Choosing between aluminium and steel is one of the most common decisions in designing parts and structures. Neither is better everywhere; the right answer depends on the weight, the load, the working environment and the project budget.
At a glance
| Property | Aluminium | Steel |
|---|---|---|
| Density | About 2.7 (a third of steel) | About 7.85 |
| Absolute strength | Lower (except for special alloys) | Higher |
| Strength-to-weight ratio | Very good | Good |
| Corrosion resistance | Excellent (natural oxide layer) | Needs a coating or a stainless alloy |
| Electrical and thermal conductivity | Very high | Lower |
| Melting point | About 660 °C | About 1,400–1,500 °C |
| Recycling | Very economical (about 5% of primary energy) | Recyclable |
When is aluminium the better choice?
When weight saving matters (cars, aerospace, transport), in corrosive environments, for complex cast parts made by die casting, and in heat-transfer and electrical applications.
When is steel better?
When very high strength and stiffness are needed in a small volume, when working temperatures are high, or when raw material cost is the deciding factor.
To choose the right aluminium alloy, see the alloy series and the casting grade composition table.