After steel, aluminium is the most widely used metal. It is light, does not rust and is easy to cut, bend and mill. In everyday work you almost always use an alloy. This article shows the most important properties, compares the alloy groups and helps you choose.
Problem
What is aluminium?
Aluminium (chemical symbol Al) is a silvery-white light metal. It is obtained from bauxite and can be remelted again and again without loss of quality. Recycled aluminium needs only a small part of the energy required for primary production.
In air, aluminium immediately forms a thin oxide layer. It protects the metal against corrosion. Anodising deliberately strengthens this layer, which can also be coloured.
Properties of aluminium at a glance
The values apply to pure aluminium. Alloys deviate depending on their composition, above all in strength and conductivity.
| Property | Aluminium | For comparison: steel |
|---|---|---|
| Density | 2.70 g/cm³ | 7.85 g/cm³ |
| Melting point | 660 °C | ca. 1.500 °C |
| Thermal conductivity | ca. 235 W/(m·K) | ca. 50 W/(m·K) |
| Modulus of elasticity | approx. 70 GPa | approx. 210 GPa |
| Tensile strength | 60 to over 500 MPa, depending on the alloy | 360 to over 1,000 MPa |
| Magnetic | no | yes |
| Corrosion | protective oxide layer | rusts without protection |
Rounded guide values from technical literature. The material certificate states binding values.
Remember: Aluminium weighs about a third of steel. For the same stiffness, however, a component needs more cross-section, because the modulus of elasticity is three times lower.
Cause
Aluminium alloys compared
The designation to EN 573 starts with EN AW and a four-digit number. The first digit indicates the main alloying element. You will find a detailed explanation of the numbers under EN AW numbers explained.
| Group | Main element | Typical grades | Strength | Typical use |
|---|---|---|---|---|
| 1000 | Pure aluminium (≥ 99 %) | EN AW-1050A (Al 99.5) | very easy to form, best conductivity | Design sheets, hammered sheet, cladding |
| 3000 | Manganese | EN AW-3003, 3105 | easy to form, weather-resistant | Roof, facade, containers |
| 5000 | Magnesium | EN AW-5754 (AlMg3), 5083 | easy to weld, seawater-resistant | Sheets, chequer plate, vehicle and boat building |
| 6000 | Magnesium + silicon | EN AW-6060, 6063, 6082 | heat-treatable, easy to anodise, easy to machine | Extruded profiles, tubes, bars |
| 2000 | Copper | EN AW-2007 (AlCuMgPb) | excellent machinability, strong | Turned parts on automatic lathes |
| 7000 | Zinc | EN AW-7075 (AlZnMgCu1.5) | highest strength | Mould making, highly stressed parts |
Solution
Which alloy for which form?
Choose the product form first. After that, the choice narrows down almost by itself.
- Sheet for laser cutting and bending: EN AW-5754 (AlMg3). For smooth visible parts and design sheets: EN AW-1050A.
- Profile, tube and flat bar: EN AW-6060. It anodises well and has clean edges.
- Round bar for turned parts: EN AW-2007 for automatic lathes, EN AW-6082 for higher strength with good corrosion resistance.
- Highly stressed milled parts: EN AW-7075.
In practice
Which processing follows?
Bending, welding, machining and anodising each have different priorities. AlMg3 bends and welds well. 6000 series alloys are the first choice for anodising. 2007 and 7075 are less suitable for welds.
State the planned steps when you choose the material. Alloy, temper (for example H111 or T6) and dimensions belong together. For technically specified applications, the drawing or material specification takes precedence.
At a glance
- Product form defined
- Processing sequence known (bending, welding, anodising, machining)
- Alloy and temper suited to the application
- Material specification compared with the quotation
Matching products
Frequently asked questions
How heavy is aluminium?
Aluminium has a density of about 2.70 g/cm³. A sheet of 1 m² and 1 mm thickness therefore weighs about 2.7 kg. Steel of the same size weighs about 7.9 kg.
At what temperature does aluminium melt?
Pure aluminium melts at 660 °C. Depending on their composition, alloys start to melt somewhat earlier.
Is aluminium magnetic?
No. Aluminium is not magnetic. A magnet does not stick to it.
Which aluminium alloy is the most weldable?
The 5000 series, for example AlMg3 (EN AW-5754) and 5083. 6000 series alloys also weld well but lose strength in the heat-affected zone.
What is the difference between AlMg3 and AlMgSi?
AlMg3 (EN AW-5754) is a sheet alloy: easy to bend, weldable and seawater-resistant. AlMgSi (EN AW-6060, 6082) can be age-hardened and is used mainly for profiles and bars.