Effect Of Pure Copper Brazing Thickness On Microstructure And Mechanical Properties Of 42CrMo Steel And Q235 Steel Brazed Joint

In order to explore the influence of the gap between the brazing joints on the microstructure and mechanical properties of the welded joint,0.15 mm,0.3 mm,0.5 mm,0.7mm,1.0 mm,1.3 mm,6 sets of brazing joints with different thicknesses were selected.42CrMo round steel is used as the base material,and TU1Cu is used as the brazing material for large-area docking in the brazing furnace.The microstructure and composition analysis of 6 groups of joints with different thicknesses of solder joints were performed under OM,SEM and EDS;mechanical tests such as tensile,impact,bending,microhardness and high cycle fatigue were performed at room temperature,and the results were analyzed.Come to the following conclusions:(1)Observing the microstructure of the weld seam,it is found that Tensile specimens with brazing gaps of 0.15 mm,0.3 mm,0.5 mm,and 0.7 mm were all broken at the base material with a maximum strength of 479 MPa,is 2.77 times the tensile strength of the Cu,Tensile specimens with a gap of 1.0 mm and 1.3 mm were broken in the weld.The tensile strength was up to 465 MPa,which was 2.69 times the tensile strength of copper,And the tensile strength decreases as the gap between the joints increases.The maximum impact energy of the specimen with a gap of 1.3 mm is 22.5 J;the bending strength decreases first and then increases with the thickness of the joint,and the maximum is 845 MPa.The hardness of the base metal on the 2CrMo side is higher than that on the Q235 side.The Cu hardness in the weld is between 70 and 80 HV,However,the hardness is slightly higher than that before welding(65 HV),and the hardness at the interface is between the base metal and the weld.(2)Through mechanical experiments at room temperature,the following conclusions can be drawn:tensile samples with gaps of 0.15 mm,0.3 mm,0.5 mm,and 0.7 mm at the gap are all broken at the base material.Tensile specimens with a tensile strength of 2.77 times and a gap of 1.0 mm and 1.3 mm at the weld seam were broken at the weld.The maximum strength was 465MPa,which was 2.69 times the tensile strength of copper.The impact specimens all fracture at the weld,and the impact toughness of the welded joint increases with the increase in the gap between the welds.The impact energy of the specimen with a gap of 1.3 mm is up to 22.5 J;The strength decreases first and then increases with the thickness of the solder joint.The maximum is 845 MPa.The hardness of the base metal on the 42CrMo side is higher than that on the Q235 side.Slightly increased,the hardness at the interface is between the base metal and the weld.(3)Two-stage high-cycle fatigue experiments were performed on 6 groups of samples with a thickness of the weld.It was found that the samples with a cycle number of less than 107 fractures at a stress amplitude of 200 MPa were all broken at the weld.The crack gap increases and decreases;the number of fracture cycles of a joint with a gap of 0.5 mm at different stress amplitudes decreases with increasing stress.(4)Through the fracture analysis of tensile,impact and fatigue test fracture samples,it is found that the fracture of the tensile sample fractured at the base material has a cup cone shape,the fiber area is covered with tough dimples,and the tensile test at the weld seam is broken.The fracture of the sample is relatively flat and covered with dimples;the fracture of the impact specimen is covered with dimples and the dimples have a certain direction;the fatigue source,the expansion zone and the transient fracture zone can be clearly observed in the fracture specimen fracture.