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topic 513

Reliable alternatives to conventional chromium conversion coatings of aluminium


(2004)

Dear Sirs,
I am looking to find some information on the possibilities of reliable alternatives to conventional chromium conversion coatings of aluminium and aluminium alloys. Due to the fact that conventional conversion coatings of aluminium involve the use of carcinogen hexavalent chromium (chromium IV) we have to find alternatives to the following surface treatment:

ALODINE 600 1000 1200
AQUABLEU 10
CHROMICOAT L25
IRIDITE

Until now we have received information only on a new CrVI free treatment developed by HENKEL showing 30-40% less corrosion resistance (measured on ASTM salt fog 5%) on unpainted parts.
If you have some information on new chromium IV free conversion coatings, please send us an E-Mail or write us at the following address. Your help will be appreciated.
Thank you very much for your cooperation.
Best Regards

Stefano Bianchini
- Florence, Italy


(2004)

30-40 percent less corrosion resistance sounds pretty good all things considered!

Chrome-free conversion coatings have been the subject of repeated articles in the trade journals for many years--and the short answer is, of course, nothing is as good as hexavalent chrome. Not as good in corrosion resistance, not as consistently reliable, not as easy to operate. But it is clearly a good idea to reduce or eliminate the use of chrome if you can.

Have you considered phosphate, with a chrome-free final rinse, as a pre-paint treatment? It may be enough.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


Dear Mr. Mooney,
Thank you very much for your answer,

I am aware that the use of a chromium VI free conversion coating of aluminium do not improve the corrosion resistance of our product and it is surely a quality downgrading. Our problem came from the new EU regulation, the TLVs limits for Chromium VI are now very low, and in the near future the use of the conventional Chromium conversion coating could be very difficult. We have carried out some test on a new processes developed by HENKEL but it show, on the best cases, 30-40% less resistance than conventional Alodine 1200. I have heard of some test carried out at U.S. Army Research Laboratories, Watertown, Massachusetts using a non-chromate conversion coating named SANCHEM. The results seem to be good but I haven't any other information on this process. Do you know something on this, if so, please could you inform me? Your help will be greatly appreciated. Thank you very much for your cooperation!

Best regards

Stefano Bianchini
- Florence, Italy


Mr. Mooney is right, there is a lot of literature out there on these alternate Cr VI free processes. SANCHEM is one company located in Chicago, IL. They appear to have done application specific testing and have several different SAFEGUARD products depending on the application. GEAE is interested in reducing Cr VI applications and plans to evaluate some of the no Cr VI offerings including SANCHEM.

Melissa Parks
aircraft engines


Sanchem, Inc. is a USA company that is, or has, commercialized a non-chromate conversion coating for aluminum. The last contact I had with them was was at a seminar where I met Dr. John Bibber, Research Director.

Gary A. Nitowski
Alcoa Center, Pennsylvania


Hi,

If you are painting after pretreatment there are various products that could be applicable depending on the performance requirements. I am going to surmise however that you will not be painting. In that case the only product that I have heard about is the Henkel product you are referring about. I would be interested in your findings.

Dan Zinman
GW International


(2004)

Have you considered anodizing the aluminum instead of chromate? There are many differences between the two conversion coatings, but we have found that in many cases when we have to eliminate chromate, anodize can be a good option.

Gordy Seppanen
materials engineer - Minneapolis, Minnesota


July 2007

Hi, readers. This thread is a bit dated. There are now some additional recognized alternatives including the TCP process.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


August 6, 2008

I did my PhD dissertation on Conversion coatings on Aluminium (UMIST, 1985) under Professor G E Thompson. I had a look at zirconium containing coating. Its corrosion resistance was poor but can be improved upon by adjusting its composition.

Makanjuola Oki
- London, UK



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