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"RoHS compliant replacement for Iridite or Alodine"
I am looking to remove all the hexavalent chromium from our telecom system in response to the new RoHS directive which becomes active in Europe next year. I am an electrical engineer, not a materials or mechanical engineer so this is all pretty new to me. Basically we have a few components of our system which are finished with a clear Iridite or are blatently chromed and I'm looking for a good substitute finish which will have the same or similar corrosion resistance and more importantly the same conductivity for EMI Shielding.
From what I've been reading a clear zinc seems to be a good choice. But I have seen some sources say that zinc uses chromium to increase the resistance to corrosion. Any help of advice would be greatly appreciated.
Engineer - USA
To my knowledge there are no standards limiting metallic chromium, either as an alloying material in stainless steel nor as chrome plating ("...blatently chromed...").
The restriction is against hexavalent chromium (chromic acid, sodium dichromate). Alodine and Iridite are trade names of chromate conversion coatings, most of which have traditionally been hexavalent chromium, but some non hexavalent conversion coatings go by those trade names too. I believe that what you are looking for is "hex-chrome-free" conversion coatings.
Zinc plated parts are very prone to 'white rust', so conversion coatings are almost always applied to zinc plated parts. Traditionally almost all of these were based on hexavalent chromium. Nowadays many are based on trivalent chromium or are chrome free. One of those is what you need.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
February 19, 2008
If you are looking for chrome free chemical conversion coatings for aluminum surfaces you might want to try either Alodine 5200 or Alodine 5700.
If you want to use material without chrome 6, you can also try Alodine T 5900 which is based on trivalent chrome.
Remark; most of these materials will not pass the one week salt spray requirement per Mil-C-5541 [link is to free spec at Defense Logistics Agency, dla.mil] which is the standard in the aerospace industry. But it might work for your application.
Aircraft part manufacturer - Papendrecht, Zuid-Holland, The Netherlands