Investigation On Microstructures And Mechanical Properties Of Copper-Iron-Copper Composite-Structure Components Manufactured By Plasma Arc Cladding Process

For solving the problems that pure copper sticks to rifling and the pure iron rotating band scrapes rifling,a new "copper-iron-copper" composite rotating band was designed.Then the dissimilar double-wire plasma arc cladding process was used to carry out the cladding process experiments of composite rotating band.The interface behavior,microstructure,the change of composition,hardness distribution and shear performance of the copper-iron-copper composite joints were investigated.The research supports the development of rotating band welding technology and the study of welding mechanism between copper and steel.First of all,the single-pass plasma arc cladding process experiments of pure iron were conducted.And the single-layer and multi-pass cladding process experiments of pure copper and soft iron were carried out respectively.Then the process parameters of single-layer and multi-pass cladding of pure iron and pure copper were obtained.Moreover the structures of "copper-iron-copper" composite rotating band were designed,and their cladding paths were planned.The copper-iron-copper composite cladding process test on steel plate was carried out,and the obtained process parameters provided process basis for composite rotating band cladding.According to the process parameters,the multi-layer and multi-band plasma arc cladding process of copper-iron-copper composite rotating band was designed and implemented.Each layer of pure iron was cladded by same process parameters to ensure the tiny penetration depth of cladding pure iron and the reliable combination between pure iron layers.The pure copper base layer was cladded with constant welding current to ensure that there was no penetration near the pure copper-steel interface.And the pure copper coating layers were cladded by the process of current decreased with the change of cladding position to avoid the dent of the pure copper coating layers.The cladding of composite rotating band with good appearance was realized.Through the observation of the axial and circumferential sections of the copper-iron-copper composite rotating band,it was found that the bonding state among the layers and passes of pure iron is in good condition,and the same is ture for pure copper cladding layers.The pure iron and pure copper cladding layers are free of any lack of fusion.The analysis of the microstructure of the composite joint shows that the interface between pure copper and steel at different positions of the rotating band is clear,and there is no pan-iron in pure copper base layer and copper infiltrated in steel.Moreover,there is no obvious transition layer at the pure copper-iron interface.The penetration depth of soft iron cladding is about 0.5mm.In addition,part of the pan-iron near the interface between pure copper and pure iron diffuses into the pure copper coating layers in the current slow decreasing region,while the interface between pure copper and pure iron in the current constant region is straight without diffusion of pan-iron.The EDS analyses were conducted on the copper-iron-copper composite joint.The results show that there is an element diffusion zone with width less than 20?m in the pure copper-steel interface at different positions of rotating band,which indicates that the metallurgical combination between pure copper band and steel substrate is achieved,and there is no pan-iron and copper infiltration.The iron content of copper cladding layers is less than 2%.At the interface of soft iron and steel,there is also an element diffusion zone with a width of no more than 20?m,which indicates that the composition transition of steel in the soft iron cladding area is less.The results of hardness test of copper-iron-copper composite rotating band indicate that the microhardness of the rotating band from the steel to the pure copper band drops from above 180 HV to below 100 HV in different positions of rotating band,showing that the fusion zone at the pure copper-steel interface is very narrow in the whole rotating band,there is no transition zone,there is no pan-iron in the pure copper layer near the pure copper-steel interface,and there is no copper infiltrated in steel.The average microhardness of pure iron band is about 120 HV,which is significantly less than that of steel substrate.And the average microhardness of pure copper band is about 85 HV.The shear test results show that the shear process of the composite rotating band consists of the shear stage of the hardfacing layer of pure copper band and the shear stage of the iron-copper composite band.There is a obvious step in the shear force-displacement curve.The shear strength of the composite rotating band is over 170 MPa,and the shear strength satisfy the positive correlation with the width of the pure iron base layer.All shear specimen fractured in the composite rotating band,which shows that the bond strength between the composite rotating band and the steel substrate is higher than the shear strength of the rotating band itself.