Effect Of Different Active Fluxes On Thermophysical Behavior Of Arc And Weld Pool During TIG Welding Process

Active tungsten inert gas(A-TIG)welding is a special TIG welding method which has the outstanding advantages of greatly increasing the weld penetration depth,increasing production efficiency and improving the weld formation.It has a broad application prospect in industrial production,however,the lack of a unified explanation for the mechanism of penetration increasing restricts its further application in the industrial field.At present,the theory of arc constriction or the theory of surface tension altering is widely utilized to account for the increasing of the weld penetration by many researchers,but there are great differences in the research results.Arc constriction theory is mainly studied by the observation of arc shape and numerical simulation.The results of these researches are influenced by experimental equipment and model assumptions,giving rise to great differences in conclusions.The theory of surface tension altering mainly supported by means of numerical simulation and the observation of motion trail of tracer particles.Simulation results are particularly sensitive to model assumptions,and the differences of actual welding conditions are significant,the method of tracer particle is used to detect the direction of fluid flow of molten pool,which can't obtain the data of surface tension of liquid metal,and can't clearly understand the rule of the surface tension altering in molten pool;Moreover,the existing works are not integrating the thermal physical behavior of arc and weld pool,so that the mechanism of A-TIG welding penetration depth increasing hasn't formed an unified explanation.Firstly,a measuring system of arc space spectrum,arc shape and arc voltage,surface temperature and oscillation frequency of molten pool is built.The information of these parameters is collected and the influence of different active fluxes on the thermal physical behavior of TIG welding arc and weld pool is studiedSecondly,the effects of different active fluxes on the arc space spectrum characteristics and arc temperature field of TIG arc are studied by using the arc space spectrum,arc morphology and voltage acquisition system.The results show that Ti O₂has slight effect on the behavior and temperature field of TIG welding arc.The vapor of B₂O₃ and Si O₂ permeates the arc space during welding and cause the rise of arc voltage and phenomenon of arc constriction.The arc constriction caused by B₂O₃ and Si O₂ has little effect on the whole arc temperature field.Chloride active particles(Na?)are spread all over the arc space,resulting in the constriction of arc morphology and the increase of arc voltage.The arc constriction causes the concentration of arc temperature field,which makes the electron temperature near the cathode region,the arc column region and the anode region rise greatly.Fluoride active particles(Al?,Mg?,Ca?)are also spread all over the arc space,causing the increase of arc voltage,but there are no constriction phenomenon of the arc morphology observed.All of the fluoride active fluxes increase the electron temperature near the anode area,and the raise of temperature is related to the thermo-dissociation of the flux on the molten pool surface and the ionization energy released by the combination of charged particles.Thirdly,the influence of different active fluxes on the pool surface temperature of TIG welding is studied using infrared temperature measurement system.The results show that all of the oxide active fluxes will make the surface temperature of molten pool totally decreased,the overall surface temperature of molten pool corresponding to B₂O₃ and Si O₂ are decreased obviously,and the overall surface temperature of the molten pool corresponding to Ti O₂ is decreased to some extent,which has a significant influence on the surface temperature field of molten pool.The Na Cl active flux will make the temperature of molten pool slightly decreased,and the molten pool surface temperature gradient has no significant change,which has a little effect on the surface temperature field of molten pool.Alkali metal fluoride(Na₃Al F₆)makes the overall surface temperature and its gradient of molten pool decrease obviously.Alkali-earth metal fluoride(Mg F₂,Ca F₂)makes the overall surface temperature and its gradient of molten pool rise,which has a certain influence on the temperature field of the molten pool.Finally,the surface tension measurement system based on the oscillation principle of molten pool is established to study the influence of different active fluxes on the surface tension and the mechanism of weld penetration depth increasing in TIG welding.The results show that the oxide active fluxes can make the temperature gradient coefficient of average surface tension of molten pool changes from negative to positive.The temperature gradient coefficient of average surface tension of molten pool is not changed when using chloride active fluxes.Fluoride active fluxes can make the temperature gradient coefficient of average surface tension of molten pool existing two kinds of state,when the average surface temperature of molten pool is low,the temperature gradient coefficient of average surface tension of molten pool is negative.In contrast,the temperature gradient coefficient of average surface tension of molten pool is positive when the average surface temperature of molten pool is high.Combined with the variation characteristics of arc temperature field and molten pool surface temperature field,it can be concluded that the mechanism of three different active fluxes to increase the weld penetration depth is different.The main reason for the increase of penetration depth of oxide fluxes is the change of surface tension temperature gradient of molten pool.The primary reason for the increase of penetration depth of chloride active fluxes is arc constriction.The dominant reason for the increase of weld penetration depth is that fluoride active fluxes can increase the temperature of arc and molten pool,causing the decrease of the absolute value of molten pool surface tension,and promote the increase of fluid flow rate of molten pool,rather than the constriction of arc.