Aluminum Alloy and Temper Guide for Coil Coating.
An alloy number describes the chemistry. Temper describes the condition that chemistry was left in after rolling. A coil coating spec needs both, and it is the second one people forget to write down.
Key takeaways
- Alloy chemistry sets the ceiling on strength and corrosion resistance; temper sets where the coil actually sits under that ceiling.
- O (annealed) is softest and most formable; H-series tempers trade formability for strength, with the first digit indicating treatment type and the second the degree of hardening.
- H3 stabilization applies specifically to magnesium-bearing alloys like 5xxx, which age-soften at room temperature without it.
- A softer temper bends to a tighter radius before cracking; a harder temper needs a larger minimum bend radius for the same operation.
- A complete coil coating line item states alloy, temper, gauge, width and coating system together, not alloy alone.
Why does temper matter as much as the alloy number?
Because two coils of the same alloy, say 3003 or 5052, can behave quite differently depending on temper. Alloy chemistry sets the ceiling on what the metal can do; temper sets where the coil actually sits under that ceiling when it arrives at your line, in strength, formability and how much further cold work it can take before cracking.
Ordering aluminum alloy sheet metal for a coil coating program by alloy number alone, without stating temper, leaves that decision to whoever happens to be running the mill order, which is not where you want it made.
What do the O, H and F temper letters actually mean?
O is annealed, the softest and most formable condition with the lowest strength, used where the forming operation is severe. H-series is strain hardened, with strength built in through cold work during rolling. F is as-fabricated, with no special control over the process, and rarely what a coil coating spec should call for.
- O (annealed). Softest, most formable, lowest strength. Used where cracking risk needs to be minimized on a severe forming operation.
- H-series (strain hardened). The first digit after the H indicates the treatment: H1 is strain hardened only, H2 is strain hardened then partially annealed back down to the target strength, and H3 is strain hardened then stabilized against further age-softening, which applies specifically to magnesium-bearing alloys such as the 5xxx series. The second digit, 1 through 9, indicates how much strain hardening was applied: higher generally means more strength and less formability.
- F (as fabricated). No special control over the thermal or strain-hardening condition. Properties are not guaranteed.
Heat-treatable alloys carry a separate set of T-series tempers, but since Orbit's coil coating program runs on non-heat-treatable 1xxx, 3xxx and 5xxx alloys, the H-series and O temper are what most of Orbit's coil specifications need to get right. The temper designation system is defined by the Aluminum Association's own ANSI H35.1/H35.1M standard.
Is the softest temper always the safest default?
No. It is tempting to default to O temper on the assumption that the softest, most formable condition removes risk, but that trades one risk for another: a fully annealed panel has lower strength and is generally more susceptible to denting during handling, transport and installation than a harder H-series temper.
Where a project genuinely needs the tightest possible forming, O temper earns its place. Where the forming operation is moderate, a lighter H-series temper often gives a better balance of formability during fabrication and dent resistance afterward. The right answer depends on the specific bend the profile requires, not on defaulting to either end of the range.
How does temper interact with forming radius?
A softer temper bends around a tighter radius before the outer surface strains enough to crack. A harder temper holds a flatter panel and resists denting better, but needs a larger bend radius for the same operation. This is a general principle of sheet metal behavior across alloys, not an Orbit-specific claim.
The radius a given alloy, temper and gauge combination can actually run is confirmed against your specification rather than assumed from the temper letter alone. Coating adds a second constraint on top of the metal: whether the coil is coated before or after forming changes what "safe radius" means, since a coating that flexes fine on a flat pan can craze at a tight bend if it was not selected with that forming operation in mind. Tell us the tightest bend radius in your profile along with the temper you are considering, and we will confirm both together.
Does temper affect how the coil comes through the coating line?
Yes, favorably for non-heat-treatable alloys. Because 1xxx, 3xxx and 5xxx alloys are non-heat-treatable, their strength is locked in by rolling and does not depend on a later thermal step, so the bake cycle on a coating line generally disturbs a non-heat-treatable alloy's temper far less than it does a heat-treatable alloy's, though the specific outcome still depends on alloy, temper, peak metal temperature and dwell time.
That is a meaningful advantage over heat-treatable alloys, whose properties can be more sensitive to the thermal history a coating line's bake oven introduces. Orbit runs PE, HDPE, PVDF, PU, PUPA, Epoxy, Acrylic and Epoxy-PE across the alloy and temper ranges its rolling program covers, with the coating system and finish chosen against the application rather than fixed to one alloy.
How do I make sure the coil I receive matches the temper I ordered?
Check the mill certificate against the specification, not just the purchase order. When coil ships, the mill certificate documents the alloy and temper actually supplied, along with gauge and width, and it is worth confirming that certificate matches what was specified rather than assuming the two automatically align.
This matters most on long-running projects or repeat orders, where a later batch can drift from the original temper if the requirement was not stated precisely the first time. Keeping alloy and temper explicit in the purchase order, not just in an early conversation, is the simplest way to avoid that drift.
What should a complete coil coating line item include?
Alloy, temper, gauge, width and coating system, stated together, not alloy alone. If temper is left open, say so explicitly and describe the forming operation instead, and let the mill propose a temper that fits it.
For background on how the alloy series itself is chosen before temper enters the conversation, see our guide to the 1xxx, 3xxx and 5xxx series. For how gauge, alloy and temper come together specifically for roll-formed roofing and cladding profiles, see aluminum coil gauge and alloy selection for roll forming and roofing. Specific mechanical property values for a given alloy and temper combination are available on request against your specification.
How do the common tempers compare at a glance?
| Temper | Treatment | Relative strength | Relative formability |
|---|---|---|---|
| O | Annealed | Lowest | Highest |
| H1x | Strain hardened only | Increases with second digit | Decreases with second digit |
| H2x | Strain hardened, partially annealed | Increases with second digit | Decreases with second digit |
| H3x | Strain hardened, stabilized (magnesium alloys) | Increases with second digit | Decreases with second digit |
| F | As fabricated, uncontrolled | Not guaranteed | Not guaranteed |
Common questions
What temper should I specify if I don't know yet?
Describe the forming operation instead of naming a temper by habit, and we will propose one that fits it. Stating the tightest bend radius the profile requires is more useful to us than guessing at an H-number.
Can I mix tempers within one order?
That depends on the application. Different parts of a project sometimes call for different tempers of the same alloy. Tell us the forming requirement for each part and we will confirm what is workable.
Does Orbit publish tensile and yield values by temper?
Specific mechanical property values for a given alloy, temper and gauge combination are available on request against your specification, since the applicable figures depend on gauge and temper together.
What happens if temper isn't stated on my purchase order?
It leaves the decision to whoever is running the mill order. Stating alloy and temper explicitly in the purchase order, not just in an earlier conversation, is the simplest way to avoid drift on repeat orders.
Do heat-treatable alloys use the same temper letters?
No. Heat-treatable alloys carry a separate T-series (such as T6). Orbit's rolling program is non-heat-treatable 1xxx, 3xxx and 5xxx, so the O and H-series tempers covered here are what apply.
References
Specifying alloy and temper for a coil program?
Send your application, forming requirement, coating and gauge. We will confirm the alloy and temper combination and respond within one business day.