Sodium Hydroxide to be specific but unless there is just a thin film of
Aluminum, nothing is going to etch Al at any rate that is useful (at room
temp). If there are large chunks, it should not have alloyed with the steel

Are you sure of that? I have a vague memory of watching HCl go
through aluminium foil like a sneeze through toilet paper.
OP should be warned though, that ferrous metals that have been exposed
to HCL, even the fumes, REALLY want to rust.


and should just chip right off. Smaller spatters might be removed with a
scotch brite cleaning pad.