Aluminum oxidation and bonding

We are making a custom heatsink. Here a thin sheetmetal fin (1100 alloy) will be bonded into a slot in 6061 AL using a special epoxy.
One question that has come up is that, apparently, bonding to either oxidized or anodized aluminum is a bad idea. We've been told, by the epoxy vendor, that the epoxy will bond very nicely to the oxide layer and, eventually, separate that layer away from the aluminum fin core, thereby causing a huge reduction in thermal conductivity. A similar situation is said to exist with anodizing.
I wonder if anyone can help me understand how to go about making these things. The key data point in my mind is to know how quickly the various aluminum alloys anodize. We can certainly send them out for chemical cleaning and even sand the edge to be bonded...but how much time do you get before the oxide layer builds up to the point where you are back to square one? Is this time variable depending on the alloy being used?
Any ideas?
Thanks,
-Martin
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