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Not that you asked...Thanks all for the replies. My mind can't grasp ano'd alu bonding to plywood, which is why I keep asking. Silicone I can see, but it is a flexible adhesive, which is better than nothing.
I'm wanting a secure bond because i'm using quickframe and need the plywood skin to help stiffen the span. I'm sandwiching 5/8" ply in the center of the quickframe and want to also adhere that to the QF tongue. I may silicone and screw/rivet this and stop thinking about it.
Assuming sheet material combined with the structural shape, bonding may not be as critical to the stiffening as is just the material being together in the mix. Some reasonable number of spaced pop rivets or fasteners using Nutserts will likely provide what you need. The sheet goods provide distribution of the loads. Sheet goods will not particularly add stiffness until you get to 3/4" thickness and it doesn't sound like that is your plan.
Silicone with some fasteners should be fine.