Is corrosion a physical change?
Corrosion is undoubtedly an example of
See this older answer regarding the importance of rust in the building of monumental structures.
Corrosion is a chemical change.
The most sure way to determine whether a physical or chemical change has occurred is to take a before/after "snapshot" around the change.
If the chemical composition of a material changes, then a chemical change has occurred.
Corrosion could be defined as, "... damage or destruction of living tissue or material due to a chemical or electrochemical reaction" (Chemistry.about.com).
When we boil water, the snapshot would reveal that the structure has not changed, just the distance between the atoms. Therefore, only a physical change has occurred.
When we look at an iron plate left outside, we can tell by the snapshot that oxygen has somehow worked itself into bonds with the iron. The oxygen wasn't there before! Hello rust! iron bonding with oxygen is different from iron bonding with iron, so a chemical change has occurred.