Formation of zirconium-based conversion coatings on aluminium and Al–Cu alloys

The influence of copper addition to aluminium on the formation of a zirconium-based conversion coating is investigated using sputtering-deposited substrates. Coatings formed on aluminium are ∼1.5 times the thickness of the aluminium consumed by oxidation, with an O:Zr atomic ratio of ∼2.5. Copper additions reduce the coating growth rate, especially when added in amounts above a few at.%. In contrast, the copper has relatively little effect on the oxidation rate of the substrate. Copper also promotes the formation of a layer of corrosion product beneath the coating and appears to influence the adherence of the coating to the substrate.

► Formation of zirconium-based conversion coatings is investigated on aluminium.
► Copper alloying is shown to reduce the rate of coating growth.
► Copper is shown to promote the formation of corrosion product beneath the coating.
► Compositions of coatings are determined using ion beam analyses.
► Oxidation rates of substrates are determined using sputtering-deposited layers.