Influence of impurities in cathodic copper on the ductility of copper wires

The main characteristic of cathodic copper is its concentration of impurities because this determines the mechanical properties, i.e., ductility, of the derived copper wires. However, the results of standard mechanical tests to evaluate ductility show that there is no clear correlation between the content of impurities in the cathodes and the ductility of the copper wires. In this study, from traction tests on copper wires and observation of their fracture surfaces by means of scanning electron microscopy and energy dispersive spectroscopy, it has been concluded that the principal impurity affecting the ductility of the copper wires is oxygen, which is mainly incorporated during the melting of the cathodes and casting of the rods. In addition, to discriminate the effect of oxygen concentration in copper ductility, the used probes or wires must have the same previous deformation and must not have been annealed. When copper wires are annealed, cuprous oxide particles are also more dispersed in the matrix, and not only segregated and concentrated as occurs in the non-annealed condition, thus diminishing the mechanical fragility effect of the oxide.