Effect Of Alloy Elements On Microstructure And Properties Of Copper-steel Welded Joints

Copper and stainless steel are two kinds of metal materials which are widely used.The composite structure can not only meet the requirements of material performance under different production conditions,but also save the use of copper material,greatly reduce the cost of composite structure,fully play the advantages of the composite structure in the perfor mance and cost.The wide application prospect,and the connection between cathode plate and conducting rod is one of its typical applications.In this paper,the Gas Tungsten Arc Welding（GTAW）method was used to join T2 copper and 316L stainless steel in the form of butt joint,and the welding process parameters of well-formed weld were determined.By filling the weld wire with different alloy elements to the weld,the alloy elements Al and Si pairs of copper and steel were studied.The influence of the mi crostructure of metal welded joint was studied.The effect of alloy elements Al and Si on the mechanical properties of copper steel joints was studied.The effect of alloy elements Al and Si on the electrical conductivity of copper steel joints was studied.The effects of alloy elements Al and Si on the corrosion of copper steel welded joints were studied.The annealing treatment for copper steel welded joint group was studied.The effects of fabric,electrical conductivity and corrosion properties.The butt welding of T2 copper and 316L stainless steel was welded by S201welding wire.Through a large number of process tests,the single side welding and double-sided forming of copper steel dissimilar metal was realized.The weld formation,microstructure morphology and mechanics of copper steel welded joint under different process parameters（welding current,butt gap and arc offset）were studied.Performance and electrical conductivity.The results show that the butt gap has no obvious influence on the weld formation,and the arc bias has a great influence on the weld formation,and the good weld seam can be obtained when the arc is biased toward the copper side.With the increase of heat input,the electric arc agitation increased,the number of rich Fe phas e mixed in the weld metal increased,and the distribution was uneven.The copper steel interface changed from straight to saw-tooth,but the tensile strength of the copper steel joint did not change obviously.The butt welding of T2 copper and 316L stainle ss steel is carried out by three kinds of welding wires,S201,S211 and S214.The microstructure and microstructure of copper steel joint interface were analyzed by SEM,EDS,XRD and other methods.It was found that the addition of Al and Si elements would change the morphology and distribution of the rich Fe phase in the weld.The shape of the rich Fe phase in the weld seam of the S201 welding wire is petal shaped,and the S214 welding wire corresponds to the fine dendrite in the form of the rich Fe phase in the joint weld,and the distribution is not regular,while the S211 welding wire corresponds to the sphericity of the rich Fe phase in the joint weld,and the distribution along the weld seam and the steel boundary seam has formed an obvious one.The ri ch Fe band.The welded joint of S201 welding wire is composed of（γ+ε）two phase solid solution structure.The weld microstructure of S211 and S214 welding wires,except for（γ+ε+α）,and the alloy elements in the welding wire,Si,Al and the Fe in stainless steel respectively,produce the intermetallic compounds of Fe ₂Si and Fe₃Al.The tensile test,hardness measurement,electrical conductivity measurement and electrochemical corrosion of the copper and steel welded joints corresponding to three kinds of copper welding wires have been carried out.The results show that the copper steel joint obtained with different wires has a high tensile strength,and the average tensile strength is about 224MPa,reaching about 95%of the strength of the copper material and the tensile fracture.It is located in the copper side fusion zone;the micro hardness of the joint is generally declining from the steel side to the weld to the copper side,and the micro hardness distribution in the weld zone is uneven.This is mainly due to the melting of the stainless steel matrix in the welding process,which is mixed in the welding seam with the intense stirring of the arc force and the action of the molten pool flow.The molten pool is fast cold.The formation of irregular distribution of iron rich phase is caused by solidification,and the electrical conductivity of the three kinds of wire corresponding to the joint is in turn from high to low:S211>S214>S201,which is opposite to the electrical conductivity of the corresponding wire,indicating that adding Si and Al can improve the conductivity of the copper steel joint.There are two reasons:one is the reaction of Si,Al and Fe to produce Fe₂Si and Fe₃Al.The stable compound of-Fe reduces the increase of electron scattering caused by the lattice distortion caused by the solid solution element.Two is that Si and Al are ferrite forming elements,which will change some stainless steel matrix from austeniteγFe to ferriteαFe,and the crystal type changes,which indirectly reduces the formation of solid solution,to a certain extent.The electrical conductivity of the joint was improved.The polarization curves of the joints were measured by the electrochemical test in the mass fraction of 3.5%Na Cl solution.The corrosion potential and corrosion current density of the joint were obtained.The results showed that the corrosion resistance of the S214 joint was the best,the S201 joint was the second,and the S211 joint was the worst.Three copper welding wires corresponding to copper st eel joints were treated at different temperatures for 2h aging.Through the EDS analysis,it is found that the elements in the weld seam of the copper steel joint after annealing are homogeneous diffusion,the supersaturated solid solution in the weld is d ecomposed,and the Fe elements in the Cu matrix are precipitated to form the fine particles of the rich Fe phase,which is densely distributed in the weld seam,which causes the lattice distortion caused by the solute atoms.The decrease of electron scatte ring can improve the conductivity of the copper steel joint to some extent,but the tensile property of the copper steel joint decreases obviously after annealing,which is caused by the heat softening of the copper side after annealing.The corrosion potential of the copper steel joint increases after annealing,the corrosion of the joint increases,and the corrosion current density changes of the joint.Small,the corrosion rate is smaller.