Galvanic Corrosion

Galvanic corrosion is an accelerated electrochemical attack happening when two different metals make electrical contact, while both are immersed in a common, conductive electrolyte (like seawater or moist soil). 

The fundamental principle relies on the Galvanic Series—a ranking of metals by their electrical potential. The metal that is more active acts as the anode and undergoes rapid oxidation (corrosion), sacrificing itself. Conversely, the more noble metal acts as the cathode and is protected. A critical factor is the area ratio: a small anode connected to a large cathode dramatically concentrates the corrosive attack on the anode.