Research On The Forming Mechanism Of Copper/Steel Interface By Dip-Casting Composite

As a liquid-solid composite process,copper-steel dip-casting is a complex process that integrates diffusion,fusion,and Cu/Fe segregation and precipitation between steel and copper under high temperature.Especially the Cu diffusion and segregation in steel,which is the key to forming a good bonding layer between copper and steel.But as so far,there are a lot of work should be done,as the liquid-solid bonding mechanism between copper and steel,characteristics of liquid-solid interface,existence of Cu,Fe elements in transition layer,diffusion behavior of Cu in steel during liquid-solid bonding,as concerned in the liquid-solid bonding mechanism between copper and steel.For this reason,this study starts from the preparation of copper-steel dipping-casting composite materials,and conducts systematic research on the above problems,in order to provide theoretical support and technological guidance for the development of copper-steel composite materials prepared by dip-casting.The results of copper-steel dip-casting experiments and corresponding detection under different process conditions show that,a good metallurgical bonding layer could be formed by the copper-steel dip-casting.However,when the dip-casting temperature is low and the dip-casting time is short,it is not conducive to form the bonding between copper and steel by dip-casting;and if the dip-casting temperature is too high,it will increase the solidification defects of the casting-copper layer.In addition,with the increase of dipping temperature or the prolongation of dipping time,the Fe content in copper showed a gradually increasing trend,and the increase of Fe content did not control the conductivity and material cost of the whole material.For the characteristics of the copper-steel interface,the influence of the dip-casting temperature is relatively greater.When the dip-casting temperature does not exceed1125℃,the copper/steel interface is basically a straight line.Even if the dip-casting time is prolonged,the interface characteristics do not change much.And the scope of the new structure expands with the increase of the dipping temperature and the prolongation of the dipping time.With the increase of the dipping temperature,the corresponding positions of the maximum micro-hardness and Young’s modulus gradually shifted from the steel matrix side to the casting-copper layer side;and with the prolongation of the dip-casting time,the maximum micro-hardness and Young’s modulus increased gradually.The position corresponding to the maximum micro-hardness and the Young’s modulus also gradually transitions to the copper-steel interface,but does not exceed the interface area.The phase composition of the copper/steel interface has little relationship with the dip-casting temperature and dip-casting time,and is always dominated by single-phase FCC structure Cu and single-phase BCC structure Fe,accompanied by a small amount of Cu sulfide,Fe carbide and sulfide,as well as the Cu-Fe-S ternary phase,and there is no Cu-Fe binary phase.When the dip casting temperature is low,there is no new structure at the copper/steel interface,and the precipitated copper-rich phase is a typical unstable phase.The high-resolution results show that it is a coherent precipitate of BCC structures Fe and Cu,the crystal orientation is（110）,the precipitation of the copper-rich phase has a strengthening effect on the interface.When the dip casting temperature is higher,a large number of new structures appearing at the copper-steel interface are the concentrated precipitation products of the copper-rich phase,when the copper-rich phase precipitated in the liquid phase,it is relatively more stable.The high-resolution results show that,it is the co-precipitated of FCC-Cu andγ-Fe,the crystal orientation is（100）.Due to its relatively large size,it would not strengthen the interface as much as the small-sized precipitates at low temperature.The entire copper/steel interface area can be divided into four parts,the copper liquid area,the liquid-solid dynamic equilibrium area with relatively high Fe content,the copper/steel interface and the steel matrix area.For dip-casting composite technology,the formation of metallurgical bond between copper and steel is the result of both the fusion and diffusion mechanisms.For the diffusion of Cu in the interface and in the steel matrix,the diffusion coefficient of Cu in the steel increases gradually with the increase of the dip-casting temperature.When the dip-casting temperature increased from 1100℃to 1200℃,the diffusion coefficient of Cu in the steel matrix ranged from 8.52×10^-12cm²/s to 5.28×10^-10cm²/s,and the average diffusion activation energy was 103.24 k J/mol,which indicates that the diffusion efficiency of Cu is higher under the condition of liquid-solid composite.At the same time,the analysis results of the diffusion path of Cu in the steel matrix under different dip-casting temperature conditions show that when the dip-casting temperature is lower than 1150℃,the diffusion of Cu in the steel matrix is dominated by grain boundary diffusion;When the temperature continues to rise,the diffusion of Cu in the steel matrix gradually transforms into intragranular and grain boundary simultaneous diffusion.And at the same time,due to small contents,Mn,Si,P,C,S,and O elements have little effect on the diffusion of Cu at the interface and the steel matrix.To further analyze the structure of the copper-steel interface,a molecular dynamics model of Cu-Fe inter-diffusion was established in this study.The number density distribution and two-dimensional order analysis results of Cu and Fe atoms in the interface region show that,a certain local range of liquid-phase Cu atoms forms an ordered structure in the Cu/Fe interface region.The width of the ordered structure region,that is,the width of the liquid-solid dynamic equilibrium region,decreases with increasing temperature,and it is from 8（?）at 1100℃to less than 2（?）at 1200℃.It can be seen from the RDF curve results of different localities of the liquid-solid interface under different temperature conditions that,the Cu-Fe structure near the interface is basically an FCC configuration.And with the increase of temperature,the atomic stacking phenomenon in the Cu/Fe interface region gradually weakened.The stacking of atoms at the interface is determined by the configurations of Cu and Fe atoms.The consistent configuration of Cu and Fe atoms is beneficial to the diffusion of Cu atoms in Fe.For the diffusion mechanism of Cu atoms at the Cu/Fe interface,migration trajectories of some Cu atoms in the interface region under different temperature conditions has been tracked in this study,and had been counted.The results show that,the diffusion of Cu atoms in the interface region has two mechanisms:bound and adsorption-desorption.With the increase of temperature,the proportion of diffusion-bound mechanism atoms gradually decreased,indicating that high temperature will accelerate the migration of Cu atoms,making it easier to get rid of the confinement of the ordered structure region.At the same time,the calculation results of the diffusion coefficients of different regions in the liquid-solid interface show that,the three-dimensional diffusion coefficients of Cu and Fe atoms show a gradually increasing trend from the solid-phase Fe atom-dominant region to the liquid-phase Cu atom-dominant region.However,for the Z-direction diffusion coefficient,which is more critical for the diffusion and bonding of Cu and Fe,the Cu atoms show a gradually increasing trend,while the maximum value of Fe atoms appears at the boundary of the ordered layer,it indicates that the diffusion and dissolution of Fe atoms are mainly done in the boundary of ordered interface area.Considering the detection analysis results and molecular dynamics analysis results comprehensively,the best dip-casting process parameters for copper-steel has been determined,dipping temperature:1125～1150℃,dipping time:10～15 min.Figure 141;Table 13;Reference 158...