All dissimilar metals can produce a galvanic cell (small battery) when in close contact. Aluminum is only impervious to magnesium or Zinc coated parts. Any steel, stainless, low carbon, high carbon, what have you, is npt supposed to be in direct contact with aluminum. One of the way this is offset in aircraft maintenance and repair is with an internediate sacraficial barrier. This barrier prevents the admission of, and/or oxidation of an electrolyte for the cell. A common item used in the high heat area of an exhaust stud in milk of magnesia. The manganeze is electrolytically neutral to the aluminum, and the steel, and, once dried by heat, will keep water out of the area between them. Other common items used for this are non-chlorinated RTV, Polysulfide sealants, Zinc chromate primer, manganeze phosphate primer, and a material called Mastinox, which comes in a can with a skull and crossbones on it because it is a paste made with lead, zinc, chromium, manganese phosphate, and aluminum powder. The MSDS pretty much says don't try to have kids if you've ever been in the same room with the stuff, but it works. I've taken fasteners out of heavily exfoliated parts that were put together with the stuff 40 years ago, and the cadmium plating on the bolt looks new, the hole looks new, and the Mastinox looks new.
I'd recommend milk of magnesia for the exhaust studs. Works for me, and works on Williams-Rolls jet engines, plus any mess just washes away, and don't hurt a thing.