I want to remove melted aluminium piston material from an engine cylinder with burning a hole in the cylinder!
Aluminum reacts with sodium hydroxide, and will dissolve in a basic solution, while the steel cylinder liner will be unaffected...in theory. This is totally impractical though. You need to machine out the damaged piston, either by boring or grinding the material away.
I am quite sure any acid strong enough to dissolve aluminium would be able to dissolve iron and steel, as acid + metal equations can be substituted with any metal and any acid.
