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 120?m and 220?m.An addition of 2wt%Fe refines the grain diameter of the alloy to be about 50?m.The spacing of Cu dendrite decreases from 28.5?m to 16?m 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 66?m.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 ?-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.