6061-T6 vs 7075-T6
Should I use 6061-T6 or 7075-T6 aluminium for a machined part?
Short answer
6061-T6 is the default: 310 MPa tensile, 95 HB, machinability 9 of 10, and it welds, bends and anodises predictably. Choose 7075-T6 when the part must carry 572 MPa in the same envelope. That is 85% more strength for 4% more density, paid for in slower cutting and no weldability.
Side by side
| Property | 6061-T6 | 7075-T6 |
|---|---|---|
| Tensile strength | 310 MPa | 572 MPa |
| Yield strength (0.2%) | 276 MPa | 503 MPa |
| Elongation | 12 % | 11 % |
| Hardness | 95 HB | 150 HB |
| Density | 2.70 g/cm³ | 2.81 g/cm³ |
| Machinability (shop scale) | 9/10 | 8/10 |
| Cutting speed | 500–900 m/min (carbide) | 400–700 m/min (carbide) |
| Feed | 0.15–0.40 mm/rev turning · 0.10–0.25 mm/tooth milling | 0.10–0.30 mm/rev turning · 0.08–0.20 mm/tooth milling |
| Tooling | Uncoated or ZrN carbide, high positive rake, polished flutes | Uncoated or TiAlN carbide with a strong edge; avoid razor-sharp geometry that chips |
| Coolant | Flood for deep pockets and tapping; air blast or MQL is enough for open milling | Flood preferred - the harder alloy generates more heat at the edge |
| Surface finish | Ra 1.6 µm typical, Ra 0.4 µm best | Ra 1.6 µm typical, Ra 0.4 µm best |
| Lead time | 5–10 working days | 7–12 working days |
| Condition as supplied | T6 - solution heat treated and artificially aged at the mill | T6 - solution heat treated and artificially aged |
Machinability is our shop ranking, not a published index. Cutting data is a starting range: the holder, the depth of cut and how the part is held move it.
Choose 6061-T6 when
The part is welded or will be welded after machining
6061 is weldable to itself; 7075 is not weldable in any useful structural sense.
The part is bent, formed or straightened after machining
6061 at 12% elongation will bend. 7075 at T6 is far less forgiving of a cold bend.
The part is an enclosure, plate, bracket or housing
At 95 HB against 150 HB there is no wear problem for 7075 to solve, and 6061 machines faster.
Anodising has to build thickness inside a bore or thread
6061 anodises to a softer coating, but the build-up that has to be allowed for is the same problem on both, and 6061 is cheaper to scrap a test part in.
Choose 7075-T6 when
Strength in a fixed envelope decides the design
572 MPa against 310 MPa is the reason 7075 exists; a thinner wall in 7075 can replace a thicker wall in 6061.
The surface has to resist wear rather than corrosion
Hard anodising on 7075 gives a harder, more wear-resistant coating than the same process on 6061.
The part will not be welded and can absorb a slower cycle
Cutting speed drops from 500–900 to 400–700 m/min and the alloy is less tolerant of a rubbing tool.
The short version
If the drawing does not name a strength requirement that 6061 fails, 6061 is the cheaper, faster and more forgiving part. Specify 7075 when the load case needs it, and expect to pay for it in cycle time, tool life and the inability to weld.
What bites in 6061-T6
- ·Thin walls below 1.5 mm will bow when the part is released from the plate - specify stress-relieved T6511 stock if the pocket is deep
- ·Anodising is not a masking process: a tight bore grows, and a thread grows with it, so allowed-for threads have to be called out on the drawing
- ·Sharp internal corners in a deep pocket need the smallest cutter on the shop floor, which throttles the feed rate - a 3 mm corner radius instead of 1 mm cuts cycle time visibly
What bites in 7075-T6
- ·Not weldable - if the design needs a joint, it needs a different alloy or a mechanical joint
- ·Susceptible to stress corrosion cracking in T6; T7351 is the answer if the part sees sustained load in a wet environment
- ·Higher strength means higher cutting forces: a thin rib that a 6061 part tolerates will chatter in 7075