What exactly do aluminum and iron form in concentrated sulfuric acid during passivation reactions? Is it aluminum oxide or aluminum sulfate? Is it iron oxide or iron sulfate? A lot of people say sulfur, right?

Concentrated sulfuric acid has strong oxidation, iron and aluminum have strong reducibility; Passivation produces aluminum oxide and iron oxide (more precisely, mainly α-Al2O3,α-Fe2O3, a variant of these oxides); The surface of iron and aluminum in concentrated sulfuric acid is quickly oxidized into a dense oxide protective film, preventing the metal from further reacting with concentrated sulfuric acid.