Extensive localized corrosion of Al alloys, ranging from small pits to extensive corrosion over the entire surface, can occur in narrow crevices caused by the geometry of the structure, e.g. riveted plates, threaded joints, etc. – Contact of the metal with non-metallic solids, e.g. plastics, rubber, etc. – Deposits of sand, dirt, or permeable corrosion products on the metal surface. Differential ventilation plays an important role in the crevice corrosion mechanism, but it is not the only cause. In reality, the situation is much more complex due to acid formation within the crevice. In an aluminum crevice, corrosion shows little progress, possibly due to the precipitation of aluminum oxide, a corrosion product that restricts entry into the crevice.