Microstructure and properties of Cu-6wt% Ag composite thermomechanical-processed after directionally solidifying with magnetic field

High-field magnets require conductors made of Cu-Ag composites that have an exceptional combination of strength and electrical conductivity. Given that increase in strength is generally accompanied by decrease in electrical conductivity, researchers constantly seek the optimum balance between the two. In this paper, we reported the microstructure and properties of Cu-6wt % Ag alloy that had been directionally solidified under a magnetic field (MF) and thermomechanically processed. Thermoelectromagnetic convection by MF changed the mass transportation and diffusion of the melt, thus tilting the growth direction of proeutectic Cu dendrite toward the direction of the heat flow. Applying MF during solidification increased the primary dendrite arm spacing and the presence of supersaturated Ag in proeutectic Cu, but it decreased the volume fraction of the degenerated eutectic component distributed between the proeutectic Cu dendrites. The additional supersaturated Ag increased both the electrical resistivity and the hardness of the alloy. The increase in resistivity occurs because of increased impurity-scattering. The increase in hardness occurs as the result of solid solution strengthening. The precipitation temperature of Ag from Cu was between 275 degrees C and 325 degrees C, and the optimized temperature after aging was about 450 degrees C. After solidifying under MF, rolled Cu-6wt% Ag composite had a lower volume fraction of degenerated eutectic fibers. Thermomechanical processing at 300 degrees C promoted the precipitation of Ag out of the proeutectic Cu and simultaneously enhanced both the microhardness and the electrical conductivity of the alloy. (C) 2016 Elsevier B.V. All rights reserved.