Investigation On The Microstructure And Properties Of Friction Welded Joints Between Copper And 45 Steel

In recent years,with the rapid development of science and technology and the rapid development of economy,industrial production has new requirements for new materials and technological methods.The demand for dissimilar materials bonding technology arises at the historic moment,and the research on dissimilar materials bonding technology has attracted more and more attention.In this paper,five groups of technological parameters of different forging pressure are used to connect the dissimilar metal continuous driven friction welding of T2 copper and 45 steel.The microstructure of welded joints of copper/45 steel was observed and analyzed by metallographic microscope and scanning electron microscope.At the same time,the mechanical properties of welded joints were analyzed and compared by tensile test and microhardness test.The microstructure evolution mechanism and mechanical behavior of welded joints under different top forging forces were studied and the optimum welding process parameters were determined.First of all,under the established technological parameters of the spindle speed of 3000 r/min,the friction time of 14 s,the first friction pressure of 390 MPa and the second stage of friction pressure of 975 MPa,the test range of the top forging pressure is divided into five groups,155 MPa,175 MPa,195 MPa,215 MPa,235 MPa,respectively.The friction welding experiments were carried out under five groups of forging pressure,and the main results were as follows:The effect of top forging force on the microstructure of friction welded joints of copper/45 steel was studied.Under five groups of forging pressure,the macroscopic appearance of the whole welded joint shows the phenomenon of copper clad steel,the plastic deformation appears on the side of red copper,and the flying edge quantity increases with the rising of the pressure of the top forging.Through the observation of the microstructure of welded joints,the results show that the microstructure of 45 steel has little change under different forging pressure,and does not show obvious difference with the change of forging pressure,and the microstructure of heat-affected zone is formed by fine recrystallization zone.The coarse incomplete recrystallization region is formed with a small amount of Weissner body structure.Dynamic recrystallization takes place in the copper side near the weld,forming fine equiaxed grains,and the grain coarsening zone is located in the far weld.In the radial direction,the grain size at the center of the circle is obviously larger than the radius of the center at 2/3,and with the increase of forging pressure,the grain size of the copper side heat affected zone was also refined.The results of line scanning show that the bonding of the weld is accomplished by the interdiffusion between the Cu and Fe atoms,the bonding strength of the interface is high,there is no intermetallic compound,and in the fixed range of forging pressure,with the increase of the forging pressure,The diffusion zone of the weld is widened with mechanical mixing,and the shape of the weld is changed from a straight line to a curve.The effect of top forging force on tensile properties of friction welded joints of copper/45 steel was studied.The tensile curve of the welded joint first increased and then decreased slightly.When the forging pressure was 215 MPa,the maximum tensile strength was 285 MPA and the base metal strength was reached.The fracture mode of the welded joint was ductile fracture.Then the notched test was carried out on the welded specimen with the pressure of 215 MPa,and the distribution of strength in radial direction was analyzed.The results show that the tensile strength increases first and then decreases with the increase of diameter,and when the center radius is 4~6mm,the bonding strength of welded joint is the best,that is,the tensile strength of welded joint along radial distribution is the best at about 2/3.The effect of top forging force on the microhardness and corrosion resistance of friction welded joints of copper/45 steel was studied.The axial micro hardness analysis of five groups of welded joints under different pressure shows that the influence of the top forging force on the micro hardness in the axial direction is not obvious,and the five groups of parameters show the same trend.That is,the micro hardness of welded joints is higher than that of copper and less than 45 steel,which is between the two.For the welded joints with upsetting pressure of 215 MPa,the micro hardness of the welded joints is detected along the radius.It is found that the minimum hardness value is 141.7 Hv at the weld,and the highest hardness is at 2/3 of the center radius,reaching 210.3 Hv.The electrochemical test results show that the corrosion resistance of the welded joint increases with the increase of the forging pressure and there is no obvious welding defect in the whole welded joint.