Electrochemical Characterisation of Filiform Corrosion on Aluminium Rolled Products

When aluminium is protected by an organic coating a special form of corrosion can occur underneath the organic coating; filiform corrosion. This form of corrosion manifests itself as threadlike filaments under the coating, it causes local delamination of the coating and the coating cannot protect the substrate anymore. The properties of the aluminium substrate have a strong influence on the filiform corrosion properties of the end product. It is in the interest of the aluminium producers to understand how the composition and the microstructure of the substrate influence the filiform corrosion properties. There are two mechanisms that can explain filiform corrosion. These are the presence of a surface layer with an extreme low potential and the presence of a large amount of cathodic intermetallics