The main reason for anodizing aluminum after it has been electropolished with an alkaline or fluoboric acid bath type electrolyte is that the oxide film formed on the metal surface does not offer satisfactory protection against corrosion. When aluminum is electropolished in solution containing phosphoric, sulfuric or chromic acid its surface has higher resistance to corrosion and does not necessarily require an anodizing treatment subsequently. In solutions containing phosphoric, sulfuric and chromic acids, the chromic acid concentration may vary within wider limits – 37 percent for phosphoric acid, 15 – 46 per cent for sulfuric acid and 4 – 12 per cent for chromic acid. The optimum composition of the electrolyte recommended for electro polishing of Duralumin contains 43 per cent phosphoric acid, 43 per cent sulfuric acid, 3 per cent chromic acid and balance water. In the case of pure aluminum an electrolyte which does not contain any sulfuric acid may be used but it may leave some risk of pitting.
More about anodizing process and metallic impurities type of metallic coating such as on chrome plating, bright chrome plating, dull black chrome plating, white chrome plating, gold color chrome plating, silver plating, gold plating, copper plating, anodizing, aluminum anodizing, black anodized, red anodized, yellow anodized, bronze color anodized, silver anodized, gold anodized, zinc coating, galvanizing.
More about anodizing process and metallic impurities type of metallic coating such as on chrome plating, bright chrome plating, dull black chrome plating, white chrome plating, gold color chrome plating, silver plating, gold plating, copper plating, anodizing, aluminum anodizing, black anodized, red anodized, yellow anodized, bronze color anodized, silver anodized, gold anodized, zinc coating, galvanizing.