Mild steel, stainless or aluminium?
Materials. Published Oct 7, 2026 by ManuFx.
Three metals cover most fabricated parts. A short guide to their strength, weight, rust resistance and cost.
TL;DR
- Mild steel: strong, easy to weld and the lowest cost, but it must be coated.
- Stainless steel: resists rust without a coating, at a higher price.
- Aluminium: about a third of the weight of steel, and it resists corrosion.
Mild steel
Low-carbon steel is strong, easy to cut, bend and weld, and costs the least of the three. It is the usual choice for frames, brackets and structures.
It rusts when left bare, so it is painted, powder coated or galvanized.
Stainless steel
Stainless steel holds at least 10.5% chromium, which forms a thin film on the surface that keeps rust out and heals when scratched.
Grade 304 suits most uses. Grade 316 adds molybdenum for salt water and chemicals. Both cost more than mild steel.
Aluminium
Aluminium weighs about a third of what steel does and resists corrosion without a coating. It carries heat and electricity well.
It is less stiff than steel, so a part may need thicker sections to carry the same load.
Choose the metal for where the part will live, not only for what it must carry.
How to choose
Start from what the part has to do.
- Load: steel, where strength and stiffness matter most.
- Weight: aluminium, where every kilogram counts.
- Surroundings: stainless or coated steel, where the part meets water or chemicals.
- Budget: mild steel with the right coating is often the lowest cost.