What is the main cause of corrosion in metals?

The primary cause of corrosion in metals is due to reactions with environmental elements. This encompasses a variety of chemical processes, most notably the electrochemical reactions that occur when metals are exposed to moisture, oxygen, salts, or other corrosive substances in the environment. For instance, when iron interacts with oxygen and water, it forms iron oxide, commonly known as rust. This process is aggravated in environments where salts or acidic conditions are present, accelerating the deterioration of metal.

While factors such as electric currents, physical impacts, and temperature fluctuations can influence the corrosion process or lead to damage, they are typically not the root cause of corrosion itself. Instead, they may act as catalysts or contribute to accelerating the rate at which corrosion occurs, rather than initiating it. For example, stray electric currents can enhance corrosion rates but are not the primary source. Similarly, physical impacts can lead to surface damage that might expose previously protected metal surfaces to corrosion but don't directly cause the corrosion process. Temperature changes can affect the rate of chemical reactions involved in corrosion, but again, they aren't the main source of corrosion. Therefore, the interaction of metals with environmental elements remains the fundamental cause.