Comparison of the behaviours of chromate and sol–gel coatings on aluminium


Correspondence to: Y. Liu, Corrosion and Protection Centre, School of Materials, The University of Manchester, Oxford Road, Manchester M13 9PL, UK.



Differences between chromate conversion coatings and sol–gel coatings formed on aluminium and aluminium–copper alloys are highlighted with respect to the formation of cracks, the effect of the substrate composition on coating thickness and the influence of curing in air on coating re-growth. For sol–gel coatings, it is shown that (i) cracking can be eliminated by inclusion of a sufficient amount of organic moieties, (ii) the coating thickness is unaffected by copper and (iii) coating re-growth occurs readily after curing. These attributes are shown to contrast with the significantly different behaviours of chromate conversion coatings. Copyright © 2012 John Wiley & Sons, Ltd.