A report of a new study on the use of an AC-DC-AC method for the faster evaluation of the anticorrosion performance provided by anodic films grown on an aerospace aluminium alloy, has been published recently.
The test is based on the cyclic application of a cathodic potential step, followed by a step of free corrosion, and finally the measurement of the electrochemical impedance response of the treated surface.
During the cathodic polarisation step in each cycle, alkalinisation is induced on the specimen surface, which results in attack of the porous anodic oxide. The effects of the magnitude and the duration of the cathodic polarisation step were considered, and the impedance responses measured during the various cycles were compared to the responses measured during natural immersion for longer times.
This methodology was applied for two types of anodic oxides, which are similar in thicknesses but differ in pore morphology and corrosion behaviour. Qualitative correlation was found between the electrochemical testing method and longer term immersion tests at the free corrosion potential, suggesting that the methodology can provide a faster estimation of anticorrosion performance compared to immersion test.
The study was published in Progress in Organic Coatings, Volume 144, July 2020.