Research On Plastic Deformation Characteristics And Conductivity Mechanism Of Cu-Ag Composite Wires With High Strength And High Conductivity

The pulsed strong magnetic field is an imporant extreme-experimental platform in modern scientific rescarch.The conductor materials with high strength and high conduclivity are regarded as the key hardware to realizc a strong pulsed magnetic field.Normally.conductor maerials were required to be sble to withstand the huge Lorentz force generated by the magnet coil.transport a huge current,and meet the requirements for those extreme service environments.Among many conductor maierials,the Cu matrix composites Cu-X(Ag,Nb,Cr,Fe)are conduced as the most poicntial material.Compared with other copper-based materials,Cu-Ag material has good conductivity due to the addition of Ag,and its excellent plastic deformation ability enables it to obtain high strength while maintaining good electrical transport propcrties throuth copper matrix.Although the research work of Cu-Ag wire has been carried out fur many years.the typical incompatible mechanical and electrical propenties has not been improved,studies show that the decreaing conductivity commonly rises with increased strength due to the boosting of the defect density at grain boundary or interface,which seriously limited the application of Cu-Ag wire.This work focused on the optimization the process on the comprchensive properties plastic deformation of Cu-Ag multi-filamcntary composite wires.Through the different deformation procedures and heat trcatments,the mierostructure and the microtexture evoltution and their corresponding influence to mechanical and electrical properties were thoroughly studied to provide theoretical suppot and experimental guidance for the preparation of high-performance conductor materials.The restarch results are as follows;(1)Cu-Ag multi-filamentary composite wire with Ag nano filaments wire was obtained by melting method combined with cluster drawing technology,followed by drawing and rolling at room temperature respectively.The influence of shear band,dislocation,twin and precipitation on the strengthening mechanism and conductive mechanism of wires were analyzed.Firstly,the appearance of shear bands in the rolling process indicated the occurrence of inhomogeneous deformation,at the same time the hardness on the cr-oss section and longitudinal section of the wire showed significant anisotropy.The reduction of tensile strength as the rolling reduction exceeded 57.0%was considered to result from the texture transformation from Copper to Brass through the texture components analysis methods and Schmid factor methods.On the other hand,during the drawing,the proportion of the phase interface increased with the decrease in wire diameter,and the number of eutectic fiber bundles and dislocation density played a leading role in affecting the wire properties.As the strengthening effect of eutectic fiber bundle and dislocation become prominent,the tensile strength was significantly enhanced whereas the conductivity decreased due to the serious interface scattering and dislocation scattering.(2)On the basis of the drawn wire with excellent properties obtained above,the intermediate annealing treatment and the final annealing treatment were conducted to eliminate work hardening and improve the conductivity.And researched the evolution of the microstructure of the wires,revealed the law of its influence on the strength and conductivity of the wires.After the wires were annealing at different temperatures,Ag precipitates were precipitated in the structure at 260℃.As the temperature continuing to rise,recovery and recrystallization soften the material.At the same time,the filaments were coarsened,spheroidized,cracked,and the interface scattering was weakened.The conductivity was increased while the mechanical properties was reduced.The strength and conductivity of the wires at 260℃ reached a comprehensive match.On the other hand,by comparing different aging time and aging temperature,it was found that the extension of aging time has less influence on the core wire coarsening and cracking degree.In order to further study the effect of microstructure changes on material properties after intermediate high temperature annealing of wires,the multi-filamentary composite wires were annealed at 745℃.The grain boundary segregation occurred,along with the needle-like structure at the high temperature.As the drawing proceeds,the radial force promotes the recombination of wires,leading to the organization to its original state,the strength still conformed to the size effect,showed the smaller the wires diameter,the higher the tensile strength.(3)When the composite wires were rolled and drawn at low temperature,the Cu-Ag wires with low stacking fault energy can maximally inhibit dislocation to cross slip,climb and activate twinning deformation,making the wires easier to conduct plastic deformation and make the wires more plastic deformation.Compared to room temperature rolling,there was no shear band under low temperature rolling,and the strength of wires decreased due to the unstable propagation of cracks at the later stage of deformation.After the wires were drawn at low temperature,the wires were refined significantly,the dislocation density increased,and the mechanical properties of the material are improved due to the interface strengthening and twin strengthening.In addition,more Ag phase is precipitated during low-temperature deformation,which reduced the solid solution scattering and improved the conductivity.By adjusting the deformation and annealing process,the best match of wire conductivity and strength was obtained,reached 997 MPa and 82.6% IACS respectively.