Numerical Simulation Of TOP-TIG Arc Additive And Microstructure And Properties Of Al Alloy

To realize the rapid forming of arc additive to medium workpiece,the heat source of traditional Tungsten Inert Gas(TIG)welding was used in this project to realize the additive manufacturing of aluminum alloy.The self-made TOP-TIG automatic wire feeding and additive system has been developed in view of the low deposition rate of TIG heat source.Different from traditional TIG welding,the welding wire of this system is fed from the top of the arc and forms a certain angle with the tungsten electrode.For higher additive efficiency,the external magnetic field was used to form an alternating magnetic field in the welding area.The formed magnetic field can directly affect the arc and droplet,improve arc behavior and control droplet transfer.Taken together,these further improve additive efficiency and quality,resulting in high-efficiency TIG additive.There are certain difficulties in measuring and observing the changes in magnetic arc behavior and droplet transfer process since the complex welding area involves the interaction of multifaceted physical quantities.In the present project,we combined high-speed camera with numerical simulation to simplify the partial complex physical process of magnetic control TOP-TIG.Through numerical simulation,the magnetic field distribution and its size are visualized,and establish the relationship between arc temperature distribution and heat transfer.First,a TOP-TIG integrated gun head of sharp angular magnetic field was developed.The sharp angular magnetic field was realized through the combination of an energized solenoid with a long and short magnetic rod,and then the magnetic field was coupled with the arc.The addition position of magnetic field was discussed.The process parameters were adjusted to a long-term contact droplet transfer mode.Aluminum alloy addition was carried out after determining critical welding current and wire feeding speed under the condition of no-magnetic field.Numerical simulation was conducted on the sharp angular magnetic field.The arc will be affected by the sharp angular magnetic field after adding a magnetic rod.The geometric shape of the arc becomes an elliptical one under the action of Lorentz force.The Lorentz force in its long axis direction points outward,leading to arc expansion.The Lorentz force in the short axis direction compresses the arc in the opposite direction.When the spiral tube current is repeatedly reversed to achieve arc constriction,the long and short axes are interchanged.The temperature and velocity fields under the sharp angular magnetic field of the arc were obtained through numerical simulation on the arc.The mechanism of the sharp angular magnetic field on the arc was analyzed,as well as droplet transfer.The effect of the sharp angular magnetic field on charged particles in the arc zone changes the arc behavior and temperature field,allowing the welding wire to obtain more heat,thereby promoting the process of droplet transfer.Second,the formation of 2319 additive components was studied and the results showed that the excitation current in the magnetic field had a significant effect on the formation of deposited bodies,while also improving the deposition efficiency.The magnetic field increased the ratio of effective melt width to total melt width,as well as the thickness of deposited bodies,allowing them to utilize more materials.In addition,the simulation results and high-speed camera analysis showed that,under the effect of magnetic field,alternating deflection of the arc occurred,which improved the the wire feeding speed,leading to an increased deposition efficiency of aluminum alloy.Finally,the microstructure and mechanical properties were studied and the results showed that,the size of columnar crystals gradually increased as the excitation current increased.The fine dispersed second phase was precipitated after heat treatment.The addition of a sharp angular magnetic field significantly increased the maximum tensile strength.The columnar crystals arranged in a single direction are beneficial for improving tensile strength.However,large-sized columnar crystals can deteriorate its performance to a certain extent.The precipitated fine dispersed second phase after heat treatment can improve the mechanical properties at room temperature.In conclusion,the geometric shape of the arc captured by a high-speed camera demonstrated the effectiveness of the sharp angular magnetic field on the arc shape.Based on the distribution of Lorentz force as a simulation result,the size,shape,and position of the conductive rod can be further improved in the future,which is conducive to improving the compression effect of the sharp magnetic field on the arc.