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Conversion coating for aviation pulled rivets

Q. I'm researching methods for improving longevity of an amateur-built aircraft. Like several other posters in the archives here, I'm planning to use (as specified by the designer, and as supplied in their kit) Avex aluminum pulled rivets. The structure is all 6061. These rivets have a zinc plated steel stem, similar to the plain steel stem in common pop rivets. When the stem breaks off during installation, there's a small area of unplated steel left, and after 10 years or so this kind of rivet shows some rust, sometimes appearing in the hole left by the stem.

The stem is not needed structurally -- the design has been validated at the shear strength with the stem removed. But I am concerned about the effect on the aluminum of the rusting of the steel stem. I'd like to be able to inject something into the open end of the rivet that would provide additional protection for the broken-off end of the stem that's retained inside. Of course I don't want to attack the aluminum and rinsing inside the hole would be difficult to verify.

One idea is to fill up the hole with epoxy. Maybe epoxy with zinc chromate in it? Any other ideas for slowing down the rusting of the end of the stem?

Fred Lane
- Monterey, California
August 2, 2012