Abstract
Light metals such as Mg and Al are of high interest for lightweight engineering
applications in various industries. However, their susceptibility to corrosion, poor
tribological properties, and moisture sensitivity limit their direct use. Plasma electrolytic
oxidation (PEO) is a commonly used process to overcome these challenges by
generating ceramic-like oxide layers that significantly enhance surface protection.
High-resolution in-situ atmospheric corrosion studies using a scanning Kelvin probe
(SKP) were performed to evaluate the electrochemical behaviour and corrosion
protection ability of PEO coatings in different humid atmospheres on AlSi7, AlMg3, and
AZ801. Measurements were conducted in both nitrogen and synthetic air environment
at 95% relative humidity (RH) with and without 3 wt. % NaCl electrolyte. Results
showed that, for PEO-coated AlSi7 and AlMg3, scratch regions exhibited gradual
stabilization or partial passivation over time, despite initial drops in Volta potential upon
exposure to electrolyte or oxygen. Moreover, PEO-coated AZ80 maintained or
increased its potential even when scratched down to the base metal in a chloride-rich
environment indicating that the PEO layer substantially hindered cathodic reactions by
limiting oxygen reduction at the defect site. Overall, these results demonstrate that
PEO coatings significantly enhance corrosion protection on AlSi7, AlMg3, and AZ80
by limiting cathodic reactions. The findings highlight PEO’s potential to extend service
life and reliability in demanding applications where lightweight alloys are subject to
aggressive environmental conditions.