Summary for hexavalent chrome anodize Discussion
Hexavalent chrome in surface of chromic acid anodized parts is discussed mainly in the context of REACH/RoHS compliance and whether chromic anodize can continue after the sunset date. Julian Rees asks whether the 0.1% wt/wt threshold and the one-tonne limit mean chromic anodize is still acceptable if the chromium content in the anodic layer is low enough. In the older thread, Michael H. Williams says boric-sulfuric anodize may not match the corrosion resistance or flexibility his parts need, so any substitute would require careful testing. He says his real concern is how much hexavalent chrome remains in the surface, with health first and RoHS compliance second. The excerpt does not show a definitive numeric answer, but it makes clear that the practical issue is both regulatory interpretation and whether alternative anodizes can meet performance requirements.
Q. With the impending sunset date for the cessation of Hexavalent Chrome products, 21/09/2024 … has anyone got the figures for the amount of Hexavalent Chrome content in the anodic layer?
There’s mention in REACH of a one tonne limit related to the 0.1% wt/wt threshold?
If the amount of Cr3+ is > than 0.1% of the total weight of the part is it okay to continue with Chromic Anodise, as long as the weight is one tonne in total?
We’re changing our Automated Chromic line to Sulphuric but it’ll be interesting to know how everyone is interpreting the above?
Julian Rees
Aerospace Special Process Engineer – Truro, Cornwall UK
March 21, 2024
Multiple threads merged: please forgive chronology errors and repetition 🙂
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“The Surface Treatment & Finishing of Aluminium and Its Alloys” by Wernick, Pinner & Sheasby (1959 – 2001)
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“The Metallurgy of Anodizing Aluminum” by Jude Mary Runge (2018)
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“Surface Treatment and Finishing of Aluminum” by Robert King (1988)
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“Anodic Oxidation of Aluminum and Its Alloys” by V. F. Henley (1982)
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Q. Is there Hexavalent Chrome (Cr6+) left in the surface of anodized aluminum subject to the Chromic Acid Anodize process (Type
1)?
We have recently become concerned due to RoHS forcing us to look at alternative process’ for surface treatment of our 7075-T6 aluminum parts. Since Hexavalent Chrome (Cr6+) is a carcinogen, left over bits on or in the surface of parts we handle without protection may be a definite concern. Has anyone studied this or have a source I can reference?
I have read text exerpts that state that: “Bengough and Sutton found
0.4-0.7 chromic acid in the coatings produced by anodizing in chromic acid, while Pullen and Scott, working with coatings sealed in water, found them to consist of almost entirely anhydrous Al2O3 with less than 0.1% of chromium”. This statement obviously leaves questions as to how much, if any Cr6+ is left in the surface. The first part only says “chromic acid” while the second part says “chromium”. Any help here would be appreciated.
Michael H. Williams
Helical Products Co., Inc. – Santa Maria
2005
A. While you are investigating this, you may want to concurrently investigate Boeing’s “boric-sulfuric” replacement technology.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
2005
Q. The Boric-Sulfuric anodize is not known to be as good or better at corrosion prevention so probably won’t work for us. We also require a flexible surface that will not crack so any new process would have to be investigated and tested thoroughly. Our parts flex too much to leave it to chance. I appreciate the help but what I really want to know is how much hexavalent chrome is left in the surface. Health is my first concern, then comes complying with RoHS.
Michael H. Williams
– Santa Maria, California, USA
2005