Whenever a metal corrodes in water, part of its surface loses electrons and dissolves as ions, this is an anodic reaction, while another part of the surface consumes those same electrons in a reduction reaction, the cathodic side. Both halves have to run together, connected by the metal itself carrying electrons and the water carrying ions, which is exactly the setup of an electrochemical cell. That is why wet corrosion is described as an electrochemical process rather than a purely mechanical or thermal one, and it has nothing to do with magnetism. So aqueous corrosion involves electrochemical reactions.