Corrosion is a direct decomposition of the aluminium surface called pitting. The cause of corrosion is rooted in the insufficient natural corrosion resistance of aluminium. On this page you will find information about the most common types of corrosion, about the corrosion resistance of aluminium as well as examples of factors which can cause corrosion of aluminium.
Types of corrosion
The most frequently occurring types of corrosion are:
Galvanic corrosion: Occurs when the aluminium comes into contact with more noble metals, such as iron.
Pitting corrosion: Occurs if aluminium is in very humid environments, often with salts present (normally in dirt and filth) as well as in environments where water cannot come off the metal. Pitting corrosion is the most common form of corrosion on aluminium.
Corrosion resistance of aluminium
Corrosion resistance is an indication of how high the resistance of aluminium to corrosion is. Compared to a number of other metals, aluminium has good corrosion resistance.
For further information, the corrosion of aluminium is specified in detail in ISO standard 9023.
Oxide layer - naturally occurring corrosion protection
The oxide layer can be regarded as a protective film that forms on aluminium when aluminium comes into contact with oxygen. This layer protects the aluminium surface against corrosion in the short run. In case of mechanical damage to the oxide layer, it will repair immediately in the presence of oxygen.
If aluminium is stored in environments without major temperature fluctuations and is transported in a dry environment, where the metal is well-packaged, so that it is not possible for moisture to penetrate to the metal surface, the oxide layer provides protection against corrosion. The oxide layer is stable in the pH range 4-9. If aluminium is exposed to very acidic or very alkaline environments outside the pH range of 4-9, violent metal corrosion will occur. For example, alcohols corrode aluminium only to a very small extent, if they are free from organic acids, whereas very severe corrosion can occur if formic acid is simultaneously present. We have compiled a list of the effect different chemicals have on aluminium.
In itself, the process that takes place during the formation of the oxide layer can be regarded as corrosion of the aluminium surface. Likewise, anodisation, whose purpose is to increase the corrosion resistance of aluminium, is also a corrosion process, which, however, occurs under controlled conditions.
Aluminium in the maritime environment
If aluminium to be used in maritime environments, and thus must be sea water-resistant in order to avoid corrosion, we recommend in relation to standard EN13195:2009 the use of a large number of the alloys in the 5000 and 6000 series for maritime projects. Amongst other things, alloys 5083, 5754, 6060 and 6082 can be used.
Video showing how an aluminium item can be damaged due to water: