The effect of composition and thickness on the mechanism and kinetics of filiform corrosion occurring on zinc-aluminium-magnesium coated steel

Abstract The effect of coating thickness and composition on the kinetics of acetic acid-induced filiform corrosion (FFC) on Zinc-Aluminium-Magnesium (ZAM) coated steel is investigated. Scribe defects are created in organic coatings applied to ∼10 µm coatings of varying composition (1-6 wt.%. Al, 1-3 wt. % Mg), and fixed composition (Zn-1.5 wt. % Al- 1.5 wt.% Mg) but varying thickness (5-27 µm). FCC decreases with increasing Al (at fixed wt. % Mg) and thickness. A linear trend exists between thickness and iron exposure time. Findings are consistent with FFC advancing via a penetrative coating mechanism whereby exposed iron couples to the coating.