agent.