Require a Replacement to Alodine for Aluminum

Consider Tri-valent Chromium Pretreatment an alternative to hexavalent chromate treatments, a known carcinogen.

Formulated by Naval Air Warfare Center (NAVAIR), POC’s: Dr. Vinod Agarwala, C. Matzdorf

Alodine is not much of a coating, so tri-valent chromes might work, but I have heard they leave much to be desired. Do you have no option of putting electric current through the base part? Zinc brush plating seems safe and functional. A hot steam gun can also increase the native oxide on aluminum from 20 angstroms to over 100 angtroms.

Otherwise, you may simply want want a lacquer or paint coating.

A useful protective paint for aluminum is Zinga:

What are the coating performance requirements and the reason for not wanting to use Alodine: hex. chrome, color, lack of abrasion resistance…?

To cover bare areas on an anodized part, the logical solution is ‘spot’ anodizing. This can be done either by brush anodizing or conventional immersion anodizing. Helps to have an experienced anodizer, but basically, just deox. the bare area and then anodize. Do not exceed the initial voltage. This works for both conventional & hard anodize. If you are on the cautious side, you can protect the initial anodize with a peelable plastisol maskant.

Plastisols are PVC-based. You might not want to use them near aluminum.

The 'plastisols' used for masking in the metal finishing industry are quick-drying, solvent-based solutions of PVC particles, whereas 'plastisol' in the plastics industry means a vinyl resin dispersion which reacts upon heating to 300-350^oF. I would agree that the latter could harm Al. Also, pre-OSHA & -Clean Air Act, masking plastisols may used trichloroethylene as solvent, which is corrosive to Al (if not for the quick evaporation). However, for the last 30 years, there has been a trend to solvents less hazardous to human health, the environment and Al. Many peelable maskants are now water-based, but PVC types retain some popularity due to good chemical resistance and quick drying.

We have tested the Tri-valent Chromium on aluminium are a primer and a stand allone coating with very good success.

Thanks to all for sugegstions. Have found a conversion coating called safegard6100 that works.