Aluminium is one of the most widely used materials for quality mechanical components in precision engineering. But how are aluminium alloys chosen?
Precision engineering selects the materials best suited to the technical drawing and end use. It would be reductive to think only of steel (carbon and special steels), because other materials perform better in certain contexts. Among the materials most used for precision parts is aluminium, or rather aluminium alloys.
Aluminium and aluminium alloys
Aluminium is a light (2.70 kg/dm³) yet strong metal whose typical colour comes from the way its surface behaves on contact with air: it oxidises and so avoids corrosion. It is particularly malleable and weldable, with high electrical and thermal conductivity.
Compared with steel, it has a lower yield strength (the point at which it deforms irreversibly) but, thanks to its lower density, it reaches high strength without adding weight. Its ability to combine with other elements allows its composition to be changed to obtain materials with different properties. This is how aluminium alloys are created.
Aluminium alloys, or light alloys, combine aluminium with another element: copper, manganese, silicon, zinc or magnesium. Whatever their specific properties, all aluminium alloys share some advantages: low density due to aluminium’s specific weight; high ductility thanks to its face-centred crystal structure; high electrical and thermal conductivity; a low melting point; and reasonable corrosion resistance that can be increased with treatments.
Which are the aluminium alloys? Properties and classification
Light alloys are divided into series according to their composition. Which are the aluminium alloys?
- 1000 series – The main component is pure aluminium (99%), offering conductivity, corrosion resistance and workability.
- 2000 series – Also known as Duralumin or Avional, it is light and hard and can be heat-treated to increase mechanical strength. How is Duralumin made? By combining aluminium and copper.
- 3000 series – Aluminium and manganese create a series with high mechanical strength but poor ductility.
- 4000 series – These alloys contain aluminium and silicon and are particularly wear-resistant.
- 5000 series – Aluminium and magnesium form the Peraluman series, characterised by ductility, weldability and resistance to melting and corrosion.
- 6000 series – Aluminium, silicon and magnesium form the Anticorodal series: machinability, weldability, mechanical strength and corrosion resistance.
- 7000 series – Sold as Ergal, it combines aluminium, zinc and magnesium and is light, machinable and resistant to load and corrosion, but has poor weldability.
How to choose an aluminium alloy
The strongest aluminium alloy is Ergal, but that does not make it the best choice for every industry. Precision engineering chooses aluminium alloys according to their mechanical properties and field of application.
For example, 99% pure aluminium alloys are chosen for heat exchangers and chemical plants. The aviation and aerospace industries rely on precision components in Avional for its strength-to-weight ratio. The food industry tends to use 3000-series alloys, while automotive and shipbuilding benefit from the Peraluman series. 6000-series alloys are used for cycling, motorcycle and rail components. The same applies to Ergal, which can also be used in aerospace and aviation.