Corrosion resistance of anodic coatings studied by scanning microscopy and electrochemical methods

The paper refers to examination of corrosion resistance improvement of aluminium based material subjected to a sealing procedure. The tests were carried out for non-sealed and sealed anodic coatings using both scanning microscopy and electrochemical techniques. The correlation between electrochemical parameters (i.e. corrosion potential (Ecorr), corrosion current density (jcorr)) and contact potential difference (CPD) was examined. It was found that in the first approximation jcorr as well as Ecorr change linearly with CPDav (average CPD). It was shown also, that a decrease of jcorr and an increase of CPDav caused by anodic oxidation can be explained by an increase in oxide thickness. Further increase in CPDav observed for sealed coatings is related to a decrease of root mean square roughness and/or disappearance of surface anisotropy.