Hi Pat,
The resin should stick to the metal provided it is clean. You will need to remove any tarnish or other residue, otherwise, the resin may not stay on the surface. Sanding or using something like a dremel tool, in order to get down to fresh metal, would be best. Otherwise, if you have an aluminum tarnish remover (do they even make such a thing?), that could be an alternative. Make sure your piece is clean and dry (wash with a good detergent) before applying the resin.
Would you mind letting us know how it goes?