Aluminium Alloys: Selection and Properties

Order parts made from aluminium, and you'll quickly run into a confusing range of designations. EN AW-6060, T6, AlMgSi: without a basic grasp of the system, it's hard to judge whether a given alloy actually fits the application. The wrong choice costs weight, strength, or simply money.

In brief: Aluminium alloys consist of pure aluminium with deliberately added elements such as copper, magnesium, silicon, or zinc. They're grouped into eight series (1xxx to 8xxx) and designated under the European EN AW system with a four-digit number plus a temper condition such as T6. Density and elastic modulus sit at roughly a third of steel's values, while strength varies enormously by alloy and temper.

What are aluminium alloys made of?

Pure aluminium is soft and doesn't carry much load. In the annealed state, it reaches only 70 to 95 N/mm² tensile strength, rarely enough for load-bearing parts.

That's why alloying elements are added deliberately. Copper raises strength considerably but lowers corrosion resistance. Magnesium improves corrosion resistance, especially in marine use. Silicon lowers the melting point and improves castability. Zinc delivers the highest strength values of all aluminium alloys, though at the cost of corrosion resistance.

In our sourcing projects, we regularly see customers simply order "aluminium" without specifying series or temper. The supplier then delivers a technically valid but unsuitable alloy for the application, for instance a soft 1xxx grade instead of a load-bearing 6xxx alloy.

What alloy series are there?

Aluminium alloys are grouped into eight series by their main alloying element, from 1xxx to 8xxx. The first digit of the EN AW number tells you directly which series you're looking at.

According to Material-Archiv, the 6xxx series is among the most versatile wrought alloys: readily weldable, machinable, and therefore widely used in mechanical engineering. The 5xxx series, per Material-Archiv, reaches its strength purely through cold work-hardening, since it isn't heat-treatable.

How are aluminium alloys designated?

For sourcing, the exact designation matters most, since it's the only thing that fixes composition and condition unambiguously. Under the European system EN 573, every wrought alloy gets a four-digit number prefixed with "EN AW", for instance EN AW-6060. A parallel chemical shorthand such as AlMgSi names the main alloying elements directly.

The number alone, however, says nothing about mechanical properties. That requires the temper designation under EN 515. Three letters cover most cases: O for annealed, H for strain-hardened, and T for heat-treated. H tempers apply to non-heat-treatable alloys; T tempers apply to heat-treatable series such as 2xxx, 6xxx, and 7xxx.

The T6 condition, frequently mentioned in inquiries, stands for solution heat-treated and artificially aged. In practice, it's the most commonly specified condition for load-bearing parts, because it delivers the highest achievable strength for a given alloy. Without this detail, it stays unclear whether a part ships in its soft or its strength-optimised condition. That difference can exceed 100 N/mm² in tensile strength.

What properties do aluminium alloys have?

Aluminium weighs considerably less than steel. Most alloys have a density between 2.6 and 2.9 g/cm³, against roughly 7.85 g/cm³ for unalloyed steel. The elastic modulus, at around 70 GPa, is likewise only about a third of steel's roughly 210 GPa. Aluminium parts flex more under the same load, but weigh much less.

Pure aluminium melts at 660°C, alloyed grades somewhere between roughly 500 and 660°C depending on composition. Tensile strength varies enormously: a soft 1xxx alloy barely reaches 90 N/mm², while a hardened 7075-T6 alloy exceeds 500 N/mm².

Aluminium protects itself against corrosion through a self-forming oxide layer, particularly stable in the 5xxx and 6xxx series. The 2xxx and 7xxx series, by contrast, often need an additional coating or cladding.

Even the already corrosion-resistant 5xxx and 6xxx series are frequently anodised for visible parts, to further improve surface hardness and appearance. For parts with demanding visual requirements, it's worth checking the available anodising colours already at the design stage, since changing the surface specification later is often costly.

Where corrosion demands are high and weight matters less, it's often worth comparing against stainless steel as an alternative. This applies especially to applications with constant water or chemical exposure.

Recyclability is another advantage worth noting. According to the International Aluminium Institute, remelting aluminium scrap takes only around 5 percent of the energy needed for primary production from bauxite. For buyers with sustainability requirements on their supply chain, that's a relevant factor in material selection, especially against more energy-intensive alternatives.

What should buyers watch for when sourcing aluminium parts?

A specification that just says "aluminium" leaves the supplier too much latitude. Anyone sourcing across international procurement markets should always fix the EN AW number and the temper condition. The underlying standard matters too, for instance EN 573-3 for wrought alloys. The delivery form, whether sheet, extruded profile, or round bar, belongs in the specification too.

A material certificate provides additional assurance that the delivered batch actually matches the ordered alloy. An incoming goods inspection with material verification protects against the wrong alloy slipping unnoticed into production. For machined aluminium parts, it's also worth checking the applicable general tolerances under ISO 2768. Aluminium machines differently from steel and often permits tighter tolerances.

In our practice, we repeatedly see material certificates that confirm the right EN AW number but leave out the temper condition entirely. Without that detail, incoming inspection can't reliably confirm whether the batch actually arrived in the ordered strength.

Frequently asked questions about aluminium alloys

What does T6 mean in aluminium?

T6 refers to a temper condition under EN 515: the alloy has been solution heat-treated, quenched, and then artificially aged. For heat-treatable alloys such as 6060 or 7075, this condition delivers the highest achievable strength.

Is aluminium lighter than steel?

Yes, considerably: at a density of 2.6 to 2.9 g/cm³, aluminium weighs only about a third of steel's roughly 7.85 g/cm³. For the same part volume, aluminium saves substantial weight, at the cost of lower stiffness.

What's the difference between cast and wrought alloys?

Wrought alloys (EN AW) are shaped by rolling, extrusion, or forging and are optimised for formability. Cast alloys (EN AC) are designed for flow behaviour in the mould and typically contain higher silicon content. The specification should therefore always state clearly whether a part is a semi-finished product for further processing or a direct casting, since that determines the appropriate alloy family.

Conclusion: The right aluminium alloy protects weight, strength, and cost

Aluminium alloys differ substantially in strength, corrosion resistance, and weight, depending on series and temper condition. Anyone sourcing parts who specifies not just "aluminium" but the EN AW number, condition, and standard avoids misunderstandings with the supplier. The delivered part then actually meets the required properties.

As process specialists, we at Line Up support our clients from alloy selection through to quality assurance, matching material, condition, and inspection requirements to the specific part. 👉 Book a free consultation and we'll help you find the right aluminium alloy for your next project.

Sources:

• Material-Archiv: Aluminium

• Material-Archiv: Aluminium-MgSi wrought alloy, series 6xxx

• Material-Archiv: Aluminium-Mg wrought alloy, series 5xxx

• European Aluminium: EN 573 designation system

• International Aluminium Institute: Aluminium recycling

• Wikipedia: Aluminium alloy