Time-lapse potentiometric imaging of active filiform corrosion using a scanning Kelvin probe technique

The kinetics and mechanism of filiform corrosion occurring on polymer coated AA2024-T3 aluminium alloy are investigated using a scanning Kelvin probe technique (SKPT). Repeated scanning by SKPT is used to generate a time-lapse animation showing the dynamic evolution of localised free corrosion potential (E corr ) patterns. E corr values in the head region of propagating filaments are up to 150 mV lower that the intact polymer coated surface, indicating local depassivation. However, E corr values in the filament tail are ca. 100 mV higher than background, indicating superpassivation. Spatial analysis of instantaneous E corr distributions indicates that anodic metal dissolution is concentrated at the leading edge, and cathodic oxygen reduction at the trailing edge, of active filament heads. Temporal analysis of time-dependent E corr distributions shows that filaments propagate at a constant speed and do not intersect.