Last updated: June 22, 2026
Here's something that trips up a lot of first-time aluminum buyers. You've found the right alloy. 6061 or 6063. Price looks good. Then you see the temper column: T6, T5, H14, H32, O. And suddenly you're not sure what you're actually ordering.
I've seen importers pay a premium for 6061-T6 when they really needed 6063-T5 for a curtain wall project. And I've seen engineers spec T6 for a part that would have been fine — and cheaper — in T5. These are expensive mistakes. The alloy is only half the story. The temper is what gives the metal its real working properties.
This guide breaks down what O, H, T4, T5, T6, and other common tempers actually mean. Not the textbook definitions — what they mean for your project, your production line, and your budget.
What Is an Aluminum Temper?
A temper designation tells you how the aluminum was processed after casting. The base alloy chemistry is set at the mill. The temper is what happens next — heat treatment, strain hardening, or both.
The temper system follows ANSI H35.1 / ISO 2107 standards. Three main categories cover almost everything you'll encounter as an importer:
| Temper | Category | How It's Made | Strength Level |
|---|---|---|---|
| O | Annealed | Heated then slowly cooled | Lowest — fully softened |
| H | Strain-hardened | Cold worked (rolled, drawn) | Low to high (depends on number) |
| T | Heat-treated | Solution treated + aged | Medium to highest |
Non-heat-treatable alloys (1xxx, 3xxx, 5xxx series) use O and H tempers. Heat-treatable alloys (2xxx, 6xxx, 7xxx series) use T tempers. That's a simple rule but it gets overlooked more often than you'd think.
O Temper: Annealed (Softest)
O temper is the softest state. The metal is heated to recrystallization temperature and cooled slowly. No residual stress, maximum ductility.
Real-world use: Deep drawing, stamping, severe forming. If you're making a fuel tank or a complex pressed part, O temper is where you start.
Key properties of O temper:
- Lowest tensile and yield strength
- Highest elongation (formability)
- Best for bending, deep drawing, spinning
- Easy to work but easy to damage in handling
Most importers don't buy O temper directly. They buy H or T and form it. But knowing O temper is important because it's the baseline all other tempers build from.
H Temper: Strain-Hardened (Worked)
H tempers come from cold working — rolling, drawing, or stretching the metal after annealing. The more you work it, the harder it gets. Two digits follow the H:
- H1 — Strain-hardened only
- H2 — Strain-hardened then partially annealed
- H3 — Strain-hardened then stabilized (for alloys that age-soften)
- H4 — Strain-hardened then lacquered or painted
The second digit tells you how hard:
| Code | Hardness | Typical Elongation |
|---|---|---|
| H12 / H22 / H32 | 1/4 hard | 8–12% |
| H14 / H24 / H34 | 1/2 hard | 6–10% |
| H16 / H26 / H36 | 3/4 hard | 3–6% |
| H18 / H28 / H38 | Full hard | 1–4% |
Common examples importers buy:
- 5052-H32: Marine-grade plate, 1/4 hard, good for fuel tanks and saltwater environments. Tensile ~215 MPa.
- 3003-H14: General-purpose sheet, 1/2 hard, common for roofing and siding. Tensile ~150 MPa.
- 5083-H116: Special marine temper for shipbuilding. High corrosion resistance with good strength (~305 MPa).
T Temper: Heat-Treated (Strongest)
T tempers involve solution heat treatment followed by aging. This is where you get the real strength. The number after T tells you the specific processing path.
| Temper | Process | Typical Applications |
|---|---|---|
| T4 | Solution + natural aging (room temp) | Forming before final aging |
| T5 | Cooled from extrusion + artificial aging | Architectural extrusions (6063-T5) |
| T6 | Solution + artificial aging (full precipitation) | Structural parts (6061-T6, 7075-T6) |
| T651 | T6 + stress relieved by stretching | Machined plate, tooling |
6061-T6 vs 6063-T5: The Most Common Importer Decision
This is probably the single most common question I get from buyers. Here are real numbers:
| Property | 6061-T6 | 6063-T5 |
|---|---|---|
| Tensile Strength | 310 MPa | 185 MPa |
| Yield Strength | 276 MPa | 145 MPa |
| Elongation | 12% | 18% |
| Extrudability | Good | Excellent |
| Anodizing Quality | Good | Excellent |
| Surface Finish | Good | Excellent — uniform, minimal die lines |
| Relative Cost | Higher | Lower (~10–15% less) |
| Weldability | Excellent | Excellent |
| Typical Use | Structural frames, automotive, aerospace | Window frames, curtain walls, handrails, furniture |
I've seen fabricators in Southeast Asia order 6061-T6 for window frames because it sounds "stronger." But 6063-T5 extrudes cleaner, anodizes better, costs less, and has more than enough strength for non-load-bearing architectural profiles. The wrong temper choice here adds cost without adding value.
