Aluminum 2139-T851
Temper
AA 2139 · UNS A92139
T851 = t8, stress relieved by stretching
Choose for thick plate that will be heavily machined — stretch stress relief minimises distortion of machined structural parts.
Values for the T851 condition
Other 2139 tempers and conditions
2139 is listed in 6 conditions; see the grade overview at 2139.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Annealed | Softest condition for severe forming or intermediate processing; must be re-heat-treated to reach strength. | 85 | 195 | 18 | 50 HB | 47 % IACS |
Solution heat treated and naturally aged | Use when moderate strength with better ductility is needed, or as the condition for forming before artificial ageing. | 275 | 430 | 20 | 115 HB | 30 % IACS |
Solution heat treated, cold worked and naturally aged | Naturally aged plate/sheet condition when high toughness and formability matter more than peak yield strength. | 315 | 455 | 17 | 125 HB | 30 % IACS |
Solution heat treated and artificially aged | Peak-aged without prior stretching — used for forgings and machined parts where residual stress control is by machining strategy. | 415 | 470 | 9 | 130 HB | 36 % IACS |
T851This page T8, stress relieved by stretching | Choose for thick plate that will be heavily machined — stretch stress relief minimises distortion of machined structural parts. | 448 | 480 | 10 | 134 HB | 38 % IACS |
T8Default Solution heat treated, cold worked and artificially aged | The standard supply condition: best combination of strength, fracture toughness and fatigue crack growth resistance for fuselage and armour plate. | 450 | 485 | 11 | 135 HB | 37 % IACS |
What is 2139-T851?
2139-T851 is 2139 in the T851 temper — choose for thick plate that will be heavily machined — stretch stress relief minimises distortion of machined structural parts. 2139-T851 has a yield strength of 448 MPa (65 ksi) and a tensile strength of 480 MPa (69.6 ksi) — stronger than 91% of aluminum grades. Elongation at break is 10% and the elastic modulus is 72 GPa (10.4 Msi). 2139-T851 has a density of 2.85 g/cm³ (0.103 lb/in³), heavier than 96% of aluminum grades. It melts at 507°C (945 °F). T8 is the default condition FabDigit quotes; T851 is available on request or by drawing note.
Advantages
- Tough — resists crack growth — 46 MPa·√m (41.9 ksi·√in), better than 100% of aluminum grades
- High strength — 448 MPa (65 ksi), better than 91% of aluminum grades
- Easy to machine — 74/100, better than 85% of aluminum grades
Limitations
- Needs corrosion protection — 32/100, worse than 94% of aluminum grades
- Difficult to weld — 20/100, worse than 89% of aluminum grades
2139-T851 properties
Typical room-temperature values for 2139-T851; 12 are specific to this condition. Other listed values are 2139 reference data and may not represent this condition. Bars are the position among aluminum grades.
Physical3
2139-T851 has a density of 2.85 g/cm³ (0.103 lb/in³), heavier than 96% of aluminum grades. It melts at 507°C (945 °F).
Mechanical12
2139-T851 has a yield strength of 448 MPa (65 ksi) and a tensile strength of 480 MPa (69.6 ksi) — stronger than 91% of aluminum grades. Elongation at break is 10% and the elastic modulus is 72 GPa (10.4 Msi).
Thermal6
2139-T851 is rated for continuous service to 150°C (302 °F). It conducts heat at 152 W/m·K (87.8 BTU/hr·ft·°F), better than 66% of aluminum grades. Thermal expansion is 22.7 µm/m·K (12.6 µin/in·°F).
Electrical3
2139-T851 conducts electricity at 38 % IACS, better than 61% of aluminum grades.
Chemical & Environmental3
Corrosion resistance is poor (32/100), worse than 94% of aluminum grades.
Sustainability4
Producing a kilogram of 2139-T851 takes about 205 MJ of energy and emits 12.5 kg of CO₂ — more than 76% of aluminum grades. Typical recycled content is 12%.
