Corrosion Resistance in Various Environments

Periodic cleansing (e.g. rain) of aluminum and aluminum alloys can extend their life significantly in terms of corrosion resistance. This is especially true if the metals are exposed to environments with high salt content or other air contaminants, such as in marine and industrial locations, respectively. Furthermore, aluminum should not be stored in humid environments unless coated with a corrosion inhibitor.

Water

Aluminum is strongly resistant to corrosion in normal atmospheric environments, fresh water environments, distilled water environments and other aqueous environments. Both water containing a significant amount of carbon dioxide and polluted water, however, can be more corrosive to aluminum.

Acid and Alkaline environments

Aluminum is resistant to neutral and acidic environments, in general, because of its ability to form an oxide film. However, aluminum is more prone to corrosion in alkaline environments. More specifically, aluminum has a general resistance to corrosion in environments with a pH in the range of 3 to 8.5. Under basic (alkaline) conditions the metal is attacked much more readily than the film. Thus, if the basic medium finds a hole in the oxide film, corrosion will occur usually in the form of pitting. Conversely, under acidic conditions the oxide film is attacked more readily than aluminum, thus, if corrosion occurs it will most likely be in the form of uniform corrosion. Corrosion inhibitors can expand the pH operating range of aluminum metals and alloys in alkaline environments up to approximately 11.5.

Soil

The corrosion resistance of aluminum and aluminum alloys in soil is dependent on the nature and conditions of the underground environment. In dry, sandy soil, aluminum and its alloys are sufficiently resistant to corrosion, but in wet, acidic or alkaline soils the metals are more susceptible to corrosion.