Study On The Cu-12%Ag Filamentary Composite And Effects Of Rare Earth Elements Alloying

Cu-12%Ag filamentary composites were prepared by cold drawing combined and intermediate heat treatments. The ultimate tensile strength of 1 .02GPa with the electrical conductivity of 78%IACS in the wires was achieved with optimized preparation processes. The microstructure of the alloy at different working stage and the evolvement of the filaments were investigated. The as-cast alloy contains with both structures Cu-rich matrix and Cu-Ag eutectic. The eutectic consists of two-phase mixture of lamellar structure. During the cold drawing, both phases in the eutectic are elongated into fine filaments and the eutectic changes into the filament bundles. There are also a lot of thin Ag precipitates in the form of filaments distributing in the Cu matrix. With increasing draw ratio, the ultimate tensile strength increases while the electrical conductivity decreases for the alloy.The influence of rare earth elements on the microstructure and properties of the Cu-12%Ag was investigated. The morphology of the Cu dendrites and the Ag solubility in Cu phase were changed by adding rare earth elements. The grain size slightly decreased with increasing the content of rare earth elements. Suitable microalloying of rare earth elements in the alloy Cu-12%Ag can improve the conductivity. However, the conductivity decreases with increasing rare earth addition when the content of rare earth is higher than 0.1%. The hardness of the alloy enhances and the strength hardly changes with the addition of rare earth elemrnts.The influence of heat treatment after heavy cold drawing on the microstructure, mechanical and electrical properties of the alloy was investigated. For the alloy annealed at 200℃, the morphology of double-phase fibers formed during cold drawing shows an insignificant change but ultimate tensile strength slightly decreases, while hardness and conductivity slightly increase. For the alloy annealed above 400 ℃, the strength and hardness decrease and conductivity increases significantly. Moreover, the equiaxed grains aligned along the wire axis can be observed in the microstructure instead of filamentary morphology. It is possible to obtain the expected combination of better strength and conductivity for the alloy when the propagation of recrystallized grains is limited insidethe fibrous phases and the morphology of complete filamentary still kept down during annealing at suitable temperature.The influence of heat treatment on the microstructure, mechanical and electrical properties of the Cu-12%Ag alloys contained with rare earth elements was also investigated. After annealing at low temperature, the addition of rare earth elements has few effects on the evolution of microstructure and properties. After annealing at high temperature, the addition of rare earth elements refines the rycrystallization grains and improves the precipitation of Ag. The alloy containing rare earth elements possesses higher strength but lower conductivity after annealing at higher temperature than that free of rare earth elements.