Key takeaways
- The temper follows the alloy: 6063-T5 means alloy 6063 in temper T5.
- T5 = press quenched + artificially aged. T6 = solution heat treated + artificially aged.
- T4 is softer and formable — bend first, then age to T6.
- T66 (EN) is a 6060/6063 temper with higher properties through process control.
- Suffixes 510/511 mean stress-relieved by stretching (e.g. 6061-T6511).
The letters and numbers after an alloy — the temper designation — tell you how the metal was processed and therefore what properties to expect. The system is defined in ANSI H35.1 and EN 515, and it matters as much as the alloy itself.
Basic tempers
| Code | Meaning |
|---|---|
| F | As fabricated — no property control |
| O | Annealed — softest condition |
| W | Solution heat treated, unstable (ages at room temperature) |
| T | Thermally treated to a stable temper (T1–T10) |
| H | Strain hardened — used for non-heat-treatable alloys, not 6xxx extrusions |
T tempers
| Temper | Process |
|---|---|
| T1 | Cooled from shaping and naturally aged |
| T2 | Cooled from shaping, cold worked, naturally aged |
| T3 | Solution heat treated, cold worked, naturally aged |
| T4 | Solution heat treated, naturally aged |
| T5 | Cooled from shaping, artificially aged |
| T6 | Solution heat treated, artificially aged |
| T7 | Solution heat treated, overaged or stabilised |
| T8 | Solution heat treated, cold worked, artificially aged |
| T9 | Solution heat treated, artificially aged, cold worked |
| T10 | Cooled from shaping, cold worked, artificially aged |
For extrusions, T4, T5 and T6 are by far the most common.
T5 — the workhorse of 6063
A T5 profile is quenched as it leaves the press (the extrusion process itself does the “solution” step) and then artificially aged in an oven. It is economical and ideal for 6063 architectural, LED, heat sink and framing profiles.
T6 — full strength
A T6 profile is solution heat treated so that alloying elements are fully dissolved, quenched quickly, then artificially aged. For quench-sensitive alloys such as 6061 and 6082 this usually needs a separate furnace or an intensive water quench. For 6063, a sufficiently fast press quench can reach T6 properties.
T4 — form first, age later
T4 material is solution treated and naturally aged: softer and more ductile. Profiles that must be bent or formed are often supplied in T4, formed, then artificially aged to T6.
T66 and other variants
EN 515 adds second digits for variants. T64 has lower strength than T6 for better formability; T66 reaches higher properties than T6 through special process control, and is common for 6060 and 6063 when a little more strength is needed without changing alloy.
Stress-relief suffixes
- TX510 — stress relieved by stretching, no further straightening.
- TX511 — stress relieved by stretching, minor straightening allowed. Example: 6061-T6511.
Stress relief keeps parts stable during heavy machining.
How temper is verified
On the shop floor, hardness tests (Webster or Vickers) quickly confirm that aging worked. Formal confirmation comes from tensile tests reported on the mill certificate. Ask for the certificate with your order.
Unsure which temper to specify? Tell us the loads and forming steps in your RFQ.
Frequently asked questions
Is 6063-T6 stronger than 6063-T5?
Yes. 6063-T6 reaches roughly 215 MPa minimum tensile strength versus about 175 MPa for T5 in typical standards, because the alloy is more completely solution treated before aging.
What does T6511 mean?
T6 plus stress relief by stretching (51), with minor straightening allowed after stretching (1). It is common for 6061 bar and profiles that will be machined.
Can the temper be changed after extrusion?
Yes, within limits. A profile can be solution heat treated and aged again to reach T6, or aged from T4 to T6 after forming. Welding locally reduces temper in the heat-affected zone.