Question

What are advantage and disadvantage of corrosion

Answer 1

Surface corrosion forms an oxide layer. It acts as a barrier for air and moisture and thereby preventing the inner metal from corrosion.
Some metals like zinc act as sacrificial anodes to prevent corrosion to other metals.
Galvanic corrosion is the principle that is used in batteries. Here, two metals carbon and zinc are intentionally mixed together in a electrolyte solution where zinc corrodes faster in order to generate electrical charge.

Answer 2

Corrosion is an electrochemical process of refined metals coming back to a thermodynamically stable oxides form. As the ores are at a lower energy level it makes them stable. The same process occurs with aluminum or stainless steel. This inert layer of oxide is thin, tough and stable. It protects the metal from further corrosion. This phenomenon is used for a thin film formation in some metals by dipping them in acids to form such oxide layer. It is called passivation.

Edit-1:The old zinc-carbon batteries were powered due to corrosion of zinc!Image courtesy

2. Drrafting the answer in hurry, I forgot to mention I am employed by this multi-billion dollars corrosion protection industry! I'm one of the beneficiaries of it and grateful for it.

Will update further