How is aluminium made?
Aluminium has unique characteristics. For instance, it is light, corrosion-resistant and non-magnetic. That is why this material is used in many different sectors, like automotive, packaging and… windows and doors. To produce aluminium, the element aluminium oxide is of course key, but its characteristics can be further improved by adding small amounts of other elements. Let’s delve a little deeper into the production process of aluminium.
As mentioned above, aluminium is produced from aluminium oxide. Aluminium oxide is the most abundant metallic element in the earth's crust, making up 8% of our planet’s soil and rocks. The ore with the highest concentration of aluminium oxide is bauxite. It is found in various tropical and subtropical regions all over the world. How is bauxite extracted? It is done by surface mining, whereby it is removed directly from the surface without digging down.
Two-stage production of aluminium
The production of aluminium is carried out in two phases:
- Chemical (Bayer) process: the bauxite ore is ground down and refined to obtain aluminium oxide.
- Electrolytic (Hall-Heroult) process: the aluminium oxide is smelted to release pure aluminium. This liquid aluminium is cast into ingots.
The result is what we call ‘primary aluminium’.
Finetuning the characteristics of aluminium
The aluminium material has unique characteristics such as:
- High strength-to-weight ratio
- Corrosion resistance
- Heat conducting
These characteristics can be further improved to better suit the needs of the application. How? By adding small amounts of other elements. The results are different types of aluminium, categorized by alloy types. For extrusion applications for windows and doors (outlined below), the aluminium alloy 6060 is mostly specified, which mainly includes the additional elements Mg (magnesium) and Si (silicon). These elements improve the strength and corrosion resistance of the aluminium.
Extruded aluminium profiles
Systems for aluminium windows and doors are made using extruded profiles, or tubes. To create these extruded profiles, the (pre-heated*) aluminium is pushed through a die. This die gives the shape to the profile. It is a continuous process, creating very long lengths of profiles. These profiles are cut to the desired length, stretched to strengthen the profile and thermally treated to ensure that the elements in the alloy are well distributed throughout the profile.
The aluminium alloy is very important to guarantee both its aesthetic and technical characteristics. Aesthetically, the surface of the aluminium should not show pollution and should have an even colour. Technically, the aluminium alloy should flow well through the die to create the tubular profiles, conferring high corrosion resistance and strength.
* The aluminium used for extrusion is cast in billets. These billets are preheated to +/- 450°C before extrusion. This is the plastic phase of aluminium (melting temperature is 660°C).
About the corrosion resistance of aluminium
When aluminium is exposed to air, it almost instantaneously creates a protective oxide layer in a naturally-occurring reaction. This corrosion- resistant layer can be further enhanced with surface treatments such as anodisation where an electrochemical aluminium oxide layer is formed on the material, even further improving its resistance to corrosion.
Aluminium is infinitely recyclable
Like other metals, aluminium is 100% recyclable. By being mindful of the various types of alloys during the recycling process, aluminium does not lose its unique characteristics. This means you can recycle it endlessly without any loss in quality. That is why we developed a clear focus on the quality of aluminium recycling. This allows us to close the aluminium loop by recycling old window profiles and creating new profiles infinitely.