Question

Why does a protective layer form only on aluminium after corrosion? Why does it not happen for other metals too?

Answer 1

Dear student,
Actually copper also have a similar ability. Other metals do not have it.
Aluminum and Copper form oxide layers that adhere to the metal, and prevents the atmospheric corrosion from penetrating below the oxide layer. This protects the metal beneath the outer corroded layer. If you clean the aluminum or copper surface, the freshly cleaned surface will lose its shine and will tarnish fairly quickly, but the corrosion does not penetrate to layers below. Aluminum and copper have self-protecting corrosion mechanism, but other metals (Fe, Ni etc.) do not have this.