On the other hand, if you're building a structural frame that needs to carry load, 6063-T5's 145 MPa yield won't cut it. You need 6061-T6 at 276 MPa. Do the math before you order.
How to Read a Full Aluminum Alloy Spec
A complete spec has three parts. Example: 6061-T651
- 6 — Series (Al-Mg-Si, heat-treatable)
- 061 — Specific alloy within the series
- T651 — Temper: heat-treated, artificial aged, stress relieved by stretching
Another: 5052-H32
- 5 — Series (Al-Mg, non-heat-treatable)
- 052 — Specific alloy
- H32 — Temper: strain-hardened + stabilized, 1/4 hard
When you send an inquiry, always specify both alloy and temper. "6061" alone is not a complete spec. Neither is "T6." You need the full pairing.
Aluminum Temper Selection Checklist for Importers
Here's a practical checklist I use when advising buyers. Run through it before placing your order:
- Will the part be formed after cutting? (Yes → consider O or H12/H14; No → T5 or T6)
- Is it for an outdoor/architectural application? (Yes → prioritize extrudability and anodizing quality — 6063-T5)
- Does it need to bear load? (Yes → high-strength temper — 6061-T6 or 7075-T6)
- Will it be machined extensively? (Yes → T651 for stress-relieved plate, less warping)
- Is the environment marine or high-humidity? (Yes → H32/H116 temper on 5xxx series for corrosion resistance)
- Does the surface finish matter visually? (Yes → T5 over T6, or H temper with anodized finish)
- What's your tolerance for scrap? (Harder tempers = more springback, more tool wear)
- What certifications do you need? (Mill test certificates should list temper, not just alloy)
I keep a printed copy of this at my desk. Saves me from expensive phone calls later.
Common Temper Mistakes Importers Make
1. Ordering T6 when T5 would work. T6 costs more, is harder to extrude, and has a less uniform surface finish. If you don't need the extra strength, don't pay for it.
2. Confusing H14 and H32. Both are 1/2 hard (H14) and 1/4 hard (H32). But H32 is stabilized — it won't continue age-softening over time. For marine use, H32/H34 is the right call.
3. Assuming O temper is "standard." O temper is a specific, intentional soft state. If you order 5052-O and expect plate strength, you'll get something that bends under its own weight. Know what each temper does.
4. Overlooking T651 for machined parts. Regular T6 plate has internal stresses that release during machining. Parts warp. T651 has been stretched 1-3% to relieve those stresses. For any CNC work, T651 is worth the premium.
Quick Reference: Temper by Application
| Application | Recommended Temper | Why |
|---|---|---|
| Deep drawing, stamping | O | Maximum ductility, no cracking |
| General sheet metal | H14 | Good balance of strength and formability |
| Marine plate (5052/5083) | H32 / H116 | Corrosion resistance + stable strength |
| Window/door frames | 6063-T5 | Best extrudability and anodizing |
| Structural framing | 6061-T6 | High strength, good weldability |
| Handrails, furniture | 6063-T5 | Clean surface, cost-effective |
| CNC-machined parts | T651 | Stress-relieved, minimal warpage |
| Aerospace (high-stress) | 7075-T6 | Highest strength (572 MPa tensile) |
| Heat exchangers | 1050/1060 — O or H14 | High thermal conductivity |
| Roofing / cladding | 3003-H14 | Weather-resistant, economical |
Final Thoughts
I've been doing this long enough to know that most aluminum purchasing mistakes aren't about getting the wrong alloy. They're about getting the right alloy with the wrong temper. T6 vs T5. H14 vs H32. These differences cost real money and real time.
If you're not sure what temper you need, talk to us. We can walk through your application and help you spec it right the first time. We ship to ASTM B209, B210, B241, and GB/T 3880 standards — with mill certificates that list the full temper designation. For more on selecting the right aluminum grade, see our 5052 vs 6061 vs 7075 selection guide.
Get the temper right, and the rest is straightforward.