Metal finishing Q&As since 1989

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What about just anodising for low risk situations?

2005

My company uses a mixture of aluminium coatings, black anodised (sulfuric)for highly visible (look good) parts or where light reflectance may be an issue. We use Chromate Convert - Gold (CCG) for other aluminium parts.

We are in a panic to meet the European directives (July 1/2006 deadline) because they are one of our export markets and we still haven't sorted it out.

I am having trouble finding a substitute for an alternative to CCG (Hexavalent). The problems are:
* From a longevity point of view CCG seem to be the best and there don't seem to be substitutes as good
* There still doesn't seem to be a consensus opinion on the best substitute.
* There don't seem to be standards written for the best substitutes.

So what do I do? I think I might just as well just use clear anodising for the parts which are out of view. After all, there is little point in them having better corrosion resistance than the black anodised parts.

Comments woulnd be appreciated.

Ross Parrott
water heater protection Service - Hawthorn, South Australia

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2006

There are hex-free replacements available now that claim to have the same or even better test results than the hex-containing conversion coats. So, that is an option; just make sure you find a facility that will certify that they are using those chemicals and not old hex stuff.

The other option, like you mentioned, is anodizing - you are okay with this as long as you don't get a dichromate seal, but you typically have to ask for that special, by default you should be fine. The only drawbacks are cost (anodizing will be more expensive) and lack of conductivity. With regards to clear or dyed - the dye itself has no effect on the corrosion resistance, although some shops do anodize dyed parts (especially black) to a greater thickness to increase fade resistance.

Check out letters 37583, 35088, and 34933 for more info that might help you.

Good luck!

Jim Gorsich
Compton, California, USA

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You can use anodic oxide coating to replace Chromate Coversion Coating. However the easier way is to use tested and approved Chromate Cr(+6)Free coatings with Zr salts or coatings based on Cr(+3)by European Quality Organization for Coating Aluminium.

Regards,

Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey
2006