You mention embedding the aluminum inside carbon. Is this a layer of metal in a composite laminate? A washer or some other sort of component?
Aluminum has fairly negative electrode potential (of common metals only zinc and magnesium are worse). You need to electrically insulate the aluminum from galvanically dissimilar materials (especially carbon; only platinum and gold are more positive or noble). The aluminum must not touch the carbon and must not be joined to it by a conductor (e.g., moisture, and the moisture that infuses into a thermoset polymer matrix can be enough to give problems, especially if the resin has microcracks or crazing).
Aluminum should be being protected from the environment anyway with anodize, prime and paint, but this is not enough if carbon is about. A better material than just epoxy is needed to protect aluminum from carbon. As was noted in that thread a layer of thin glass fabric with primer on the aluminum seems usually to last ok even though the glass is fairly porous. The additional distance the glass adds may be a significant factor (if you could arrange (and guarantee) a really thick gel coat roughly twice the thickness of the glass layer it might work about as well).
Titanium and good stainless steel have better adhering oxide layers than aluminium plus their constituent elements are less negative than aluminium, and generally titanium and good stainless don't need additional protection (over and above their protective oxide) and can be used bare. Some of the martensitic and precipitation hardening stainlesses are not so good; for instance, it may be worth protecting 440A, B or C or 17-4PH, although in practice they'll usually be ok. Guaranteed good stainlesses are A-286, as used for many aerospace fasteners, and austenitic (300-series).
Copper (and brass and bronze) is not so galvanically negative as aluminium but is more so than titanium, and copper has no protective oxide layer and it should be reasonable well insulated from any carbon. A brass bush can be inserted into a hole in a thick carbon laminate with a coating of primer and a sealant.
Whoever is responsible for design rules concerning avoidance of galvanic corrosion should have set down pretty clear ones for what needs protecting from what and how, especially carbon fiber.