Inhibition of Filiform Corrosion on AA6111-T4 Using In-Coating Phenylphosphonic Acid

Phenylphosphonic acid (H 2 PP) dissolved in a polyvinylbutyral coating is shown to profoundly inhibit filiform corrosion (FFC) on coated AA6111-T4. Following FFC initiation by application of aqueous HCl to a penetrative coating defect, the time-dependent extent of coating delamination was determined both optically and by repeated in situ measurements using a scanning Kelvin probe. FFC inhibition is shown to become almost complete when H 2 PP is ≥0.5% w/w. In-coating H 2 PP is also shown to depress Volta potential values associated with the intact (uncorroded) coated surface by up to 0.35 V.