Which type of corrosion may not be detectable by careful visual inspection of aluminum alloy parts?

Intergranular corrosion is a form of deterioration that occurs along the grain boundaries of aluminum alloys, often as a result of improper heat treatment or exposure to certain environmental conditions. This type of corrosion can be insidious because it may not be visible on the surface of the material. The damage happens within the metal structure itself, making it difficult to detect through simple visual inspection, which primarily reveals surface conditions.

Typically, pitting and uniform corrosion manifest as observable surface features. Pitting corrosion creates small pits or holes on the surface, while uniform corrosion results in an even layer of corrosion across the surface. Fretting corrosion occurs through the mechanical wear at contact points due to vibration or movement, often leaving visible signs in those areas. Intergranular corrosion, however, does not have such external signs until the integrity of the material is significantly compromised, therefore making it particularly challenging to identify without more invasive testing methods.