Critical Factors in the Inhibition of Filiform Corrosion by in-Coating Ion-Exchange Pigments

Abstract

In-coating cation and anion exchange pigments are studied with respect to their ability to inhibit filiform corrosion (FFC) on AA2024 aluminium alloy substrates. Smart-release cerium (III) and yttrium (III)-exchanged bentonite pigments are shown to be largely ineffective in reducing rates of FFC propagation. The reasons for this are discussed in terms of the chemistry of the filiform localised corrosion cell. In contrast, anion-exchange hydrotalcite based pigments are highly effective inhibitors of FFC. The efficiency is greatly improved by exchanging the native carbonate ions with anionic species which act as complexing agents for copper ions. The implication of these findings with respect to the mechanism of FFC on copper containing aluminium alloys is considered.