| Hot-Wire Tungsten Inert Gas Welding(HW-TIG)is a novel process based on TIG welding,with relatively high-efficient and low-cost.In high-speed HW-TIG welding,undercut,hump and other weld forming defects may occur in the weld,which hinders the improvement of welding production efficiency.In this study,an external transverse magnetic field(ETMF)is introduced into the high-speed HW-TIG welding process to suppress the occurrence of defects such as undercut and hump.Through a combination of welding experiments and numerical simulation,the mechanism of the ETMF on the temperature field,the morphology of molten pool and the behavior of liquid metal in the molten pool during the welding process is explored,to provide a theoretical basis for the ETMF to improve the formation of high-speed HW-TIG welds and the quality of joints.The research content of this article has strong theoretical significance and engineering practical value.In this study,a transverse magnetic field generator is designed,manufactured and tested.A welding test platform was built for a 4 mm thick Q235 steel plate,and a high-speed HW-TIG surfacing test with or without an ETMF was carried out to study the macro morphology,microstructure,microhardness and corrosion resistance of the welded joint.To address the problem of insufficient adjustment accuracy of the first-generation magnetic field generator,the second-generation magnetic field generator was manufactured and introduced into the HWTIG butt welding process.The high-speed development of the 2 mm thick Q235 steel plate with or without an ETMF the HW-TIG butt joint test also analyzes the macroscopic morphology,microstructure,microhardness and corrosion resistance of the welded joint.On this basis,the HW-TIG numerical analysis model with or without an ETMF is established,and the FLUENT commercial software is used to simulate and calculate the temperature field and molten pool flow field of HW-TIG surfacing welding with or without an ETMF.The results of the analysis of the macroscopic appearance of the weld show that in the surfacing test,the ETMF can significantly suppress the undercut and hump defects that occur during the high-speed HW-TIG welding process,and improve the weld formation;in the butt test,the weld is not applied with a magnetic field.The phenomenon of non-penetration appears.After the introduction of an ETMF,the phenomenon of weld non-penetration is significantly improved,and the welding quality is significantly improved.The microstructure analysis results show that when no magnetic field is applied,there is a coarse ferrite structure in the weld area,which points from the fusion line to the weld surface.In addition,there are Widmanstatten(W)structure and acicular ferrite in the weld area.After the ETMF is introduced,the dendritic ferrite and W structure in the weld area are broken under the stirring action of the molten pool caused by the magnetic field,the amount of hardened martensite structure is reduced,and the structure in the weld area is refine and uniform with a dispersed distribution.The microhardness analysis results show that when no magnetic field is applied,the hardness value of the weld area is higher,and the hardness of the base material area is the lowest.After the introduction of the ETMF,the hardness of the weld zone decreased slightly,and the hardness of the heat-affected zone and the base metal area remained basically unchanged.Specifically,the hardness value of the weld zone of the build-up welding joint is reduced by about 40 HV10 compared with the case without a magnetic field,and the hardness value of the weld zone of the butt joint is reduced by about 55 HV10 compared with the case when the magnetic field is not applied.The corrosion resistance analysis results show that in the surfacing experiment,the average corrosion rate of welded joints without magnetic field surfacing is 0.034 mm/y,and the average corrosion rate of welded joints with ETMF surfacing welding is 0.055 mm/y.The average corrosion rate of welds is 1.61 times the average corrosion rate of welds with an ETMF;in the butt joint test,when only the weld area is reserved for electrochemical test analysis,the average corrosion rate of the base metal is 0.012 mm/y,without adding the average corrosion rate of welds under a magnetic field is 0.130 mm/y,and the average corrosion rate of welds under a transverse magnetic field is 0.054 mm/y.The average corrosion rate of welds without a magnetic field is 2.41 times that of welds with an ETMF.The welded joints with transverse magnetic field have better corrosion resistance.HW-TIG surfacing welding temperature field results show that when no magnetic field is applied,when the peak temperature of the molten pool reaches the liquidus temperature of the base material at 0.32 s,the molten pool begins to appear,and the welding process reaches the quasi-steady state stage at 2.3 s,and the peak temperature reaches 2190 K,remove the heat source,the temperature drops below the liquidus after 6.22 s,and the peak temperature drops below the solidus at 6.38 s.Under the action of the applied magnetic induction intensity B=4m T,the molten pool appears in 0.26 s,and the molten pool enters the quasi-steady state in 2.2s under the external magnetic field,and the maximum temperature of the quasi-steady state is2260 K;after the heat source is removed,the maximum temperature decreases in 6.26 s Below the liquidus,the maximum temperature drops below the solidus at 6.42 s,and the molten pool is completely solidified.Through the thermal cycle curve of each point on the center line of the weld and the center line of the vertical weld,it can be found that the thermal cycle curve of each point on the center line of the weld is basically the same;the peak temperature of each point and the time and distance welding to reach the peak temperature The distance of the seam center line is proportional.The flow field results show that in the quasi-steady state stage at 4.0 s,the overall flow trend of the upper surface of the molten pool without a magnetic field is that the liquid metal diffuses from the center to the surroundings,and then flows back to the central area of the molten pool along the edge of the molten pool;the longitudinal section of the molten pool The liquid metal presents two different circulation movements before and after the molten pool.The liquid metal at the front of the molten pool forms a clockwise circulation,and the tail of the molten pool forms a counterclockwise circulation.The maximum backward velocity of the liquid metal flow at the front of the longitudinal section of the molten pool is 0.054 m/s.The flow on the upper surface of the molten pool with an ETMF has an overall forward flow trend,that is,consistent with the welding direction,the circulation at the tail of the molten pool becomes smaller;the flow trend of the longitudinal section of the molten pool changes significantly,and the flow of liquid metal at the front of the longitudinal section of the molten pool is the flow velocity is reduced to 0.042 m/s.The decrease in the kinetic energy of the backward liquid metal flow rate is conducive to the uniform mixing of the molten base metal and the weld deposited metal,and promotes the uniform spread of the liquid metal in the molten pool,thereby effectively suppressing the occurrence of hump and undercut defects,and making the weld continuous.Beautiful,the microstructure of the welded joint obtained after welding is more uniform and stable. |
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