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I think folks are getting hung up on "non-cuttable". That just means you can't remove material in a typical way with a cutting tool that shears off chips of material (a saw, grinder, drill bit, etc). They're not claiming it's indestructible-- just useful for certain scenarios.

Gallium comes to mind

Of course gallium is very expensive (a few thousand $ per kilogram).

Aluminum is much less susceptible to most acids than steel. Usually it calls for hydrofluoric acid, which is very nasty stuff.