Surface Tension Measurement And Study On Penetration Depth Increasing Mechanism Of Stainless Steel In A-TIG Welding

As a new welding method,A-TIG welding can greatly improve the weld penetration depth compared with traditional TIG welding.In stainless steel welding,it can effectively reduce welding deformation and thermal stress concentration,etc,and has been widely used.However,there is no effective method to measure the surface tension of the molten metal.The law of the surface tension of molten metal is unclear.There is no unified understanding of the mechanism of the increasing penetration depth of A-TIG welding.Moreover,the optimization of multi-component active flux formulations is mostly through orthogonal experiments,and there is some blindness.In this context,using the oscillation principle,a method is developed to measure the surface tension of molten metal of stainless steel during A-TIG welding for different active fluxes and studyed the mechanism of increasing penetration depth of A-TIG welding.Firstly,an experimental system is set up for measuring the surface tension of stainless steel and arc behavior in A-TIG welding based on the oscillation principle and laser-vision method.Secondly,the surface tension,arc width,arc voltage,and arc spectrum information is measured during A-TIG for the single component active flux?oxide,fluoride,chloride?.The results suggest that the oxide active fluxes cause the surface tension temperature gradient of the molten metal to change from negative to positive,which will cause the Marangoni convection mode to change.The oxygen released from the decomposition of oxides is the dominant factor contributing to the change of the surface tension.SiO₂,B₂O₃,Cr₂O₃ can cause the arc constriction,resulting in an increase of arc voltage.Both the change of the surface tension temperature gradient and arc constriction under the oxide active fluxes can promote the increase of the penetration depth,however,the change of the surface tension temperature gradient of the molten metal dominate.The chloride?NaCl?active flux does not change the surface tension temperature gradient of the molten metal but causes the arc constriction.The arc constriction under the chloride active fluxes promotes the increase of weld penetration.Fluoride?CaF₂,MgF₂,NaF,Na₃AlF₆?active flux can decrease the absolute value of the surface tension of the molten metal,and the effect on the surface tension temperature gradient is not consistent.Under alkaline-earth metal fluoride?CaF₂,MgF₂?,when the current is small,the surface tension temperature gradient of the molten metal is negative.When the current reaches a certain value,the surface tension temperature gradient of the molten metal changes from negative to positive.Under alkali metal fluoride?NaF,Na₃AlF₆?,the surface tension temperature gradient of the molten metal changes from negative to positive.Fluoride causes the Marangoni convection effect to be significantly weaker than oxide.Alkaline-earth metal fluoride makes the arc expand,and alkali metal fluoride makes the arc constriction.The main reason of increase the penetration depth for the fluoride active fluxes is the increase of flow velocity of molte metal.Finally,three typical active fluxes?TiO₂,NaCl,CaF₂?were selected in pairs to study the change law of the surface tension of mental metal and the arc behavior for different ratios of two-component active fluxes.The result show that when the two-component active flux is TiO₂and CaF₂,,the surface tension temperature gradient changes from negative to positive and the surface tension gradient coefficient becomes large with the content of TiO₂ increasing in two-component active flux.The weld penetration depth is the largest under TiO₂-70%+CaF₂-30%.TiO₂ changes the surface tension gradient of the molten metal,and CaF₂ increases the flow velocity of the molten pool in two-component active flux.So the increase of the penetration depth of the two-component active flux is the result of the combined effect of the change of the surface tension temperature gradient and the increase of the flow velocity of molten metal.When the two-component active flux is TiO₂ and NaCl,the weld penetration depth is the largest under TiO₂-70%+NaCl-30%.the surface tension temperature gradient changes from negative to positive with the content of TiO₂ increasing and the arc width gradually decreases with the content of NaCl increasing in two-component active flux.TiO₂ changes the surface tension temperature gradient of the molten metal and NaCl causes the arc constriction in two-component active flux.The increase of penetration depth is the result of the combined effect of the change of the surface tension temperature gradient and arc contriction.When the two-component active flux is CaF₂ and NaCl,The surface tension temperature gradient of the molten metal does not change.CaF₂ increases the flow velocity of the molten meal.NaCl causes the arc constriction.The increase of the penetration depth is the result of the increase of flow velocity of the molten metal and the arc constriction.The two-component active flux has a synergistic effect on increasing penetration depth.