The paper describes research into a DERA patented Double-Immersion Process (DIP) technique, which has been developed to improve the corrosion resistance of unsealed anodic films on aerospace aluminium alloys. The aim is to develop a chromate-free treatment for aluminium alloys as a potential substitute for chromic acid anodising. The research methodology is based on the incorporation of environmentally acceptable corrosion inhibiting pigments within an anodic film itself produced by a non-chromate anodising process. The resulting anodic films possess high corrosion resistance and have the added advantage of potentially reducing reliance on the use of paint schemes containing chromate pigments and promoting the use of chromate-free primers. The Double-Immersion Process involves two consecutive steps, firstly, immersion in a solution of metallic cations such as nickel, zinc or cerium, and, secondly, immersion in a solution of metallic anions such as molybdate, tungstate or metavanadate. Neutral salt fog corrosion tests conducted on anodised alloys that have been treated using this two-stage post anodising process indicates that the highest levels of corrosion resistance are obtained for zinc-vanadate and nickel-vanadate combinations, which were at least as protective as a conventional hot dichromate seal.
A chromate-free post-anodising treatment for aluminium alloys using a double-immersion process
2000
13 Seiten, 1 Bild, 7 Tabellen, 13 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
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