Study On Microstructure And Mechanical Properties Of MIG Welding Joint Between Red Copper T2 And Q235 Steel

With the bigger difference of dissimilar material in composition,organization and properties,weldability of dissimilar materials becomes worse.In the industrial production,we often encounter welding of red copper T2 and steel Q235,the melting point of red copper T2 is 1083℃lower than that of steel Q235 about 400℃,thermal conductivity of red copper T2 is 7-11 times higher than that of steel Q235,so it is a great difficulty to weld them.In this paper,using HS201 as the filler metal 20mm thick red copper T2 plate and steel Q235 plate were welded by MIG welding method.The composition,microstructure and properties of welded joints were studied and we draw the following main conclusions:(1)Analysis results of microscopic microstructures and composition show that the weld seam is made of coarse crystal grains,and the grains in the heat affected zone of copper side are coarse,and grain refinement occurs in the heat affected zone of steel side.The scanning results show that the average mass fraction of Fe in the weld seam is 5.02%and the atomic percentage is 5.65%on average,Fe in the base metal of low carbon steel is diluted into the weld seam and the metal in the weld seam is alloyed.The results of line scanning show that the mutual diffusion of Cu and Fe is found in the fusion zone of steel side.The surface scanning results show that elements are uniformly distributed.(2)The mechanical test results show that the tensile strength of the welded joints is 214.62Mpa,the tensile strength of red copper is 235.73 MPa and the final fracture is in HAZ of copper side;the impact energy of Q235,HAZ of steel side,weld seam,HAZ of copper side and T2 are 104.5 J,220.8 J,116.5 J,111.8 J,113.7 J;after bending tests of 90 degrees,no crack is found in the welded joints,the flexural strength reaches 1052MPa;the specimens break in HAZ of copper under shear stress in the torsional test,the torsional strength reaches 558.3 MPa.(3)Although the weld seam is defective,the fatigue specimens still break in HAZ of copper side and their fatigue limit reaches 71 MPa,which can meet the actual needs.Fatigue fractures of the specimens show that the fatigue crack mainly originates from the surface of the specimens,fatigue arcs and fatigue strips form in the process of crack propagation.The specimens fail when cracks extend to the critical size.(4)According to JB/T4730.2-2005 results of X-ray detection on the welding seam are up to Ⅱ level.