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Does anodize improve coating adhesion?


Does anodize improve adhesion? There seemed to be a difference in the "feel" between the standard aluminum strip and the anodized strip. I had noted more drag or friction on the anodized strip.

The goal is to improve adhesion of a varnish to the strip.

Finally, what should the anodize look like under magnification?

1100-H18, .0045-inch thick aluminum coil

MIL-A-8625 / MIL-PRF-8625 [affil link or DLA], Type II, Class 1 (thickness per Table V (.000029 to .000093)

Thanks in advance,

Larry Boever
Mechanical Products - Brookings, SD


"Adhesive Bonding of Aluminum Alloys"
by Edward Thrall
from Abe Books
or Amazon
(affil links)


"MIL-A-8625, Type II, Class 1 (thickness per Table V (.000029 to .000093)"

Hello, the above statement is a mis-quote from the spec. Actually table V states minimum thickness for type II coatings on 1100 seies aluminum as .000093".

The .000029" is for type I coatings.

Now to answer your question with a question. If adhesion is the issue, why not simply chromate?

Bill Grayson
metal finishing - San Jose, California, USA


Anodizing, preferably not sealed, will improve adhesion as compared to bare aluminum. Chromate film on aluminum is both less expensive and better for paint adhesion if the yellow color is not a problem.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina


In addition to Bill's and Jeffrey's helpful responses, please note that there is a phosphoric acid anodizing process (PAA) specifically for the purpose of adhesive bonding. One way of doing that would be under license from Boeing Commercial Products; I believe the process is called BAC5555.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

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