On The Cu-6%Ag Filamentary Composite And Its Microalloying Of Rare Earth Elements

The Cu-6%Ag filamentary composite was prepared by cold drawing combined with intermediate heat treatments. The microstructure of the alloy at different working stage and the evolution of the filamentary structure were investigated.The as-cast alloy contains the Cu-rich matrix and Cu-Ag eutectic product with two-phase lamellar structure. During cold drawing, both phases rich-Cu and rich-Ag in the eutectic are elongated into fine filaments and the eutectic colonies change into bundles of filaments. There are also a lot of thin Ag precipitates in the form of fibers distributing in the Cu matrix. With increasing in draw ratio, the ultimate tensile strength increases while the electrical conductivity decreases for the alloy.The effects of rare earth elements on the microstructure and properties of the Cu-6%Ag were investigated. Adding minor rare earth elements to the Cu-6%Ag can refine the grains of Cu matrix and increase the interval of dendritic arms, the volume fraction of eutectic and the Ag concentration in both phases. The hardness and the strength of the alloy were enhanced due to the addition of rare earth elements.The effects of Cr and rare earth elements on the microstructure and properties of the Cu-6%Ag were also investigated. Adding l%Cr into the Cu-6%Ag make the eutectic structure more dispersal and reduce the Ag solubility in Cu matrix. Adding Cr element into the Cu-6%Ag can increase the strength and the electrical conductivity in the range of low draw ratio. Suitable microalloying of the rare earth elements in Cu-6%Ag-l%Cr alloy further improves the strength and hardly reduces the electrical conductivity.The influence of heat treatment after heavy cold drawing on the microstructure, mechanical and electrical properties of the Cu-Ag alloy was investigated. For the alloy annealed at 200 ℃, the morphology of two-phase fibers formed during cold drawing shows an insignificant change. The electrical conductivity slightly decreases while the hardnessand strength hardly change. For the alloy annealed above 400℃, the strength and hardness decrease and the electrical conductivity increases significantly. Moreover, the equiaxed grains, which change from the recrystallized filamentary structure, aligned along the wire axis can be observed in the microstructure. It is possible to obtain the expected combination of higher mechanical strength and better electrical conductivity for the alloy when the propagation of recrystal grains is limited inside the fibrous phases and the morphology of complete filamentary still kept down during annealing at suitable temperature.The ultimate tensile strength of 1.1 GPa and the electrical conductivity of 72%IACS in the composite were obtained by optimized preparation processes.