Final answer:
Corrosion caused by galvanic action results from the direct contact between two different metals, leading to an electrochemical reaction where one metal corrodes and the other is protected.
Step-by-step explanation:
Corrosion caused by galvanic action is the result of direct contact between two different metals. When two distinct metals (or areas on one metal) come into contact in the presence of an electrolyte, such as salt water, a galvanic cell can be created. One metal acts as the anode and corrodes (oxidizes) at a higher rate, while the other metal acts as the cathode and is protected. This process is a type of electrochemical reaction leading to the deterioration of metals like iron rusting and the formation of a patina on copper and brass.
Methods to prevent corrosion include applying a protective coating more difficult to oxidize, or cathodic protection by using a sacrifice of a more easily oxidized metal. Galvanized steel, which is protected by a thin layer of zinc, and the use of sacrificial anodes are common methods for protecting metallic surfaces from the galvanic process of corrosion.