Pure aluminium is soft, ductile, corrosion resistant and has a high electrical conductivity, see Table 1. In consequence it is widely used for foil and conductor cables, but alloying with other elements is necessary to provide the higher strengths needed for other applications.
Table 1. Typical properties for aluminium
|
Property
|
Value
|
|
Atomic Number
|
13
|
|
Atomic Weight (g/mol)
|
26.98
|
|
Valency
|
3
|
|
Crystal Structure
|
Face centred cubic
|
|
Melting Point (°C)
|
660.2
|
|
Boiling Point (°C)
|
2480
|
|
Mean Specific Heat (0-100°C) (cal/g.°C)
|
0.219
|
|
Thermal Conductivity (0-100°C) (cal/cms. °C)
|
0.57
|
|
Co-Efficient of Linear Expansion (0-100°C) (x10-6/°C)
|
23.5
|
|
Electrical Resistivity at 20°C (µΩcm)
|
2.69
|
|
Density (g/cm3)
|
2.6898
|
|
Modulus of Elasticity (GPa)
|
68.3
|
|
Poissons Ratio
|
0.34
|
The main alloying elements are copper, zinc, magnesium, silicon, manganese and lithium (Table 2). Small additions of chromium, titanium, zirconium, lead, bismuth and nickel are also made and iron is invariably present in small quantities. There are over 300 wrought alloys with 50 in common use.
Aluminium's range of properties can be found in this impressive array of commercially available alloys. The composition and logic of those alloys are regulated by an internationally agreed classifications system or nomenclature for wrought alloys and by various domestic nomenclature schemes for the casting alloys.
The wrought scheme is as follows. Each registered alloy is described by a four digit number, with a further letter and number indicating the temper, or condition of the alloy. For example, 6082-T6 is a medium strength grade based on the aluminium-magnesium-silicon family, in the fully heat-treated condition.
Table 2. Aluminium alloys
|
Wrought alloy designation
|
Major alloy elements and typical characteristics
|
|
1xxx Series
|
Minimum 99% aluminum
High corrosion resistance. Excellent finishability. Easily joined by all methods. Low strength. Poor machinability. Excellent workability. High electrical and thermal conductivity.
|
|
2xxx Series
|
Copper
High strength. Relatively low corrosion resistance. Excellent machinability. Heat treatable.
|
|
3xxx Series
|
Manganese
Low to medium strength. Good corrosion resistance. Poor machinability. Good workability.
|
|
4xxx Series
|
Silicon
Not available as extruded products.
|
|
5xxx Series
|
Magnesium
Low to moderate strength. Excellent marine corrosion resistance. Very good weldability.
|
|
6xxx Series
|
Magnesium & Silicon
Most popular extrusion alloy class. Good extrudability. Good strength. Good corrosion resistance. Good machinability. Good weldability. Good formability. Heat treatable.
|
|
7xxx Series
|
Zinc
Very high strength. Good machinability. Heat treatable.
|
|
8xxx Series
|
Miscellaneous alloys e.g. aluminium-lithium alloys
|
Alloys fall into two main groups. The work-hardening alloys, where strength is achieved by the amount of "cold work" applied to the alloy for example, by rolling, and heat-treatable or precipitation hardening alloys, where the strength and properties are achieved by heat treatments of varying complexity.
Sources
Text: International Aluminium Institute, The Aluminium Extruders Council, AZoM
Photos: Alloy Tech