Aluminum 2020-T651
Temper · default condition
AA 2020 · UNS A92020
T651 = t6, stress relieved by stretching
The historically standard plate condition: T6 strength with stretch stress-relief for dimensional stability after machining of skins and panels.
Values for the T651 condition
Other 2020 tempers and conditions
2020 is listed in 5 conditions; see the grade overview at 2020.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Soft interim condition for forming or machining before solution treatment; not a service temper. | 105 | 215 | 14 | 55 HB | 45 % IACS |
Solution heat treated and naturally aged | As-quenched/naturally aged interim state used only between quench and forming or artificial ageing; 2020 develops little strength without artificial ageing. | 235 | 370 | 10 | 100 HB | 30 % IACS |
Solution heat treated and artificially aged | Peak-strength, peak-stiffness condition for extrusions, sheet and forgings; use where static strength/modulus govern and toughness does not. | 525 | 580 | 5 | 150 HB | 33 % IACS |
T6, stress relieved by stretching, minor straightening | Extruded-shape equivalent of T651 where minor straightening after stretching is allowed; chosen for stiff stringers and spar caps. | 525 | 575 | 5 | 148 HB | 33 % IACS |
T651DefaultThis page T6, stress relieved by stretching | The historically standard plate condition: T6 strength with stretch stress-relief for dimensional stability after machining of skins and panels. | 530 | 580 | 4 | 150 HB | 33 % IACS |
What is 2020-T651?
2020-T651 is 2020 in the T651 temper — the historically standard plate condition: T6 strength with stretch stress-relief for dimensional stability after machining of skins and panels. 2020-T651 has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 580 MPa (84.1 ksi) — stronger than 97% of aluminum grades. Elongation at break is 4% and the elastic modulus is 76 GPa (11 Msi). 2020-T651 has a density of 2.8 g/cm³ (0.101 lb/in³), heavier than 81% of aluminum grades. It melts at 510°C (950 °F).
Advantages
- High strength — 530 MPa (76.9 ksi), better than 97% of aluminum grades
Limitations
- Needs corrosion protection — 28/100, worse than 99% of aluminum grades
- Difficult to weld — 15/100, worse than 96% of aluminum grades
2020-T651 properties
Typical room-temperature values for 2020-T651; 12 are specific to this condition. Other listed values are 2020 reference data and may not represent this condition. Bars are the position among aluminum grades.
Physical3
2020-T651 has a density of 2.8 g/cm³ (0.101 lb/in³), heavier than 81% of aluminum grades. It melts at 510°C (950 °F).
Mechanical11
2020-T651 has a yield strength of 530 MPa (76.9 ksi) and a tensile strength of 580 MPa (84.1 ksi) — stronger than 97% of aluminum grades. Elongation at break is 4% and the elastic modulus is 76 GPa (11 Msi).
Thermal6
2020-T651 is rated for continuous service to 150°C (302 °F). It conducts heat at 140 W/m·K (80.9 BTU/hr·ft·°F), worse than 52% of aluminum grades. Thermal expansion is 22.5 µm/m·K (12.5 µin/in·°F).
Electrical3
2020-T651 conducts electricity at 33 % IACS, worse than 57% of aluminum grades.
Chemical & Environmental3
Corrosion resistance is poor (28/100), worse than 99% of aluminum grades.
Sustainability4
Producing a kilogram of 2020-T651 takes about 205 MJ of energy and emits 13 kg of CO₂ — more than 76% of aluminum grades. Typical recycled content is 0%.
Manufacturability8
2020-T651's machinability is good (62/100, better than 55% of aluminum grades); weldability poor (15/100); formability poor (20/100).
Common Calculations5
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 2020-T651
Is 2020 easy to machine?
Machines like a hard 2000-series-T6 with good chip control, but the low ductility makes it notch-sensitive — use sharp carbide tools, generous radii and avoid sharp re-entrant corners.
Can 2020 be welded?
Effectively not fusion weldable: lithium causes oxide entrapment and porosity and the Cu-Li composition is hot-crack prone; joints were riveted or bonded, with FSW the only modern option.
Can 2020 be formed, bent or molded?
Form in the O or freshly quenched condition only; T6/T651 material has 3-6 % elongation and low short-transverse ductility, so cold bending and stretch forming of aged plate should be avoided.
What surface finishes work on 2020?
Clad, chromic-acid anodize or conversion-coat plus primer for corrosion protection; bare surfaces pit readily and sulphuric anodizing gives a dull grey film due to Cu and Li.
2020 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Cu | 4 – 5 | 4.5 |
| Liprincipal density-reducing / stiffness-raising addition | 0.9 – 1.7 | 1.2 |
| Mn | 0.3 – 0.8 | 0.5 |
| Cdageing accelerator; toxicity in melting was a major drawback | 0.1 – 0.3 | 0.2 |
| Siimpurity limit | ≤ 0.4 | — |
| Feimpurity limit | ≤ 0.4 | — |
| Others (each)total 0.15 max | ≤ 0.05 | — |
| Al | balance | — |
2020-T651 — frequently asked
What is 2020-T651 used for?
2020-T651 is typically used for historic aircraft skin panels, stiffness-critical airframe skins, aerospace research and comparison stock, legacy airframe repair and replacement plate, machined stiffeners and doublers on older airframes and test coupons for Al-Cu-Li property studies. In short: obsolete Al-Cu-Li skin alloy; high stiffness, low ductility; riveted or bonded only.
What is the yield strength of 2020-T651?
2020-T651 has a typical yield strength of 530 MPa (76.9 ksi) and a tensile strength of 580 MPa (84.1 ksi) — stronger than 97% of aluminum grades. Strength varies by condition: see the 5 listed tempers.
Is 2020-T651 easy to machine?
Reasonably — machinability is rated good (62/100, better than 55% of aluminum grades). Machines like a hard 2000-series-T6 with good chip control, but the low ductility makes it notch-sensitive — use sharp carbide tools, generous radii and avoid sharp re-entrant corners.
Can 2020-T651 be welded?
Not readily — weldability is rated poor (15/100). Effectively not fusion weldable: lithium causes oxide entrapment and porosity and the Cu-Li composition is hot-crack prone; joints were riveted or bonded, with FSW the only modern option.
What surface finishes work on 2020-T651?
Clad, chromic-acid anodize or conversion-coat plus primer for corrosion protection; bare surfaces pit readily and sulphuric anodizing gives a dull grey film due to Cu and Li.
Can 2020-T651 be formed, bent or molded?
Form in the O or freshly quenched condition only; T6/T651 material has 3-6 % elongation and low short-transverse ductility, so cold bending and stretch forming of aged plate should be avoided.
What is the maximum service temperature of 2020-T651?
2020-T651 is rated for continuous use to about 150°C (302 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 2020-T651 and 2020-O?
T651 is the default condition — the historically standard plate condition: T6 strength with stretch stress-relief for dimensional stability after machining of skins and panels. O: soft interim condition for forming or machining before solution treatment; not a service temper. Yield strength is 530 MPa in T651 versus 105 MPa in O.
Sources
- International Alloy Designations and Chemical Composition Limits for Wrought Aluminum (Teal Sheets) — The Aluminum Association (2018)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials — ASM International (1990)
- Aluminum-Lithium Alloys: Processing, Properties and Applications — Elsevier / Butterworth-Heinemann (2014)
- ASM Handbook Vol. 13B — Corrosion: Materials — ASM International (2005)
- MMPDS / MIL-HDBK-5 historical aluminum alloy data — Battelle / FAA (2022)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.