Self-healing processes in coil-coated cladding studied by the scanning vibrating electrode

The ability of the zinc layer in coil-coated cladding to protect the underlying metal substrate exposed to the environment through a sub-centimeter circular defect was established by using the scanning vibrating electrode technique (SVET). The onset of electrochemical corrosion is observed through the development of local anodes and cathodes in the defective system, with the formation of soluble zinc species. The dissolution process is maintained until a sufficiently high concentration is attained by the metal ions, and their subsequent precipitation inside the holiday blocks the defect as to hinder further corrosion. A self-healing effect was thus observed. The role of zinc salts was confirmed by SEM and EDX observations.