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Q. We use alodine on 5053 aluminum and use a water based coating. We want to change to powder but we are also having to meet the Rohs requirement that does not allow hexavalent chrome in the alodine. Have you found or know of an alternative to the Alodine that would give good adhesion and good Florida exposure. Thanks. J.D.


A. A brief background for readers not familiar with your problem. RoHS (Restriction of Hazardous Substances) is a European directive that minimizes or eliminates some chemicals altogether. They are lead, cadmium, hexavalent chromium and mercury along with two organics, polybrominated biphenyl (PBB) and polybrominated biphenyl ether (PBDE). It takes effect July 1, 2006 and is geared specifically towards the electronics community, although the automotive sector in Europe also has very similar restrictions under the End of Life Vehicle Directive.

Regarding your specific situation, non-chrome conversion coatings have come a very long way in the last decade and in many cases are considered to be a close match in performance to the chromate systems they are replacing. You have the additional benefit of using a paint or coating over you conversion coating, so I would anticipate the switch for you to be almost seamless. If there is an area where some of the non-chrome conversion coatings still struggle a little, it is in corrosion protection when used alone, without further coating.

In your case, the conversion coating will help in paint adhesion and provide adequate corrosion protection in cases where your paint becomes damaged. South Florida exposure should be largely the same, since that test is meant partially for corrosion, but probably more to asses the ultraviolet degradation of paints and coatings. You should probably watch your paint change more closely than the switch from the chrome to non-chrome conversion coating. Choosing the wrong resin type for your coating (such as an epoxy) will have much more effect on UV degradation and South Florida failure than the pretreatment.
I would suggest going to the Products Finishing web site (www.pfonline.com) and clicking on the Supplier tab. Then follow that by selecting the Cleaning & Pretreatment category. Then select Cleaning & Pretreatment Chemicals and finally, Chromium-Free Conversion Coatings for Aluminum. Listed there are all the suppliers that I am aware of (and a few I wasn’t) that supply non-chrome conversion coatings. You could contact any of them to initiate your project. I am sure they would like the opportunity to test coat one of your products.