Research On The Regulation Mechanism Of Nano-precipitation And Properties In Cu-Ag-Fe Alloy With High Ag Content

Cu-Ag alloy is one of important candidates for the winding conductors used in the construction of high-field magnts because of its superior combination of strength and electrical conductivity.With increasing requirements of high-field magnets,the improvement of properties in Cu-Ag alloy is becoming much more crucial.The regulation of nano-sized precipitates in Cu-Ag alloy is one of key factors for the optimization of properties.On the basis of the investitation of the precipitation behaviors of nano-sized Cu precipitates in as-solid-solution and as-cold-rolled Ag-7%Cu supersaturated solid-solution alloy,in this study,Cu-Ag alloy with high Ag contents,which are one of popular chemical components in winding conductors,is selected as a representative alloy.The alloying of minor Fe,thermalmechanical deformation and the imposition of 12 T high magnetic field(HMF)were subjected to the processing of Cu-26%Ag alloy in order to regulate the multiscale microstructure.The precipitation mechanisum of nano-sized co-precipitates of Ag-rich,Cu-rich and Fe-rich precipitates and interaction between the nano-sized co-precipitates were specifically studied.The influence of multiscale microstructure on the strength and electrical conductivity of Cu-Ag-Fe alloy was clarified.The strengthening mechanism and conductive mechanism of alloy were also explored.The study will provide the scientific knowledge for the R&D of Cu-Ag-Fe alloy.The precipitation kinetics of as-solid-solution and deformed Ag-7%Cu alloys demonstrated that the temperature of Cu-rich precipitates precipitated out of Ag matrix was ranged from 300? to 350? and the activation energy of Cu precipitates was 111±1.6 kJ/mol.Because of the presence of deformation energy,the activation energy of Cu precipitates of cold-rolled Ag-7%Cu alloy was increased to 128±12 kJ/mol,where the precipitation kinetics provided the useful information for the proper precipitation temperatures by aging.The morphology of Cu precipitates in as-solid-solution and as-rolled Ag-7%Cu alloy was compared and found relatively big spherical nanoparticles with size less than 100 nm and relatively small nanoparticles with size less than 10 nm.The conductive mechanism and strengthening mechanism of Ag-7wt%Cu alloy indicated that the Cu precipitates played dominate roles on the electrical resistivity of as-solid-solution and as-cold-rolled Ag-7%Cu alloy,and dislocation and deformation twinning were significant to the hardness.Solid-solution treatments and ageing heat treatments were employed to investigate the precipitation behaviors of nano-sized Ag,Cu and Fe precipitates and the effect of precipitates on the properties in Cu-Ag-Fe alloy new system based on the Cu-26%Ag with minor Fe addtion.The results from precipitation kinetics of as-solid-solution and deformed alloy indicated that the activation energy of Ag precipitated out of Cu matrix and the activation energy of Cu precipitated out of Ag matrix were 66.4±6.4 kJ/mol and 125±13.8 kJ/mol respectively in the Cu-26%alloy.With respect to the Cu-25%-0.1%Fe alloy,these two energies were 63.5±3.2 kJ/mol and 129±8.9 kJ/mol,respectively.The Cu-25%Ag-0.1%Fe alloy consisted of continuous rod-shaped Ag precipitates as well as nano-sized distributed uniformly Fe precipitates after ageing heat treatments.The Fe addition decreased the size of continuous rod-shaped Ag precipitates.The presence of Fe precipitates increased the ultimate tensile strength(UTS)by 8%.Different thermal-mechanical processings were applied to investigate the evolution of deformed microstructure and resulting properties.The nano-sized microstructures such as eutectic fibers,fibrous Ag precipitates,dislocation cells and deformed twins were formed in thermal-mechanically deformed Cu-Ag-Fe alloys.The Fe addition refined the size of eutectic fibers and fibrous Ag precipitates,increasing the UTS.The UTS of Cu-25%Ag-0.1%Fe was 8.8%higher than that of Cu-26%Ag alloy at strain 7.4.Appling intermediate heat treatment promoted the precipitation of Ag and Fe out of Cu matrix,and decreased the electrical resistivity by reducing the impurity scattering from the supersaturated Ag and Fe in Cu matrix.The UTS of Cu-25%Ag-0.1%Fe alloy with a deformation strain of 7.4 was 768 MPa,and the electrical conductivity was 78.4%IACS after subjecting ageing at 450? for 2h,which was comparable with the properties of Cu-Ag alloy treated with similar process.An external 12-T HMF was imposed to different solidification process of Cu-26%Ag,Cu-25%Ag-0.1%Fe and Cu-24%Ag-1%Fe alloys.Both the application of HMF and the addition of Fe reduced the lamella spacing of eutectics and the average size of Ag precipitates.The introduction of HMF promoted the precipitation of Fe out of Cu matrix,forming nano-sized Fe precipitates dispersed uniformly in Cu matrix.The morphology of Fe precipitates was almost unchanged during cold rolling process.The formation of a large number of nano-sized interfaces between Ag fibers and Fe precipitates with Cu matrix remarkably enhanced the strength of alloys.The strength and electrical resistivity of Cu-25%Ag-0.1%Fe and Cu-24%Ag-1%Fe alloys solidified with holding at 760? after cold rolling were higher than that of alloys solidified with holding at 450? after cold rolling.