Metal finishing Q&As since 1989

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Anodize vs. clear conversion coat

What are the material property differences when a aluminum extrusion is treated with non-chromium conversion coat vs. clear anodize. I'm using this aluminum in a heatsink application and cannot use anodize because of electrical grounding properties. Clear conversion coat provides the ground path I'm looking for, but anodize sheds heat better.

Greg Mlotkowski
- Farmington Hills, Michigan, USA
2005

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First of three simultaneous responses -- 2005

Dear Greg

Clear conversion coating is a chemical treatment where you are dipping the samples in a solution containing chrome III. This coating is only measured by weight instead of micron. The corrosion resistance is well and it is electrical conductive. The formed layer consist of a chromate/aluminium oxide film.

Clear anodizing is a coating formed by a current, so this a electrochemical treatment where you are dipping the samples in a acidic solution and then adding a electrical power. This coating is measured by micron. The formed layer consist of an non-conductive aluminium oxide film.

Please feel free to ask for a deeper explanation, if this have you interest.

Anne Deacon Juhl
- - Trustrup Denmark

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Second of three simultaneous responses -- Why not mask the threads or areas to allow grounding and then anodize?

Bill Grayson
- San Jose, California
2005

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Third of three simultaneous responses -- Everything that I have read says that the heat dissipation is going to be very similar between the two processes. You can have clear on the contact side, mask that side and anodize it. Trace leakage under the masking can not be seen and will not affect the conductivity of the rest of the part, so it does not have to be a jewelry quality mask job, so should be only slightly more expensive.

James Watts
- Navarre, Florida
2005

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Would you please let me know what the difference is between anodizing and chemical film.

Andrew Lau
- Huiyang
2005

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2005

Chem film is the same thing as chromate conversion coat, Andrew, so see the top entry on this page.

A follow-on question to some of the comments:

From descriptions of both anodizing and conversion coatings, a couple of the purposes for each of these processes is corrosion resistance and better adhesion of additional paint or powder coat. What would be the purpose of using both processes on a part? (Material is aluminum, either 5052 or 6061.)

John Pervorse
- La Jolla, California, USA

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 13, 2010