I am trying to glue a rubber grommet to clear anodized aluminum. I am using an industrial grade instant adhesive on 6061-T6 alloy. The grommet is acting as a mechanical pivot so there is some amount of force, but not a lot. I am having difficulty getting the adhesive to stick. Do you think it is the adhesive I am using, or does the sealing of the anodic coating reduce the adhesion? Could the anodize coating be coming off?
It's probably not the fault of the adhesive and, no, the anodizing is not coming off. You have most likely touched on the problem in your question. The answer to your problem can be applied across any number of situations involving the adhesion of bonding agents or organic coatings (paints) over anodized aluminum. Anodizing can be an excellent surface for these applications, but the anodizing must be done with this in mind. The solution to your problem involves the method of rinsing and sealing of the anodic oxide after anodizing.
It is quite common to seal anodic coatings on so-called "proprietary" solutions that contain certain wetting agents (surfactants). This is done primarily to help prevent the formation of smut on the surface of the part. Smut detracts from the appearance of the product and makes it look dirty or hazy. If it is known that the anodic coating is to be used as a base for paint, or that adhesives are going to be used (caulking around windows in an architectural application, for example), the anodized parts may be sealed in either near-boiling deionized (DI) water or a dilute solution of commercially available nickel acetate. Sealing with room temperature nickel fluoride is also acceptable in this case. All three of these methods are free of surfactants. It also helps if the parts can be thoroughly rinsed in clean DI water before and after the sealing step. This will give a clean, "non-slippery" surface (no wetting agents) to which paint and most adhesives will bond. (Anodized aluminum that is to be painted is sometimes left unsealed altogether.) It would also be advisable to prime the anodized surface prior to applying the adhesive by wiping with a highly volatile solvent such as methyl ethyl ketone (MEK) or acetone to remove all dirt, fingerprints, and other possible contaminants.
Of course, you will still have to determine, by testing, which adhesive will give the best service for your application.
