Disclosed is a method of producing a functionalized layer and an aluminum hydroxide layer on an aluminum substrate, the aluminum hydroxide layer located between the substrate and the functionalized layer. The method comprises the steps of subjecting an aluminum substrate to a hydrothermal treatment in an aqueous solution having a pH in the range of 2 to 14 to form a layer of aluminum hydroxide on said substrate and thereafter treating said aluminum substrate with a phosphorus-containing acid selected from phosphinic and phosphonic acid to form a functionalized layer on said aluminum hydroxide layer, the functionalized layer comprised of the reaction product of said acid and the layer of aluminum hydroxide.