I'm no engineer so not that much help with material selection.

I do work with composite and do alot of polyurethane and etc silicone casting. Most cast polyurethanes will usually need either a very good mechanical key or primer/adhesive to help adhere to aluminium (due to aluminiums oxide layer on the surface).
On the other hand, moisture cure polyurethane and silicone has much better bonding characteristics, reason's unknown to me!? 2 part cast PU or silicone are available in a much wider range of shore hardness though...

Food for thought, maybe.