What are five common forms of corrosion?

The identification of five common forms of corrosion is fundamental for understanding how materials degrade over time in aviation environments. The correct choice lists intergranular, stress, fretting, and dissimilar metal corrosion, each of which has distinctive characteristics and mechanisms.

Intergranular corrosion occurs along the grain boundaries of metals, which can weaken the material by promoting localized attack when conditions such as temperature and composition cause the boundaries to become susceptible to corrosion. This form is especially problematic in heat-treated alloys.

Stress corrosion cracking involves the combined influence of tensile stress and a corrosive environment, leading to unexpected failures at stresses lower than the material's yield strength. It is critical for A&P mechanics to recognize this type of corrosion, as it can lead to catastrophic failures in critical components.

Fretting corrosion is a result of small, relative movements between contacting surfaces under load. This movement can disturb protective oxide layers, allowing corrosion to initiate and propagate despite the absence of significant movement or a corrosive fluid.

Dissimilar metal corrosion occurs when two different metals are in electrical contact in the presence of an electrolyte, resulting in galvanic corrosion where one metal becomes anodic and deteriorates faster than the cathodic metal. This is particularly important in aircraft maintenance as many components are