Title: Process for producing improved, protective conversion coatings on aluminum and its alloys, wherein aluminum is the principal constituent

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Abstract: This invention relates to the use of sodium nitroferricyanide as a substitute for sodium or potassium ferricyanide in nitric acid acidified, hexavalent chromium-fluoride solutions for the treatment of aluminum and its alloys (wherein aluminum is the principal constituent), providing coatings having excellent corrosion-resistance, reduced surface powdering, and improved adhesion and appearance. Small amounts of sodium vanadate may also be added to effectively modify the characteristics of the deposited coatings. Controlled build-up of the protective coatings, produced by chemical reaction between the active components of the solution and the aluminum or aluminum alloy surfaces, are readily accomplished within a temperature range of 65.degree.-85.degree. F. and an immersion time of 5-10 minutes.


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