Manufacturability8
2139-T851's machinability is very good (74/100, better than 85% of aluminum grades); weldability poor (20/100); formability poor (22/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 2139-T851
Is 2139 easy to machine?
Machines well in T8 with sharp carbide tooling, high speeds and flood coolant; low Fe/Si content gives clean surfaces, and stretch-relieved T851 plate is preferred for deep pocket milling to limit distortion.
Can 2139 be welded?
Not suitable for fusion (GTAW/GMAW) welding — hot cracking and toughness loss; join by riveting/bolting or use friction stir welding, which retains most base-metal properties.
Can 2139 be formed, bent or molded?
Form in O or T4/T3 condition; T8 plate has limited bend ductility and needs generous radii, warm forming or age-forming for contoured skins.
What surface finishes work on 2139?
Chromic or boric-sulphuric anodize plus epoxy primer, or Alclad/spray-coat protection; bare Cu-rich surfaces pit in chlorides, and cosmetic sulphuric anodize gives grey, non-uniform colour.
2139 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 – 5.5 | 5 |
| Mg | 0.2 – 0.8 | 0.5 |
| Agkey micro-alloying addition (Ω-phase former) | 0.15 – 0.6 | 0.4 |
| Mn | 0.2 – 0.6 | 0.3 |
| Siimpurity limit for toughness | ≤ 0.1 | — |
| Feimpurity limit for toughness | ≤ 0.15 | — |
| Zn | ≤ 0.25 | — |
| Ti | ≤ 0.15 | — |
| Others (each)others total 0.15 max | ≤ 0.05 | — |
| Al | balance | — |
2139-T851 — frequently asked
What is 2139-T851 used for?
2139-T851 is typically used for fuselage plate, pressure bulkheads, machined skin panels with integral stiffeners, armor and blast-resistant structural plate, wing and fuselage frames and damage-tolerant structural fittings. In short: silver-modified Al-Cu plate; best machinability in group; damage-tolerant fuselage alloy.
What is the yield strength of 2139-T851?
2139-T851 has a typical yield strength of 448 MPa (65 ksi) and a tensile strength of 480 MPa (69.6 ksi) — stronger than 91% of aluminum grades. Strength varies by condition: see the 6 listed tempers.
Is 2139-T851 easy to machine?
Yes — machinability is rated very good (74/100, better than 85% of aluminum grades). Machines well in T8 with sharp carbide tooling, high speeds and flood coolant; low Fe/Si content gives clean surfaces, and stretch-relieved T851 plate is preferred for deep pocket milling to limit distortion.
Can 2139-T851 be welded?
Not readily — weldability is rated poor (20/100). Not suitable for fusion (GTAW/GMAW) welding — hot cracking and toughness loss; join by riveting/bolting or use friction stir welding, which retains most base-metal properties.
What surface finishes work on 2139-T851?
Chromic or boric-sulphuric anodize plus epoxy primer, or Alclad/spray-coat protection; bare Cu-rich surfaces pit in chlorides, and cosmetic sulphuric anodize gives grey, non-uniform colour.
Can 2139-T851 be formed, bent or molded?
Form in O or T4/T3 condition; T8 plate has limited bend ductility and needs generous radii, warm forming or age-forming for contoured skins.
What is the maximum service temperature of 2139-T851?
2139-T851 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 2139-T8 and 2139-O?
T8 is the default condition — the standard supply condition: best combination of strength, fracture toughness and fatigue crack growth resistance for fuselage and armour plate. O: softest condition for severe forming or intermediate processing; must be re-heat-treated to reach strength. Yield strength is 450 MPa in T8 versus 85 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 — ASM International (1990)
- MMPDS-style typical property data for 2000-series aerospace plate — Battelle/FAA (2023)
- 2139-T8 high-toughness aluminium plate data (Al-Cu-Mg-Ag) — Alcoa/Constellium (aerospace plate producers) (2016)
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.