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topic 2102

Prepping Anodized Aluminum for good adhesion


(1998)

Q. How can I specify anodized aluminum to get a surface which will provide good adhesion for organic coatings such as clear lacquers? I have had inconsistent results with several aluminum suppliers. Lacquers tend to soften or completely peel off the aluminum during water or salt fog tests? Is there a primer I can apply prior to the polymer coating?

Clyde Church
aerospace - Mason City Iowa


(1998)

A. Clyde,

Generally speaking, chromic acid anodizing provides you with the best adhesion to organic coatings; other processed includes phosphoric acid anodizing and boric-sulfuric mixed acid anodizing. However, the adhesion is not dependent only on the anodizing process but also on both pretreatment and post-treatment. Post-treatment and handling procedures after anodizing are especially important to ensure good adhesion. Oil, solid, and water contamination of the anodic coating surface will definitely cause the paint peeling-off problem. Also, painting procedure and quality need to be concerned about.

Good luck.
Ling

Ling Hao
- Grand Rapids, Michigan


(1998)

A. I agree with Ling above but you also may want to consider trying an epoxy based primer and paint rather than a lacquer over an anodized surface as anodizing has an excellent adhesion quality; but as with lacquer, surface preparation is critical to making it stick and it seems to me that you're defeating your purpose to try and put a lacquer on it.

There must be an alternative to a clear lacquer finish.

I think this should be your next course of action.

ken neuts
Quebec, Canada


(1998)

A. My experience is that the largest single thing one can do to improve organic coating adhesion on anodized aluminum details, is to not seal it. Procure it from your supplier specified as non-sealed, handle after anodizing with clean cotton gloves and package with kraft paper. After receipt of the unsealed, paper wrapped, aluminum details, again handle them with clean cotton gloves and then prep and apply your organic coatings. Excellent adhesion will be the result.

Ward Barcafer, CEF
aerospace - Wichita, Kansas


(1998)

A. We have had good experience sealing surfaces with a rapid melt & resolidification process. Sealing after anodizing may significantly reduce your susceptibility to contamination prior to organic coating. At the same time, we also remove organics and other contamination from the surface. This has led to superior adhesion for hard coatings on gears. Combination of sealing and cleaning may provide you with a robust and superior surface for subsequent coating.

Kimberly Boucher
- Albuquerque, New Mexico



March 14, 2015 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am doing anodising then hot sealing and lacquer coating thereafter. I want to know if sealing is necessary in the process or it gives adverse effect for lacquer coating.

Alok Jain
- Noida, India


March 2015

A. Hi Alok. We appended your inquiry to an existing thread which addresses the subject. Kimberly makes a good point, but I am not familiar with the rapid melt & resolidification process she describes. So, for now, I'd have to go with Ward's advice to not seal the parts.

Regards,

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



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