Study On Arc Shape And Weld Formation Of Magnetically Controlled K-TIG Welding

Keyhole Tungsten Inert Gas(K-TIG)welding is a new and efficient welding method.It can use high current for welding,and the welding current can reach 1000 A,which can generate arcs with high energy,high stiffness and strong penetrating power.Without filling the welding consumables and opening the groove,a metal sheet with a thickness of 3-16 mm can be penetrated at a time to realize single-sided welding and double-sided forming,which greatly improves the welding efficiency.Q345 R steel is often used as the raw material for pressure vessels,and its thickness is generally relatively thick.The traditional welding method is used for welding,which generally requires multi-layer and multi-pass welding.When using K-TIG welding to weld Q345 R steel,although the welding efficiency and cost are solved,the weld formation is prone to undercut defects on both sides.The application range of magnetron welding technology is becoming wider and wider.Applying a magnetic field during the welding process can effectively improve the mass and heat transfer behavior of the liquid metal in the molten pool,refine the grains of the microstructure,and reduce defects such as pores and thermal cracks.In this study,the longitudinal magnetic field was applied to the K-TIG welding of Q345 R steel.By changing the magnetic field parameters,the effect of the longitudinal magnetic field on the K-TIG welding arc shape,weld formation,welded joint structure and impact properties was studied.In this study,the CCD camera was used to observe the shape of the K-TIG welding arc under the action of a longitudinal magnetic field,and the changes in the shape of the K-TIG welding arc under different magnetic field parameters were obtained and analyzed.The test results show that: under the action of a longitudinal magnetic field,the shape of the K-TIG welding arc presents a smaller bell shape than when there is no magnetic field.As the magnetic field strength increases,the phenomenon of arc contraction is more obvious;as the frequency of the magnetic field increases,the arc shape tends to be more stable and the stability improves.Under the action of the longitudinal magnetic field,the threshold welding current of the base metal penetration can be reduced,and the maximum can be reduced by about 40 A.Under the action of the DC longitudinal magnetic field,due to the directional Lorentz force of the liquid metal in the molten pool,the forming quality of the left side of the weld is significantly improved compared with that without a magnetic field,but the undercut phenomenon on the right side of the weld is more obvious than when there is no magnetic field.Under the action of the AC longitudinal magnetic field,it is beneficial to reduce the weld width and improve the undercut defects on both sides of the weld.With the increase in the strength of the AC longitudinal magnetic field or the frequency of the magnetic field,the improvement effect of weld formation becomes more and more significant,and the weld forming becomes smooth and uniform.Under the action of the longitudinal magnetic field,both the welding arc and the molten metal in the molten pool will be affected by the Lorentz force,both of which intensify the flow of the molten metal in the molten pool,produce the effect of electromagnetic stirring the molten pool which can refine the K-TIG welded joint structure,and is beneficial to reduce the content of coarse proeutectoid ferrite(PF)and widmanstatten(W)structure,and improve the impact performance of the joint.However,when the optimal value of the magnetic field parameter is exceeded,the content of massive ferrite and widmanstatten structure increases instead,resulting in a decrease in impact performance.