Microstructures and Mechanical Properties of Highly Electrically Conductive Cu–0.5, Cu–1 and Cu–2 at%Zr Alloy Wires

Abstract

Hypoeutectic Cu–Zr binary alloys have originally been studied in order to develop wires with both high strengths and high electrical conductivities. This study aimed to improve the electrical conductivities of Cu–0.5, Cu–1 and Cu–2 at% Zr alloys, which have Zr contents lower than those of high-strength Cu–3, Cu–4 and Cu–5 at% Zr alloys. Cast rod samples, whose lengths and diameters were 180 and 12 mm, respectively, were prepared by copper-mold casting and wire-drawn to diameters in the range of 1–0.031 mm (drawing ratio, η = 4.8–11.1). The microstructures and mechanical properties of the obtained wires were investigated and compared to those of Cu–3, Cu–4 and Cu–5 at%Zr alloy wires that had been investigated in a previous study.
The eutectic phases found in the cast rods consisted of α-Cu primary phases and phases of the intermetallic compound Cu₅Zr. The eutectic phases became isolated, like small islands, in the matrices, and their volume fractions decreased with a decrease in the Zr content. The orientations of the α-Cu and Cu₅Zr phases around the boundaries of these eutectic phases were similar. After the wiredrawing process, the intermetallic compound in the eutectic phases transformed into Cu₉Zr₂ in the case of the Cu–0.5 at%Zr alloy and into Cu₈Zr₃ in the case of the Cu–1 at%Zr alloy. The electrical conductivity (EC) and ultimate tensile strength (UTS) values of the alloys depended on the volume fractions of their eutectic phases. However, the changes in these properties with the change in the drawing ratio were smaller than those in the case of the high-strength Cu–3, Cu–4 and Cu5 at%Zr alloy wires. The EC and UTS values of the Cu–0.5, Cu–1 and Cu–2 at%Zr alloy wires drawn at values of η greater than 8.0 were 61–83% IACS (International Annealed Copper Standard) and 690–1010 MPa, respectively. When combined together, wires of the resulting hypoeutectic Cu–Zr binary alloy exhibited EC and UTS values of 16–83% IACS and 690–2234 MPa, respectively. These results showed that instead of there being a tradeoff between these properties, the values of both these properties increased at the same time.