Aluminum alloys corrosion specialized coatings

In special cases where the surface hardness must be increased or chemical corrosion resistance is necessary (e.g. plasma etching with chlorine), anodized aluminum surfaces can be useful. Alloying elements, impurities, and heat treatment can influence the nature and quality of the anodized coating - typically, the more pure the aluminum alloy, the better the anodized layer. To build up a thick anodized layer on aluminum, it is necessary for the electrolyte to continuously corrode the oxide, producing a porous oxide layer. ASTM Specification B-580-73 designates seven thicknesses (up to 50 microns) for anodization. 

Zinc coating alloys with improved corrosion resistance have developed rapidly, particularly those with S or 55% aluminum additions and applied by hot dipping, those with 15% aluminum for thermal spraying, and those with nickel or small amounts of a wide range of other elements applied by plating. The special properties of each group, including improved corrosion resistance, are identified. 

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