Corrosion resistant trivalent chromium phosphated chemical conversion coatings
AssigneeUnited Technologies Corporation
InventorPromila Bhatia
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Abstract
An acidic aqueous solution containing a water soluble trivalent chromium compound is provided with a additive for improving corrosion resistance and reducing precipitation of trivalent chromium over time. A suitable additive is nitrilotris (methylene) triphosphonic acid (NTMP).
Claims21
An acidic aqueous solution which is free of hexavalent chromium comprises a water soluble trivalent chromium compound, a water soluble fluoride compound, and an additive for improved corrosion resistance properties.
A process for preparing a corrosion-resistant-trivalent chromium coating on aluminum and aluminum alloy substrates comprises treating the substrates with an acidic aqueous solution, which is free of hexavalent chromium, comprising a water soluble trivalent chromium compound, a water soluble fluoride compound, and an additive for improved corrosion resistance properties.
Dependencies are inferred from the claim text.