Exploring the Use of an AC-DC-AC Technique for the Evaluation of Anticorrosion Performance of Anodic Films on Aluminium Alloys

This work explores the use of an AC-DC-AC method for the evaluation of the anticorrosion performance provided by anodic films grown on an aerospace aluminium alloy. 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 polarization 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 polarization step are considered, and the impedance responses measured during the various cycles are compared to the responses measured during natural immersion for longer times. The methodology is applied for two types of anodic oxides, which are similar for thicknesses but differ for pore morphology and corrosion behaviour. Qualitative correlation is 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.