F (as fabricated)
Extruded or rolled bar supplied for forging. The forger performs solution treatment and ageing after shaping the part. The most common condition for piston forging stock.
Heat-resistant aluminium bar and forging stock
2618 / 2618A Aluminium Bar and Rod
2618 and 2618A are aluminium-copper-magnesium-nickel-iron alloys designed to keep their strength at 150 – 250 °C, where most aluminium alloys soften. As bar, rod and forging stock they are used for forged pistons, compressor wheels, engine parts and airframe components that run hot. Metline supplies 2618 and 2618A round, square, flat and hex bar in the T6 and T8 family of tempers, certified to ASTM, AMS or EN, to customers worldwide.
- Alloy
- 2618 / 2618A (Al-Cu-Mg-Ni-Fe)
- Tempers
- F, O, T6, T61, T651, T6511, T851
- Service
- Strength retained to ~200 °C+
- Standards
- ASTM B221 · B247 · AMS 4132 · EN 755
What is 2618 aluminium?
2618 traces back to the British Hiduminium RR alloys developed for aero engines. In the 1960s it became famous as the main airframe alloy of Concorde (in its French form AU2GN, today 2618A), chosen because the skin of a Mach 2 aircraft runs at well over 100 °C for hours at a time.
The key is the combination of about 1 % iron and 1 % nickel. Together they form hard, thermally stable Al9FeNi intermetallic particles that do not dissolve or coarsen at operating temperature. Copper and magnesium provide precipitation hardening in the usual way, while the iron-nickel phase pins the structure and resists creep. The result is an alloy that is slightly less strong than 2014 or 2024 at room temperature but holds its strength far better after long exposure at 150 – 250 °C.
Today the largest single use of 2618 bar is as forging stock for high-performance pistons in motorsport, aviation and heavy-duty engines. It is also machined directly into turbocharger and compressor wheels, impellers, engine brackets and fittings near heat sources. Because it is a forging alloy at heart, bar is supplied in both as-fabricated (F) condition for forging and fully heat-treated tempers for direct machining.
2618 and 2618A chemical composition (wt %)
2618 is registered with the Aluminum Association and used in ASTM and AMS specifications; 2618A (AlCu2Mg1,5Ni) is the European designation in EN 573-3, with slightly wider limits. Both share the same metallurgical concept and are often dual-certified.
| Element | 2618 (AA / ASTM) | 2618A (EN 573-3) | Role |
|---|---|---|---|
| Silicon (Si) | 0.10 – 0.25 | 0.15 – 0.25 | Controlled; influences ageing |
| Iron (Fe) | 0.9 – 1.3 | 0.9 – 1.4 | Forms heat-stable Al-Fe-Ni particles |
| Copper (Cu) | 1.9 – 2.7 | 1.8 – 2.7 | Precipitation strengthening |
| Manganese (Mn) | — | 0.25 max | |
| Magnesium (Mg) | 1.3 – 1.8 | 1.2 – 1.8 | Precipitation strengthening with Cu |
| Nickel (Ni) | 0.9 – 1.2 | 0.8 – 1.4 | Forms Al9FeNi; key to heat resistance |
| Zinc (Zn) | 0.10 max | 0.15 max | Impurity |
| Titanium (Ti) | 0.04 – 0.10 | 0.20 max (Zr + Ti 0.25) | Grain refiner |
| Others, each / total | 0.05 / 0.15 | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder | Remainder |
Some older data sheets in circulation show 2618 with 2.4 – 3.5 % copper and about 2 % nickel. Those figures do not match the registered limits above; check any supplier data against EN 573-3 or the Aluminum Association registration before relying on it.
Mechanical properties of 2618 / 2618A
The figures below are typical values from Aluminum Association / ASM data for 2618-T61 forgings and published data for 2618A in T8 tempers. Specified minimums are lower and depend on product form and section size; for example, minimum values for EN AW-2618A extruded bar are set in EN 755-2. Design to the certified minimums.
| Temper / form | Tensile strength (typical) | Yield strength (typical) | Elongation | Hardness |
|---|---|---|---|---|
| 2618-T61 (forgings, bar) | 440 MPa / 64 ksi | 370 MPa / 54 ksi | 10 % | ≈115 HB |
| 2618A-T851 (stretched, aged) | ≈440 MPa | ≈410 MPa | ≈4 – 5 % | — |
| 2618A-T6 / T6511 (extruded bar) | about 400 – 440 MPa | about 330 – 420 MPa | ≈5 – 8 % | — |
What matters most for 2618 is behaviour after heat exposure. Where 2024-T3 or 2014-T6 lose a large share of their strength after prolonged time near 200 °C, 2618-T61 keeps markedly more of its tensile and creep strength. This is why piston designers accept its slightly lower room-temperature strength.
