Effect Of Brazing Joint Clearance On Microstructure And Mechanical Properties Of Pure Copper Brazed 42CrMo Steel Joints

In this paper,pure copper is used as the brazing material to realize the brazing of the 42cmMo round steel with a diameter of 300mm,The braze gaps of the designed brazed joints were 0.03 mm,0.08 mm,0.10 mm,0.30 mm,0.50 mm,0.70 mm,0.90 mm,and 1.10 mm,respectively.After the welding is completed,the joints are subjected to microstructure characterization,mechanical property testing and fatigue testing,respectively.And compare the changes in the microstructure and properties of joints under different brazing gaps.The experimental results are as follows:(1)Observing the microstructure,the brazed joints with gaps of 0.08 mm,0.10 mm,0.30 mm,0.50 mm,0.70 mm,0.90 mm,and 1.10 mm were found to be very flat and beautiful,achieving a good quality connection.At the interface,it was found that the solder penetrated into the grain boundary of the base material.It is seen that the base material dissolves into the brazing material and is "island shape".As the gap of the brazing seam increases,the number of "islands" falling into the brazing material increases.(2)It was found from the EDS analysis that Fe in the base material was dissolved in the brazing material,and Cu in the brazing material was diffused to the base material.A small amount of migration has also occurred in the Cr element.(3)Joint tensile test shows:When the gap between the brazing seams is 0.10 mm,the tensile strength is the highest,reaching 728 MPa,which is 96.3%of the strength of the base metal.The tendency of the tensile strength to change with the gap is first increased and then decreased.(4)Joint impact test shows:The joint impact energy is the largest at 1.10mm clearance,with an average of 24.36J.The gap 0.10mm joint has the smallest impact energy,which is 8.49J.As the gap between the brazing joints increases,the impact toughness decreases first and then increases.(5)The joint bending test shows:When the brazing gap is 0.10 mm,the bending strength is the largest,which is 873 MPa.The trend of change with the gap is first increased,then decreased and then increased.(6)The microhardness results of the joints show:The hardness of the brazing joint is between 70-80HV.The hardness change with the weld gap is not obvious.The base metal has a high hardness of 252.68 HV,which is higher than the hardness at the brazing seam.(7)Fatigue test shows:As the weld gap increases,the number of fatigue cycles increases first and then decreases.The joint has a maximum number of fatigue cycles of 0.10 mm.Fatigue fractures occur at the weld.The fatigue S-N curve of the joint with a gap of 0.70 mm was drawn,and the fatigue strength was 203.06 MPa,which was higher than the tensile strength of pure copper.(8)It was found from the mechanical property test that the fracture of the joint occurred in the middle of the pure copper brazing joint,and no fracture occurred at the interface between the brazing material and the base metal.