Development of High-Strength, High-Conductive Copper-Silver Alloys

Abstract

Development of highly conductive materials with high strength is requisite for conductors of high field magnets. To develop such materials, the Cu-Ag alloys (2-60 at%Ag) and their fabrication methods have been investigated. This paper describes the mechanical and electrical properties as well as the microstructure of the drawn wires of the alloys, as functions of Ag concentration and reduction in cross-sectional area (RA), and furthermore the heat-treatment effects on those properties.The Cu-Ag alloys were prepared by melting electrolytic Cu and pure Ag pellets in an argon atmosphere, and then cold-drawn to a 99.2%RA. The heat treatments were performed several times during the drawing process. The alloys consist of two phases, i. e. Cu solid solution (α-phase) and Ag solid solution (β-phase). These two phases can be drawn down to fine fibers below μm in diameter. The relationship between the tensile strength and the fiber diameter follows the Hall-Petch formula. The optimum combination of the high strength and the high electrical conductivity were obtained, by cold-drawing the alloy with intermediate heat treatments at 350-450°C for 1-2 h. On the other hand, heat treatments prior to the drawing process scarcely influence on those properties. The heat-treated Cu-16 at%Ag composite of 99%RA showed the ultimate tensile strength of 1000 MPa and the electrical conductivity of 80%IACS, at room temperature.Since the Cu-Ag alloys fabricated by the present method have higher values of both tensile strength and conductivity than those of Cu-Nb and other Cu-based alloys, they would become the most promising conductor materials for the high field magnets.