Physical properties (T61)
- Density
- about 2.76 g/cm³ (0.100 lb/in³)
- Melting range
- about 550 – 640 °C
- Modulus of elasticity
- about 74 GPa (10,700 ksi)
- Shear strength
- about 260 MPa (38 ksi)
- Fatigue strength (5×10⁸ cycles)
- about 125 MPa (18 ksi)
- Thermal conductivity
- about 146 – 150 W/m·K
- Electrical conductivity
- about 37 % IACS
- Coefficient of thermal expansion
- about 22 – 23 µm/m·°C (20 – 100 °C)
2618 tempers explained
O (annealed)
Softened for machining or forming operations before full heat treatment.
T6 / T61
Solution treated, quenched and artificially aged. T61 uses a quench and ageing practice developed for forgings; it is the standard condition in AMS 4132.
T651 / T6511
T6 with stress relief by stretching, for rolled (T651) or extruded (T6511) bar that will be machined.
T851 / T852
Cold worked or stretched before artificial ageing, giving higher yield strength. T852 applies to forgings stress-relieved by compression.
Choosing a temper
Order F for forging stock, T6511 or T851 for machining directly from bar, and T61 when your drawing references forging specifications.
2618 is not used in T3 or T4 naturally aged conditions for service; its benefits come from artificial ageing.
2618 standards and international equivalents
| System | Designation | Typical standards |
|---|---|---|
| Aluminum Association / ASTM | 2618 | ASTM B221 (extruded bar), ASTM B247 (die and hand forgings) |
| Aerospace (SAE) | 2618-T61 | AMS 4132 (die forgings and rolled rings) |
| UNS | A92618 | — |
| European (EN) | EN AW-2618A / AlCu2Mg1,5Ni | EN 573-3 (chemistry), EN 754-2 / EN 755-2 (bar), EN 586 (forgings) |
| German Werkstoff | 3.1924 | — |
| France (legacy NF) | AU2GN | AIR 9048 aerospace series |
| UK (legacy) | Hiduminium RR58 | DTD aerospace specifications |
| China (GB) | 2A70 / 2A80 (similar Al-Cu-Mg-Fe-Ni) | GB/T 3190 |
2A70 and 2A80 are related Chinese heat-resistant forging alloys with comparable chemistry, but they are not exact equivalents. When a drawing calls for 2618 or 2618A, certify to that designation.
2618 bar forms, sizes and weights
| Form | Typical range | Usual condition | Main use |
|---|---|---|---|
| Extruded round bar | From about 10 mm to large diameters | F, T6511, T851 | Forging stock, turned parts |
| Cast and homogenised billet / forged round | Large diameters for heavy forgings | F | Pistons and large forgings |
| Square and flat bar | Extruded or cut from plate | T6511, T851 | Machined brackets and fittings |
| Hex bar | Common across-flats sizes | T6511 | Fittings and nuts for hot environments |
| Saw-cut slugs | Cut to forging weight | F | Ready-to-forge piston blanks |
Weights for solid round 2618 bar at about 2.76 g/cm³:
| Diameter (mm) | kg per metre | 3 m bar (kg) | 6 m bar (kg) |
|---|---|---|---|
| 20 | 0.867 | 2.60 | 5.20 |
| 25 | 1.35 | 4.06 | 8.13 |
| 30 | 1.95 | 5.85 | 11.71 |
| 40 | 3.47 | 10.40 | 20.81 |
| 50 | 5.42 | 16.26 | 32.52 |
| 60 | 7.80 | 23.41 | 46.82 |
| 70 | 10.62 | 31.87 | 63.73 |
| 80 | 13.87 | 41.62 | 83.24 |
| 90 | 17.56 | 52.68 | 105.35 |
| 100 | 21.68 | 65.03 | 130.06 |
| 120 | 31.21 | 93.64 | 187.29 |
| 150 | 48.77 | 146.32 | 292.64 |
| 200 | 86.71 | 260.12 | 520.25 |
Forging, heat treatment, machining and joining
Forging
Excellent hot workability. Forge in the region of 410 – 450 °C, keeping dies hot to avoid surface cracking. Grain flow should follow the part profile, especially in piston crowns and pin bosses.
Heat treatment
Solution treat at about 525 – 535 °C, quench (often in hot or boiling water for forgings to limit distortion), then age at around 190 – 200 °C. Follow AMS 2770 or the forging specification.
Machining
Machines well in aged tempers, with short chips and a good finish. Hard Al-Fe-Ni particles are abrasive, so carbide or PCD tools last much longer than HSS.
Welding
Not recommended for fusion welding; the alloy is prone to hot cracking. Use mechanical joining. Friction welding is possible in some designs.
Corrosion
Fair. Parts are usually anodised or coated for corrosive environments; pistons operate in oil and need no special protection.
Surface treatments
Hard anodising of ring grooves and skirt coatings are common on pistons to improve wear resistance.
