1. Pitting corrosion
Pitting corrosion, also known as hole corrosion, is a very localized corrosion form that produces needle-like, point-like and hole-like shapes on metals. Aluminium will undergo pitting corrosion in the atmosphere, fresh water, and neutral aqueous solutions. In severe cases, it can also lead to perforation, but the corrosion holes may eventually stop developing, and the amount of corrosion remains at a limit value. Pitting corrosion is a unique form of anodic reaction and is an autocatalytic process.
2. Galvanic corrosion
Galvanic corrosion is also a characteristic corrosion form of aluminum. The natural potential of aluminum is very negative. When aluminum is in contact with other metals, aluminum is always in the anode to accelerate the corrosion. Galvanic corrosion is also known as bimetallic corrosion, and the severity of corrosion is determined by the relative position of the two metal potential series.
3. Crevice corrosion
Crevice corrosion is the acceleration of corrosion in the crevice due to the action of the differential gas-filled battery, while there is no effect outside the crevice. Crevice corrosion has little to do with alloy type, and even very corrosion-resistant alloys can develop crevice corrosion. In recent years, the mechanism of crevice corrosion has been further studied, and the acidic environment at the top of the crevice is the driving force of corrosion.
4. Intergranular corrosion
Intergranular corrosion means that pure aluminum does not proliferate intergranular corrosion. The cause of intergranular corrosion is related to improper heat treatment. Alloying elements or intermetallic compounds are precipitated along the grain boundaries. Compared with the grains, the anode constitutes a corrosion cell, causing intergranular corrosion. Corrosion accelerates.
5. Filiform corrosion
Filamentous corrosion is a kind of sub-film corrosion, which develops under the film in a worm-like manner. This film can make the paint film and other layers, and generally does not occur under the anodized film.

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