Microstructure And Properties Of Heavily Deformed Cu-Ag-Fe Composite

Cu-Ag materials with high strength and high conductivity are widely used as winding coils in high-field pulsed(AC)and resistant(DC)magnets.The demand in the construction with higher strength magnets needs to further improve the strength and conductivity of the alloy.In this work,we replaced a portion of Ag with same volume fraction of Fe and investigated the influences of additional Fe on the microstructure of Cu-Ag-Fe alloy and the solubility of Fe and Ag in Cu matrix.The deformation and heat treatment were utilized to reveal the feasibility of Fe addition to improve the strength of Cu-Ag alloy.The experimental and theoretical results will be valuable for the optimization of Cu-Ag alloy.The conclusions are as follows:1)The as-cast microstructure of Cu-Ag alloy is refined with an addition of Fe element.The grain diameter of Cu-6%Ag(weight percent)alloy is ranged between 120μm and 220μm.An addition of 2wt%Fe refines the grain diameter of the alloy to be about 50μm.The spacing of Cu dendrite decreases from 28.5μm to 16μm after Ag is replaced with 0.5wt%Fe.With increasing Fe fraction,the morphology of Cu dendrites gradually transforms from dendrite to cellular crystalline structure,and the grain size becomes coarsening.Cu-4.6Fe alloy has a maximum grain of 66μm.The hardness of Cu-Ag-Fe alloy reaches to the maximum value of about 152.6HV with addition of about 2wt%Fe element.2)The fiber-like microstructure in Cu-Ag-Fe composites refines gradually with the increase in the deformation,and the replacement of Fe element promotes both Cu fibers and Ag fibers to be finer and shorter compared with Cu-6%Ag composite.Secondary Ag fibers formed during the drawing are mixed closely with the eutectic fibers.The fiber-like microstructure hardens Cu matrix,thus increasing the strength and hardness of composites gradually.Cu-Ag-2Fe has higher strength of 640MPa.At the drawing ratio of 5.3,the hardness and the electrical conductivity are 235HV and 38.5%IACS,respectively.3)In as-cast Cu-Ag-2Fe alloy,secondary y-Fe particles of 80-100nm are observed.The precipitation of y-Fe is coherent with Cu matrix.The precipitation hardens the hardness of the alloy.After heavy drawing,copper matrix in Cu-Ag-2Fe composite are drawn into a uniform ribbon fibers.A lot of secondary Ag fibers are found in Cu interface.After deformation,the precipitation of y-Fe becomes bcc a-Fe.A small part of the a-Fe are deformed to be fibrous.Most of a-Fe are slightly elongated.There are some of α-Fe to keep spherical structure.4)After homogenization treatment,the hardness of the alloy decreases slightly and the conductivity increases.After annealing treatment,the precipitate Fe from Cu matrix purifies Cu matrix,and decrease the impurity-scattering resistivity.This increases the electrical conductivity of the composite.However,the precipitate Fe is coarsened rapidly,and the hardness of the alloy decreases rapidly.After ageing treatment with 450℃ and holding 2h,the conductivity of the alloy is greatly improved,reaching 68%IACS,and the hardness value is 135HV.It is feasible to explain the Ag scheme with Fe replacement.