Letter 17091

Yellow chromating of GS-anodized aluminium 

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Hi,

I have an anodized ( Mil-A-8625 [link is to info about spec at TechStreet], TYPE II, CLASS 2) and black coloured product which is machine worked (afterwards) in some areas. After this operation the bare aluminium part of the product should be yellow chromated according to MIL-C-5541 CLASS 1A for maximal corrosion protection.

How to make this? Is there a perfect way to seal the anodized aluminium in a way that it will protect the anodized and black coloured areas from the attaccing Iridite 14-2 yellow chromate solution? ... or do I need to use some other protective films on the anodized areas during the chromating process? I must say that this product is pretty difficult. There is no chance to use any adhesive tapes or similar.

Best regards, Hannu Pyöriä

Hannu Pyöriä
- Helsinki, Finland

Hot nickel acetate seal should stop the chromate from absorbing into the anodic pores.

If not try: Apply the chromate with a Q-tip or cloth rag. First wipe the bare area with deoxidizing solution then rinse then wipe with the chromate until the yellow does not wipe off, then rinse again. 0.1 oz/gal Ammonium Fluoride mixed into the chromate will help. The chromate of the product you mentioned can be used at up to 4 oz/gal for wipe on application.

Robert H Probert Robert H Probert Technical Services Garner, NC, USA Editor's note:        Mr. Probert is the    author of Aluminum How-To

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