Aluminum 2018-O (Annealed)
Temper
AA 2018 · UNS A92018
Softest condition, used as intermediate stock for further forging, machining or straightening before heat treatment.
Values for the O condition
Other 2018 tempers and conditions
2018 is listed in 4 conditions; see the grade overview at 2018.
Compare all 4 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
OThis page Annealed | Softest condition, used as intermediate stock for further forging, machining or straightening before heat treatment. | 70 | 140 | 20 | 45 HB | 46 % IACS |
As fabricated | As-forged stock with no controlled thermal treatment; properties vary with section and are not guaranteed, used only as pre-machining blank. | 140 | 250 | 15 | 70 HB | 44 % IACS |
Solution heat treated and naturally aged | Intermediate condition after solution treatment; moderate strength with more ductility, normally aged on to T61 for service. | 205 | 350 | 18 | 95 HB | 33 % IACS |
T61Default T6 variant, underaged | The standard supply condition for 2018 forgings; best combination of elevated-temperature strength and dimensional stability for pistons and engine parts. | 315 | 420 | 12 | 120 HB | 40 % IACS |
What is 2018-O?
2018-O is 2018 in the O temper — softest condition, used as intermediate stock for further forging, machining or straightening before heat treatment. 2018-O has a yield strength of 70 MPa (10.2 ksi) and a tensile strength of 140 MPa (20.3 ksi) — weaker than 92% of aluminum grades. Elongation at break is 20% and the elastic modulus is 74 GPa (10.7 Msi). 2018-O has a density of 2.8 g/cm³ (0.101 lb/in³), heavier than 81% of aluminum grades. It melts at 507°C (945 °F). T61 is the default condition FabDigit quotes; O is available on request or by drawing note.
Advantages
- High service temperature — 200°C (392 °F), better than 90% of aluminum grades
- Ductile — tolerates forming and impact — 20%, better than 89% of aluminum grades
- High electrical conductivity — 46 % IACS, better than 87% of aluminum grades
- Conducts heat well — 172 W/m·K (99.4 BTU/hr·ft·°F), better than 84% of aluminum grades
- Forms and bends easily — 60/100, better than 77% of aluminum grades
Limitations
- Low strength — 70 MPa (10.2 ksi), worse than 92% of aluminum grades
- Difficult to weld — 22/100, worse than 83% of aluminum grades
- Needs corrosion protection — 38/100, worse than 79% of aluminum grades
2018-O properties
Typical room-temperature values for 2018-O; 10 are specific to this condition. Other listed values are 2018 reference data and may not represent this condition. Bars are the position among aluminum grades.
Physical3
2018-O has a density of 2.8 g/cm³ (0.101 lb/in³), heavier than 81% of aluminum grades. It melts at 507°C (945 °F).
Mechanical13
2018-O has a yield strength of 70 MPa (10.2 ksi) and a tensile strength of 140 MPa (20.3 ksi) — weaker than 92% of aluminum grades. Elongation at break is 20% and the elastic modulus is 74 GPa (10.7 Msi).
Thermal6
2018-O is rated for continuous service to 200°C (392 °F). It conducts heat at 172 W/m·K (99.4 BTU/hr·ft·°F), better than 84% of aluminum grades. Thermal expansion is 22.3 µm/m·K (12.4 µin/in·°F).
Electrical3
2018-O conducts electricity at 46 % IACS, better than 87% of aluminum grades.
Chemical & Environmental3
Corrosion resistance is fair (38/100), worse than 79% of aluminum grades.
Sustainability4
Producing a kilogram of 2018-O takes about 200 MJ of energy and emits 12.5 kg of CO₂ — less than 60% of aluminum grades. Typical recycled content is 20%.
Manufacturability6
2018-O's machinability is fair (45/100, worse than 72% of aluminum grades); weldability poor (22/100); formability good (60/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with 2018-O
Is 2018 easy to machine?
Machines well in T61 with carbide tooling, high speeds and light feeds; hard Ni/Fe intermetallics accelerate tool wear, so use flood coolant and sharp positive-rake geometry.
Can 2018 be welded?
Not recommended for fusion welding (severe hot cracking in Al-Cu); join by mechanical fasteners or, if unavoidable, resistance/friction-stir with post-weld solution treatment and re-aging.
Can 2018 be formed, bent or molded?
Primarily hot forged at ~400–450 °C; cold formability in T61 is poor — bend or straighten only in O or freshly solution-treated condition.
What surface finishes work on 2018?
Hard anodize for wear surfaces (dark, non-uniform color); chromate conversion or primer + paint recommended for corrosion protection; avoid decorative clear anodize.
2018 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 |
|---|---|---|
| Cuprincipal strengthener (Al₂Cu) | 3.5 – 4.5 | 4 |
| Nithermally stable Al-Cu-Ni intermetallics | 1.7 – 2.3 | 2 |
| Mg | 0.45 – 0.9 | 0.7 |
| Siimpurity limit | ≤ 0.9 | — |
| Feimpurity limit | ≤ 1 | — |
| Mn | ≤ 0.2 | — |
| Cr | ≤ 0.1 | — |
| Zn | ≤ 0.25 | — |
| Tigrain refiner | ≤ 0.15 | — |
| Others (each) | ≤ 0.05 | — |
| Others (total) | ≤ 0.15 | — |
| Al | balance | — |
2018-O — frequently asked
What is 2018-O used for?
2018-O is typically used for forged pistons, cylinder heads and aircraft engine parts. In short: hot-strength forging alloy; 200 °C service capability; legacy piston-alloy grade.
What is the yield strength of 2018-O?
2018-O has a typical yield strength of 70 MPa (10.2 ksi) and a tensile strength of 140 MPa (20.3 ksi) — weaker than 92% of aluminum grades. Strength varies by condition: see the 4 listed tempers.
Is 2018-O easy to machine?
Reasonably — machinability is rated fair (45/100, worse than 72% of aluminum grades). Machines well in T61 with carbide tooling, high speeds and light feeds; hard Ni/Fe intermetallics accelerate tool wear, so use flood coolant and sharp positive-rake geometry.
Can 2018-O be welded?
Not readily — weldability is rated poor (22/100). Not recommended for fusion welding (severe hot cracking in Al-Cu); join by mechanical fasteners or, if unavoidable, resistance/friction-stir with post-weld solution treatment and re-aging.
What surface finishes work on 2018-O?
Hard anodize for wear surfaces (dark, non-uniform color); chromate conversion or primer + paint recommended for corrosion protection; avoid decorative clear anodize.
Can 2018-O be formed, bent or molded?
Primarily hot forged at ~400–450 °C; cold formability in T61 is poor — bend or straighten only in O or freshly solution-treated condition.
What is the maximum service temperature of 2018-O?
2018-O is rated for continuous use to about 200°C (392 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between 2018-T61 and 2018-O?
T61 is the default condition — the standard supply condition for 2018 forgings; best combination of elevated-temperature strength and dimensional stability for pistons and engine parts. O: softest condition, used as intermediate stock for further forging, machining or straightening before heat treatment. Yield strength is 315 MPa in T61 versus 70 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: Properties and Physical Metallurgy (ed. J.E. Hatch) — ASM International (1984)
- ASTM B247 — Aluminum-Alloy Die, Hand and Rolled Ring Forgings — ASTM International (2020)
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.