The kinetics and mechanism of filiform corrosion affecting organic coated Mg alloy surfaces
Christos Kousis, Patrick Keil, Neil McMurray Hamilton, G. Williams
Abstract
The filiform corrosion (FFC) of organic coated magnesium alloys is investigated using in-situ scanning Kelvin probe and time-lapse photography. FFC is initiated by injecting MgCl2, HCl and FeCl2 into a coating defect and ensuing FFC propagation rates are shown to increase as a logarithmic function of the chloride ion concentration and are strongly dependent on relative humidity. Post-corrosion surface analysis shows chloride abundance near the filament leading edge and evidence of sequestration within corroded regions behind. The FFC mechanism is consistent with chloride-induced anodic dissolution at the front coupling with water reduction on a cathodically-activated corroded surface behind.