| In the industrial production,the welding of the thick plate is mainly carried out by the way of machining groove,but the penetration of traditional TIG welding is shallow,so the efficiency for root welding is low.In order to improve the efficiency of groove welding,this subject adopted the GPCA-TIG welding to carry out the preliminary research.Through the welding process test,the influence of characteristic process parameters on weld formation and microstructure was analyzed.Based on this,the influence of groove on arc characteristics was studied,and the main mechanism of weld penetration of the grooved GPCA-TIG welding was analyzed based on the oxygen content in the weld.These studies will further promote the promotion and application of GPCA-TIG welding.The results of the welding process test indicate that many parameters,such as welding current,reactive gas flow,arc length,groove shape,assembly quality,etc.,have a significant effect on weld formation.For the 90° V-shaped groove,when the process parameters are current 180 A,welding speed 50mm/min,oxygen flow rate 0.8L/min,argon flow rate 10L/min,arc length 2.5mm,the increased penetration is the most obvious,but the increase is less than the welding without groove.The microstructure of the weld consists mainly of austenite and ferrite,which are basically the same as those microstructure of weld without groove,but the grain near the groove side surface is relatively coarse.The hardness distribution is similar to that welding without groove,and the weld hardness is higher than that of the base metal.The arc characteristic measurement results show that the groove has a significant effect on the arc shape,arc voltage,and current density,arc pressure and temperature distribution on the anode plate.The arc is formed in groove,and the binding effect of the side surface on the arc changes with the angle of the groove,the welding current,the arc length,and so on,and the arc will thus exhibit different shapes.The distance between the groove side surface and the arc is smaller than the distance between the root of the groove and the arc,so the actual arc length is short,and the arc voltage is small.Current density distribution varies with the groove angle.The current density in the small angle(90°)groove shows a bimodal distribution,and a single peak distribution in large angle(120°)groove.The arc pressure fits the Gaussian distribution,and the pressure peak is located directly below the tungsten electrode.The influence of the welding current on the arc pressure shows a different law with the change of the groove angle.The outer oxygen flow has no significant effect on current density and arc pressure.The temperature distribution is similar to the current density distribution.The peak temperature of small angle(90°)groove is at the side surface,and thepeak temperature of large angle(120°)groove is at the groove center.Based on the arc characteristics study and oxygen content test results,the mechanism of the penetration variation in grooved GPCA-TIG welding was analyzed.It is considered that the surface tension temperature coefficient of the molten pool changes from negative to positive due to the introduction of active elemental oxygen in grooved GPCA-TIG welding,and then a Marangoni convection that flows inward is formed,and the penetration depth increases significantly.However,the presence of the groove causes the current density peak and temperature peak on the arc anode plate to be transferred to the groove side surface,which makes the inward and downward Marangoni convection of the molten pool surface weakened.The electromagnetic force weakening of the arc center also makes the downward circulation caused by the electromagnetic force in molten pool center weakened.All these result in a significant increase in the penetration of grooved GPCA-TIG welding,but the increase is less than that without groove. |
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