Aluminium grades are not interchangeable: 7075 is nearly twice as strong as 6061, with sharp differences in cost, machinability and finishing. Here is how to pick the right alloy for a machined part — with the numbers behind each call.
Side by side (T6 temper)
| Property | 6061-T6 | 7075-T6 |
|---|---|---|
| Tensile strength | ~310 MPa | ~572 MPa |
| Yield strength | ~276 MPa | ~503 MPa |
| Hardness | ~95 HB | ~150 HB |
| Density | 2.70 g/cm³ | 2.81 g/cm³ |
| Machinability | Excellent (the benchmark) | Very good (chips break cleanly) |
| Weldability | Good | Poor, not for arc welding |
| Corrosion, bare | Good | Lower, usually coated |
| Anodizing | Clean, even colour | OK; Type III common, colour can vary |
| Relative cost | $ | $$ (~1.5–2× in bar) |
| Typical use | Brackets, housings, frames, general | Aerospace, high-stress, moulds |
6061, the workhorse
6061 offers excellent machinability, corrosion resistance, weldability and an even anodized finish. It is strong enough for most brackets, housings and general parts, while remaining the more economical and faster choice to machine.
7075, the strong one
7075 provides nearly twice the tensile strength of 6061, making it the default for structural, load-bearing and aerospace parts. The trade-offs: it costs more, does not weld well, and corrodes more easily when left bare — so it is normally anodized (often Type III, a thick hard-anodize coating) or plated for protection.
Three quick mistakes
- Choosing 7075 when 6061 is sufficient — it raises material and machining cost while sacrificing weldability and an even anodize colour.
- Trying to weld 7075 — it is highly prone to hot cracking in arc welding, so design joints to be bolted or mechanically fastened instead.
- Leaving 7075 bare — always specify an anodized or plated finish to guard against corrosion and stress-corrosion cracking (SCC), the cracking that can occur when a stressed part sits in a corrosive environment.
Quick rule
Strength- or weight-critical? Choose 7075. Driven by cost, corrosion resistance, weldability or general use? Choose 6061. If you are unsure, send the part and we will advise during DFM (design-for-manufacturing) review.
