Pure aluminium is a light, soft metal with a density of about a third of that of steel. Pure aluminium has a high electrical and thermal conductivity.

The most common alloying elements are silicon (silumin), magnesium, iron and copper. Silicon increases the material’s castability, copper increases its machinability and magnesium increases its corrosion resistance and strength.

An obvious advantage of aluminium is that the material naturally generates a protective oxide film. This makes aluminium highly corrosion-resistant when exposed to the atmosphere.

Treatment, such as anodising, can further improve this property.
Aluminium alloys are widely used in structures where a high strength-to-weight ratio is important, such as in the transport industry. For example, the use of aluminium in vehicles and aircraft reduces weight and energy consumption.

On the other hand, the disadvantage of aluminium is that it is not stable at low or high pH, nor in chloride-containing environments. This property makes aluminium unsuitable for exposure to aqueous solutions especially under conditions with high flow. This is further emphasised by the fact that aluminium is a reactive metal; it has a low position in the galvanic series and may easily suffer from galvanic corrosion if coupled to nobler metals and alloys.

Unalloyed (pure) >99% Al
Copper is the principal alloying element, though other elements (magnesium) may be specified
Manganese is the principal alloying element
Silicon is the principal alloying element
Magnesium is the principal alloying element
Magnesium and silicon are principal alloying elements
Zinc is the principal alloying element, but other elements, such as copper, magnesium, chromium, and zirconium may be specified
Other elements. (including tin and some lithium compositions)

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