Answer:
when you coat a metal in another metal you are protecting the inside metal. The metal metal that is being used as a coat must be more corrosive than the 1st metal. For example iron can be coated in zinc because zinc is more corrosive than iron. This is common on a ship, the iron hull is coated with blocks of zinc which will act as a barrier and will corrode instead of the iron. The zinc blocks must be renewed after a period of time however. Other ways of stopping metals from corroding include, chromium plating, coating in paint, oil or plastic.