Microstructure evolution and mechanical properties of high strength and high conductivity Cu Fe alloy wire prepared by cold drawing

CuFe alloy wire is widely used in the field of electronic information because of its high strength and high conductivity. In this study, Cu-5Fe-0.1Si-0.3 Mg-0.05RE (La, Ce) alloys were prepared by cold drawing and heat treatment. The microstructure evolution of the alloy during deformation was studied by optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). Three kinds of second phases with different sizes and shapes were successfully constructed in the designed alloys, including fibrous iron phase, submicron spherical iron phase and nano spherical phase. The strength of the alloy is greatly improved by drawing deformation, with only slight reduction of the conductivity. Through joint addition of Mg, Si and rare earth elements, the designed CuFe alloy wire rod has excellent overall properties. It's electrical conductivity, tensile strength, yield strength and elongation reached 63.8% IACS, 831 MPa, 730 MPa and 6.1%, respectively. Detailed characterizations of the alloys reveal that: the addition of Mg reduces solid solubility limit of iron in matrix and spaces between iron phases; the FeSi phase formed by Si and Fe promotes the precipitation of iron phase; and the addition of rare earth inhibits segregation of second phase, recovery and recrystallization of the alloy, and the coarsening of Fe phase. The mechanical properties of the alloy are improved by fiber strengthening, Hall-Petch strengthening and precipitation strengthening, respectively. The contributions of precipitation strengthening, fiber strengthening and Hall-Petch strengthening to yield strength are 65 MPa, 59 MPa and 277 MPa, respectively. The microstructure of dislocation and fibrosis is the main factor of alloy strengthening.