Identification of the Corrosion Mechanism of Brass-Coated Steel Wires in Cords Assembly

The corrosion behavior of brass-coated steel wire in cord assembly is discussed in this article. Experiments were performed on wires with different diameters and a cord composed of 19 wires. The open-circuit potential was recorded in a stagnant, aerated and neutral sulfate solution. Results showed a preferential initiation of the corrosion on morphological defects induced by the drawing. Moreover, the galvanic coupling between the brass layer and the steel led to the preferential dissolution of iron. For the cords, a crevice-like mechanism was identified. Inside the wire assembly, local acidification takes place because of the hydroxylation of iron ions. Lepidocrocite (γ-FeOOH) was detected by micro-Raman spectroscopy suggesting a pH of about 5 in the confined environment. At the external surface of the cord, both γ-FeOOH and Fe₃O₄ were identified. Their presence was attributed to the local variation of pH induced by a repartition of cathodic and anodic areas. Based on these results, a general scheme was proposed to illustrate the mechanism of corrosion of the cords.