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Aluminium is known for its numerous benefits Including it's lightweight yet strong and easy to machine. But, even with these benefits, users who are considering using aluminium metal for various applications have to wonder if it's prone to rusting like some of the other equally popular metals like steel and iron.
The concern is valid, considering that rust can destroy the finish and over time weaken the structure of the metal.
Aluminium doesn't rust. But, it's essential also to note that aluminium in its pure form, is a highly reactive metal. Technically, pure aluminium dissolves when exposed to water but, it's reactive nature could also be its greatest asset.
When exposed to air, water or soil, aluminium reacts with oxygen to form a thin coat of aluminium oxide that chemically bonds to the surface of the metal. The coat is characterised by a powdery white or dull grey finish.
The coat of aluminium oxide formed hardens on to the surface and unlike rust, it doesn't flake. It keeps the metal free from corrosion unless the layer of aluminium oxide is removed.
While aluminium doesn’t rust, it does corrode. The aluminium oxide coating is highly resistant and renews itself if damaged keeping the metal relatively safe from corrosion. But some factors can cause the coat to become unstable, thus exposing the metal. The most common type of corrosion in aluminum is galvanic corrosion. It happens when aluminium comes in contact with other metals.
Galvanisation happens when different types of metal are positioned in a way that forms an electrical circuit. In this arrangement, one metal becomes stronger while the other becomes weaker. Because of its highly reactive nature, aluminium always ends up becoming the weaker metal, hence the corrosion.
Aluminium corrosion can also occur because of extreme pH levels. High levels of pH can break down the aluminium oxide coating. In this case, the coat is broken down faster than it can repair itself. To avoid corrosion, untreated aluminium should be used in areas with a pH of between 4.5 and 8.5.
Even though aluminium has an impressive set of features, like every other metal it works best in a carefully selected environment that helps it function at its best. It does not rust but, corrosion is imminent if the metal is not used in the right context.
Typically, you should not use aluminium in areas with low or very high pH. This gives the oxide coat enough time to regenerate in case of abrasion or any other mechanical damage.