Prepping Aluminum for good adhesion

Letter 2102

Prepping Aluminum for good adhesion

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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 peal 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 IA

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Clyde,

Generally speaking, chromic acid anodizing provides you with best adhesion to organic coatings, other process includes phosphoric acid anodizing and boric-sulfuric mixed acid anodizing. However, the adhesion is not only dependent on the anodizing process but also on both pretreatment and posttreatment. Posttreatment and handling procedure after anodizing are especially important to ensure good adhesion. Oil, solid, and water contamination on 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

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i agree with ling above but you also may want to consider trying an epoxy based primer and paint rather than a laquer over an anodized surface as anodizing has an excellent adhesion quality but as with laquer, surface preparation is critical to making it stick and it seems to me that your 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

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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 cotten 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

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We have had good experience sealing surfaces with a rapid melt & resolidification process. Sealing after anodizing may significantly reduce your susceptability to contamination prior to organic coating. At the same time, we also remove organics & 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, NM

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