Aluminum and its alloys are divided into two broad classes, castings and wrought or mechanically worked products. The latter is subdivided into heat-treatable and non-heat-treatable alloys, and into various forms produced by mechanical working. The corrosion resistance of aluminum is dependent upon a protective oxide film. This film is stable in aqueous media when the pH is between about 4.0 and 8.5. The oxide film is naturally self-renewing and accidental abrasion or other mechanical damage of the surface film is rapidly repaired.