Age T651 (Aluminum)
Solution treat & age · Precipitation hardening
Age T651 (Aluminum) is a precipitation-hardening condition for 6061 plate and 2024 plate and 7075 plate.
Al T651 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 Al T651?
Age T651 (Aluminum) is a precipitation-hardening condition for 6061 plate and 2024 plate and 7075 plate. It develops strength by solution treatment followed by controlled aging; the final condition, material specification, and acceptance test belong on the drawing.
How it works
Solution treatment dissolves strengthening constituents and establishes a controlled starting microstructure. Cooling retains a supersaturated or otherwise metastable matrix. During the prescribed age, diffusion forms a fine dispersion of strengthening precipitates that obstruct dislocation motion. Temperature and time control precipitate size, spacing, coherency, and grain-boundary chemistry: lower or shorter cycles generally favor peak strength, while overaging trades some strength for toughness, conductivity, or stress-corrosion resistance. The complete route, including the incoming material condition and cooling practice, is therefore part of the engineering definition.
Why specify it
- Produces 25–35 HRC across the stated grade set
- Provides 290 MPa or greater tensile capability where the cited product condition defines it
- Adds strength through precipitation rather than a carbon-steel temper
- Can be applied after near-net machining with less movement than a severe steel quench
Where it falls short
- Properties depend on alloy, product form, section size, and incoming condition
- Overaging or underaging can miss both strength and corrosion targets
- Solution treatment or quenching may distort thin and asymmetric parts
- A condition name does not replace material heat-lot traceability
The Al T651 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 | 115–190 °C (239–374 °F) — Primary solution or age temperature window represented by the stages; use the alloy-specific specification. |
|---|---|
| Soak | 4–24 h — At-temperature time; load and section corrections may apply. |
| Cooling | Still air |
| Atmosphere | Air |
| Door to door | 8–30 h — Typical furnace cycle excluding queue and laboratory testing. |
Stages
- 1Solution heat treat and quench to W temper
- 2Stress relieve by controlled stretching
- 3Artificially age to the T6 strength condition
What Al T651 does to the part
| Hardness | 25–35 HRC (80–150 HB) — Condition and product-form range; Brinell is commonly reported as 80–150 HB. |
|---|---|
| Section affected | The whole section transforms. |
| Tensile strength | 290–572 MPa — Strength follows the applicable alloy T6 product requirement; 6061-T651 is at least 290 MPa in common plate specifications. |
| Toughness | Comparable to T6 for the same alloy, with reduced residual stress rather than increased fracture toughness. |
| Distortion | Low risk. Controlled stretching after quench reduces plate residual stress and machining movement. |
| Surface after treatment | No intended surface change; protect from quench staining and handling damage. |
| Machining sequence | Preferred stock condition for extensive plate machining; machine symmetrically when possible. |
Specifications for Al T651
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 E18 (Standard Test Methods for Rockwell Hardness of Metallic Materials).
Drawing call-out
6061 PLATE, TEMPER T651 PER AMS 2770; TENSILE STRENGTH 290 MPa MIN; VERIFY HARDNESS PER ASTM E18Which alloys take Al T651?
Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library. Typical grades: 6061 plate, 2024 plate, 7075 plate.
| Material family | Verdict | Notes |
|---|---|---|
| Yes | Applicable to heat-treatable 2000 series, 6000 series, and 7000-series aluminum alloys as permitted by the product specification.
| |
| With care | Only for aluminum AM alloys with a qualified solution-and-age route.
| |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. | |
| No | This alloy category does not use the aluminum temper cycle. |
Design rules for Al T651
What to decide on the drawing before the part goes to the heat treater.
- Complete forming before artificial aging unless the product route expressly permits forming in temper.The precipitation response depends on the material condition entering the age cycle.
- Control quench delay and transfer time to preserve solution treatment response.Uniform temperature and controlled transfer reduce property variation and distortion.
- State the alloy, product specification, final condition, and hardness-test method on the drawing.A condition name alone does not define material pedigree or acceptance sampling.
- Protect finished dimensions and verify critical fits after treatment.Precipitation aging is low-distortion but can still produce measurable contraction or growth.
Al T651 versus the alternatives
Treatments engineers weigh against Al T651, and when each wins.
| Treatment | Hardness | Toughness | Stability | Cost | Choose it when |
|---|---|---|---|---|---|
Al T651 this page | 19 | 60 | 72 | $$ | — |
| 19 | 60 | 50 | $$ | when stress-relieved plate is not required | |
| 17 | 72 | 78 | $$$ | when SCC resistance is more important than peak strength |
Cost, lead time and applications
Relative cost
Age T651 (Aluminum) is a standard-cost treatment ($$) 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 | 3–7 working days |
|---|---|
| Furnace time | 8–30 h |
What Al T651 is used for
- Aerospace structural hardware
- Precision shafts, fittings, and actuators
- High-strength tooling and fixtures
- Corrosion-resistant mechanical components
Al T651 — frequently asked
What does Al T651 mean?
Al T651 identifies a controlled solution-treatment and precipitation-aging condition, not a generic furnace temper. The drawing should also identify the alloy specification and acceptance hardness or tensile requirement.
Is this a quench-and-temper treatment?
No in the metallurgical sense. Strength comes primarily from fine precipitates formed during aging rather than tempering quenched carbon-steel martensite.
Will the part distort?
The expected risk is low. Aging is normally more stable than a hard steel quench, but residual stress, section changes, fixtures, and prior solution treatment still matter.
How should hardness be verified?
Use ASTM E18 for Rockwell hardness on a suitable flat section. The expected catalog range is 25–35 HRC; thin sections may require ASTM E384 microindentation and an approved conversion.
Can the condition be assigned after machining?
Usually yes when the starting material and process route are compatible. The purchase order must preserve traceability to the governing product specification and the heat treater must certify the complete cycle.