Question

is corrosion harmful every time

Answer 1

What are the harmful effects of corrosion? Corrosion is the destructive attack of a material by electo/chemical reaction with its environment. For most of us, corrosionis the degradation of metals that is often called rust. The corrosion resistance of anymaterial depends on the environment to which it is exposed.

Answer 2

no ..... corrosion in aluminium is beneficial as it prepares a coroded layer aluminium oxide which prevents further corrosion