"Ed Huntress" fired this volley in
:


It's a noticeable problem in aluminum diecasting, where the aluminum
impinges on the steel with some pressure and cuts right through the
oxide to the parent metal.

It's not the high-temperature "corrosivity" of aluminum that's at issue.
What happens is, iron oxide and aluminum enter into a Goldshmidt reaction
-- that is, the combination is Thermite.

This has the side effect of raising the interface temperature sharply,
further increasing the solubility of the iron in the aluminum.

Aluminum will dissolve in iron, and vice versa, even at temperatures
far below the melting point of iron. The two metals can exist in a
very wide range of solutions.

Yup. The best miniature soldering irons have tips masked with aluminum
plating to prevent any but the very tip to become tinned.

LLoyd