2618 versus 4032 for forged pistons
Forged piston makers mainly choose between 2618 and 4032. The decision comes down to the trade-off between toughness and thermal expansion.
| Factor | 2618 / 2618A | 4032 |
|---|---|---|
| Silicon content | Very low (≈0.2 %) | High (≈12 %) |
| Thermal expansion | Higher (≈22 – 23 µm/m·°C) | Lower (≈19 – 20 µm/m·°C) |
| Piston-to-bore clearance | Larger; some cold-start noise | Tighter; quieter running |
| Toughness and ductility | Higher; tolerant of detonation and boost | Lower; less forgiving of abuse |
| Strength at high temperature | Excellent | Good |
| Wear resistance | Good (often coated) | Very good (silicon particles) |
| Typical use | Racing, turbo, nitrous and heavy-duty engines | Street performance and endurance pistons |
In short, 2618 is the choice when the engine is pushed hard and reliability under extreme loads matters more than noise; 4032 suits engines that need tight clearances and long, quiet service.
Where 2618 bar and forgings are used
- Engines: forged pistons for motorsport, aviation, marine and heavy-duty diesel engines
- Turbomachinery: compressor wheels, impellers and blower rotors
- Aerospace: airframe skins and structure for supersonic aircraft, engine mounts and hot-section fittings
- Automotive: connecting rods, cylinder head and valvetrain parts in performance engines
- Defence: parts that must retain strength after heat exposure
- Industrial: fittings and machine parts operating continuously at 150 – 230 °C
2618 compared with 2024, 7075, 2219 and 6061
| Property | 2618-T61 | 2024-T351 | 7075-T6 | 2219-T851 | 6061-T6 |
|---|---|---|---|---|---|
| Typical tensile strength (RT) | 440 MPa | 469 MPa | 572 MPa | 455 MPa | 310 MPa |
| Strength retention at 200 °C | Very good | Fair | Poor | Very good | Poor |
| Creep resistance | Very good | Fair | Poor | Very good | Poor |
| Forgeability | Excellent | Good | Good | Good | Excellent |
| Fusion weldability | Poor | Poor | Poor | Good | Good |
Choose 2618 for unwelded parts that run hot. If the part must also be fusion welded, look at 2219; if it runs at room temperature, 2024 or 7075 offer more strength.
How to order 2618 / 2618A bar from Metline
- SpecifyAlloy (2618 or 2618A), temper (F for forging stock, or T6511 / T851 / T61), diameter or section, length or slug weight, and quantity.
- Confirm the standardASTM B221 or B247, AMS 4132, or EN 755-2 / EN 586, plus any customer or aerospace specification and ultrasonic class.
- QuoteWe confirm availability, tolerance class, certification and delivery terms (EXW, FOB, CIF or DAP) for your destination port or site.
- Process and inspectBar is cut to length or slug weight, checked for size and surface, and ultrasonically tested where the order requires it.
- Document and shipEach lot ships with an EN 10204 3.1 mill test certificate and packing list. Bars are bundled or cased in seaworthy wooden boxes with moisture protection; third-party inspection can be arranged on request.
References and standards
- SAE AMS 4132 – Aluminum Alloy Die Forgings and Rolled Rings, 2618-T61
- ASTM B247 – Aluminum and Aluminum-Alloy Die Forgings, Hand Forgings, and Rolled Ring Forgings
- EN 573-3 – Chemical composition and form of wrought products (EN AW-2618A)
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits (Teal Sheets)
- ASM Handbook, Vol. 2 – Properties of Wrought Aluminum and Aluminum Alloys: 2618
2618 aluminium (aluminum) bar: frequently asked questions
What is the difference between 2618 and 2618A?
2618 is the Aluminum Association / ASTM registration; 2618A is the European EN 573-3 version (AlCu2Mg1,5Ni) with slightly wider limits on copper, nickel, iron and titanium plus a manganese limit. They behave almost identically and are frequently dual-certified.
Why is 2618 used for racing pistons?
It keeps strength at high temperature, resists creep and is tough enough to survive detonation and high boost. Its higher thermal expansion means larger cold clearances, which racing engines accept.
What temperature can 2618 aluminium handle?
It is designed for sustained service around 150 – 230 °C, with better strength retention in that range than 2014, 2024 or 7075. Above about 250 °C all aluminium alloys lose strength quickly.
Can 2618 be welded?
Fusion welding is not recommended because of hot-cracking sensitivity. Design for mechanical joints; for a weldable heat-resistant alloy, consider 2219.
Should I order 2618 bar in F or T6 temper?
Order F (as fabricated) if the bar will be forged, because the part is heat treated after forging. Order T6511, T651 or T851 if you will machine parts directly from bar.
What is the density of 2618?
About 2.76 g/cm³. A 100 mm round bar weighs roughly 21.7 kg per metre.
Need 2618 or 2618A bar?
Send alloy, temper, size, quantity and specification. Our team will reply with availability, certification and delivered terms.
