Galvanizing refers to the surface treatment technology of plating a layer of zinc on the surface of metal, alloy or other materials to play a role in aesthetics and rust prevention. 

Zinc is a very active metal, which is extremely easy to oxidize, but zinc oxide is not a loose powder like iron oxide, but a dense surface layer, which prevents the zinc inside from further oxidation. 

When the surface of galvanized steel plate is damaged and the iron surface inside is exposed, zinc is more active than iron, so according to the chemical battery principle, zinc will be oxidized before iron, thus protecting the iron layer from damage.  The combination of the two is the reason for the protection of galvanized steel plates.