Research On Microstructure And Properties Of Copper-steel TIG Welding Joint Based On Applied Magnetic Field

As a widely used metal material,copper and steel composite structure can not only save materials,but also have the advantages of performance and cost,so it has a broad application prospect in the fields of refrigeration device,mechanical manufacturing and automobile industry.There are great differences in chemical composition and physical properties between the two kinds of copper steel materials,so it is easy to form defects such as pores and cracks during welding.TIG welding is widely used because of its excellent economy and flexibility.However,due to its high arc temperature and high temperature residence time,its application in dissimilar metal connection is limited.The longitudinal magnetic field can optimize the TIG arc and improve the mechanical properties of the welded joint effectively.In this paper,HS201 pure copper welding wire is selected,TIG welding method is adopted,and the butt joint test of T2 red copper and Q235 low carbon steel with thickness of 2 mm is carried out by means of external longitudinal magnetic field.In this paper,the effects of welding speed and current on the appearance,microstructure and mechanical properties of TIG welding joint without magnetic field are studied.It is found that the microstructure of the weld is mainly composed of cellular crystals and solute segregation exists in the microstructure of the weld.When the welding current is 95 A and the welding speed is 95 mm/min,the appearance of the welding joint is well formed,the microstructure of the welding joint is fine cellular crystal,and the tensile strength reaches the maximum value ?b=154.7 MPa.Secondly,the effect of external magnetic field on the appearance,microstructure and mechanical properties of TIG welding joint of copper steel dissimilar metal was studied.It is found that the external magnetic field can improve the appearance of the welded joint.After the magnetic field is applied,the microstructure of the weld is finer,and the mechanical properties of the welded joint are improved.Under the condition of DC magnetic field,when the magnetic field strength is 10 m T,the tensile strength value is increased by 25.79% compared with that without magnetic field;under the condition of AC magnetic field,when the magnetic field frequency is 30 Hz and the magnetic field current is 0.4 A,the tensile strength value is increased by 44.47% compared with that without magnetic field.Finally,the influence of magnetic field on the molten pool is analyzed.The AC magnetic field is better than the DC magnetic field in inhibiting the solute segregation.Under the action of DC magnetic field,the magnetic field continuously stirs the molten pool in one direction,and the Fe atoms in the liquid metal can diffuse to the molten pool near the moving track.Under the action of AC magnetic field,the magnetic field intermittently stirs the molten pool clockwise and anticlockwise,which makes the Fe atoms in the liquid metal diffuse to the molten pool more evenly.