Anneal to O Temper (Aluminum)
Annealing & softening · Softening
Aluminum O-temper annealing removes strain hardening and produces the softest standard wrought condition.
Reference page — Aluminum O is not in the instant-quote configurator. Upload the part, name the treatment in the notes with the call-out below, and an engineer quotes it with the part.
Aluminum O at a glance
Four scores, each 0–100 against every heat treatment in this catalog. Hardness is derived from the HRC target (20 HRC = 0, 70 HRC = 100) — treatments without a hardness target (anneals, stress relief, HIP, cryo) are not rated. Toughness, dimensional stability and cost are FabDigit's engineering assessment.
What is Aluminum O?
Aluminum O-temper annealing removes strain hardening and produces the softest standard wrought condition. It is ordered before severe forming or when maximum ductility is more important than strength.
How it works
Cold-worked aluminum contains a high dislocation density and elongated grains. Heating into the alloy-specific recovery and recrystallization range forms new strain-free grains and removes most work hardening. Heat-treatable 2000 series, 6000 series, and 7000-series alloys can also change precipitate condition during a full anneal, so controlled heating and cooling are needed to reach a stable O temper rather than an unintended age-hardened state. Non-heat-treatable 1000 series, 3000 series, and 5000-series alloys soften primarily through recovery and recrystallization. Excess temperature or time causes grain growth and poor formed-surface appearance.
Why specify it
- Provides maximum ductility for deep drawing and tight bends
- Removes H-temper strain hardening
- Commonly reduces wrought aluminum to roughly 20–55 HB depending on alloy
Where it falls short
- Substantially lowers yield and tensile strength
- Some alloys can age naturally after thermal exposure
- Excessive grain growth can produce orange peel during forming
The Aluminum O cycle
Typical furnace parameters from the governing specifications and shop practice; the heat treater sets the exact recipe from the alloy, section size and required result.
| Temperature | 300–415 °C (572–779 °F) — Alloy-specific full-anneal range; use AMS 2770 or AMS 2772 tables. |
|---|---|
| Soak | 1–3 h — After load equalization; product thickness and alloy govern. |
| Cooling | Furnace cool |
| Atmosphere | Air |
| Door to door | 4–12 h — Controlled cooling can dominate heat-treatable-alloy cycles. |
Stages
- 1Heat uniformly to the alloy annealing range
- 2Soak after load equalization
- 3Cool at the specified rate to O temper
What Aluminum O does to the part
| Hardness | 20–55 HB — Representative O-temper range across common wrought aluminum alloys. |
|---|---|
| Section affected | The whole section transforms. |
| Tensile strength | 60–250 MPa — Broad O-temper range across 1000-series through 7000 series; use the material specification for acceptance. |
| Toughness | Ductility is maximized, although coarse recrystallized grains can reduce forming quality. |
| Distortion | Low risk. No quench is normally used, but thin sheet needs flat support and controlled cooling. |
| Surface after treatment | Air furnaces may discolor magnesium-bearing alloys; cleanliness prevents oil staining and eutectic melting contamination. |
| Machining sequence | Form in O temper, then solution treat and age if the final design requires a T temper. |
Specifications for Aluminum O
The documents a drawing cites to define this treatment. Each links to a page explaining the standard, its classes and the tests it invokes.
Test and related methods: ASTM E10 (Standard Test Method for Brinell Hardness of Metallic Materials), AMS 2750 (Pyrometry), ASTM B917 (Standard Practice for Heat Treatment of Aluminum-Alloy Castings from All Processes), ASTM B918 (Standard Practice for Heat Treatment of Wrought Aluminum Alloys).
Drawing call-out
ANNEAL 5052 SHEET TO O TEMPER PER AMS 2770; VERIFY TEMPER AND 47 HBW MAXIMUM PER ASTM E10 ON WITNESS COUPONWhich alloys take Aluminum O?
Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library. Typical grades: 1100-O, 3003-O, 5052-O, 6061-O, 2024-O, 7075-O.
| Material family | Verdict | Notes |
|---|---|---|
| Yes | Wrought aluminum is annealed to O temper using alloy- and product-specific AMS 2770 or AMS 2772 schedules.
| |
| No | Binder-jet aluminum does not use wrought O-temper processing. | |
| No | Brass requires lower-temperature stress relief or recrystallization annealing. | |
| No | Bronze requires composition-specific annealing or precipitation treatment. | |
| No | Cobalt-chrome requires alloy-specific solution or aging practice. | |
| No | Copper alloys require alloy-specific annealing or precipitation-hardening cycles. | |
| No | Printed aluminum does not receive a wrought-product O temper designation. | |
| No | Magnesium requires tightly controlled alloy-specific cycles. | |
| No | Nickel alloys require alloy-specific solution, anneal, or age cycles. | |
| No | Precious metals require alloy-specific annealing or age-hardening practice. | |
| No | Refractory metals require material-specific vacuum annealing practice. | |
| No | This cycle does not match the strengthening mechanism of the applicable stainless grade. | |
| No | This treatment cycle is not intended for the applicable steel transformation. | |
| No | Titanium requires alloy-specific annealing or solution-and-age cycles. | |
| No | Tungsten heavy alloys require supplier-specific sintering and stress-relief practice. | |
| No | Zinc alloys melt or lose properties at temperatures used by this process. |
Design rules for Aluminum O
What to decide on the drawing before the part goes to the heat treater.
- Identify the alloy designation and incoming condition on the purchase order.A temperature that is correct for one grade can overtemper, sensitize, or fail to transform another grade.
- Place hardness test locations at least 3 mm from an edge where geometry permits.Edge decarburization, local cooling, and indentation spacing can bias the reported result.
- Leave 0.2–0.5 mm finish stock on critical ground surfaces when a quench or scale-producing atmosphere is used.Final grinding removes oxide, decarburization, and dimensional movement after the thermal cycle.
- Allow 3–6 working days beyond machining.Furnace scheduling, controlled cooling, hardness testing, and certification extend beyond the soak time.
- Complete severe forming before any final T6 or T7 aging cycle.O temper has the highest available ductility, while age-hardened tempers crack at much larger bend radii.
Aluminum O versus the alternatives
Treatments engineers weigh against Aluminum O, and when each wins.
| Treatment | Hardness | Toughness | Stability | Cost | Choose it when |
|---|---|---|---|---|---|
Aluminum O this page | — | 95 | 85 | $$ | — |
| — | 75 | 95 | $ | when dimensional stability is needed without fully removing strain hardening | |
| 19 | 60 | 50 | $$ | when final strength is required after forming and solution treatment |
Cost, lead time and applications
Relative cost
Anneal to O Temper (Aluminum) is a standard-cost treatment ($$) relative to the other heat treatments in this catalog.
Heat treatment is priced per lot with a furnace minimum. The exact figure appears on the instant quote once the part is uploaded.
Lead time
| Added lead time | 3–6 working days |
|---|---|
| Furnace time | 4–12 h |
What Aluminum O is used for
- Deep-drawn aluminum shells
- Tight-radius sheet-metal bends
- Spun aluminum vessels
- Formed aircraft skins before final heat treatment
Aluminum O — frequently asked
What temperature is used for Aluminum O?
The representative process window is 300–415 °C, but the exact setpoint follows the alloy and governing specification. The listed soak is 1–3 h after the load reaches temperature.
What hardness does Aluminum O produce?
The catalog result is 20–55 HB. Hardness must be verified on the part or a qualified witness coupon using the test method called out on the drawing.
How long does Aluminum O take?
The thermal cycle is typically 4–12 h door to door. Commercial lead time is normally 3–6 additional working days because loading, certification, and inspection are separate from furnace time.
Will Aluminum O distort the part?
The catalog rates distortion risk as low. Reserve machining stock and verify critical datums after treatment when tolerances are tighter than 0.05 mm.
How should Aluminum O be specified on a drawing?
State the governing process specification, alloy condition, required result, and inspection location. Report hardness to ASTM E18 or ASTM E10 as applicable, and do not substitute a furnace recipe for an acceptance requirement.