Thanks for your question. For frequent exposure to 400°F, there are two primary options I would suggest testing. If the part is well-mated and not load bearing, a silicone transfer tape (i.e. 91022) may work well. If the part is load bearing, a structural epoxy (i.e. DP420NS) may be a better option.
With either option, surface prep is key. Rigorously degrease the aluminum with MEK or acetone, then scuff with a ScotchBrite 7447 pad, and finish with a final isopropyl alcohol (IPA) wipe.
For structural epoxy, apply adhesive for full coverage at a bondline thickness of about 0.010”; leave clamps in place during initial cure. Heat can be used to accelerate the cure.