Question

why galvanized article still remains proetected even after zinc coating is broken?

Answer 1

Because zinc is an active metal and it does not allow air or moisture to come in contact with the metal.
hope it helps

Answer 2

The galvanised article is protected against rusting even if the zinc coating is broken,because the outer layer of zinc will react with $O_2$ in atmosphere and forms ZnO layer,which is stronfer than, Zn layer. so,It won't allow further corrosion to the article.

          Hope it Helps