Forging stock
Extruded or rolled bar supplied for customers who forge in-house, certified to the forging-stock specification.
Aerospace · Al-Mg forgings
5251 Aerospace Aluminium Forgings
5251 forgings are made from a 2 % magnesium aluminium alloy that cannot be heat treated, so they are chosen for fittings and housings that must resist corrosion and be welded, not for highly stressed parts. The traditional British forging-stock specification was L44. Metline supplies 5251 forging stock, open-die forgings and closed-die forgings to drawing, with full certification, to buyers worldwide.
- Alloy
- 5251 (Al-2Mg-0.3Mn)
- Condition
- As forged (H112) or annealed (O)
- Forms
- Forging stock, open- and closed-die parts
- Standards
- BS L44 (legacy) · EN 4400-6
When a 5251 forging makes sense
Most aerospace forgings are heat-treatable 2014, 2618, 6061, 7050 or 7075, because they give high strength after solution treatment and ageing. 5251 is different: its strength comes from magnesium in solid solution plus any cold work, and it stays essentially unchanged after welding.
That makes 5251 forgings useful for welded fittings in tanks and ducts, bosses and flanges joined to 5251 sheet or tube, corrosion-exposed housings, and parts for older British aircraft whose drawings call L44 forging stock. Forging also gives a sound, closed grain structure that follows the part outline, which helps fatigue and pressure tightness compared with machining from plate.
Designers should not expect high strength. As-forged 5251 typically gives tensile strength in the region of 160 – 200 MPa, roughly half that of 6061-T6. Where higher strength is needed in an Al-Mg forging, 5083 is the next step.
5251 composition (wt %)
| Element | Minimum | Maximum | Role in the alloy |
|---|---|---|---|
| Silicon (Si) | — | 0.40 | Impurity |
| Iron (Fe) | — | 0.50 | Impurity; affects grain size and surface |
| Copper (Cu) | — | 0.15 | Kept low to protect corrosion resistance |
| Manganese (Mn) | 0.10 | 0.50 | Adds strength and refines grain |
| Magnesium (Mg) | 1.7 | 2.4 | Main strengthening element (solid solution) |
| Chromium (Cr) | — | 0.15 | Grain control |
| Zinc (Zn) | — | 0.15 | Impurity |
| Titanium (Ti) | — | 0.15 | Grain refiner |
| Others, each / total | — | 0.05 / 0.15 | |
| Aluminium (Al) | Remainder | About 96.3 – 98.2 % |
Some published tables for "5251 forgings" list 2.2 – 2.8 % magnesium and tin limits; those values do not belong to 5251 and should not be used for acceptance.
Mechanical properties and test methods
Minimum properties for forgings depend on the specification, section thickness and test direction, and are normally agreed on the drawing or purchase order. The values below are indicative for as-forged material in moderate sections.
| Property | Indicative value | Notes |
|---|---|---|
| Tensile strength Rm | About 160 – 200 MPa | Higher in small, heavily worked sections |
| 0.2 % proof stress Rp0.2 | About 60 – 110 MPa | Annealed parts at the lower end |
| Elongation A | About 10 – 20 % | Depends on direction relative to grain flow |
| Hardness | About 45 – 60 HB | Used as a quick check on each part |
Tensile tests are taken from prolongations or sacrificial parts to EN ISO 6892-1 or ASTM B557. Aerospace orders may add ultrasonic inspection, macro-etch checks of grain flow and dye-penetrant inspection of finished surfaces.
Physical properties
- Density
- 2.69 g/cm³ (0.097 lb/in³)
- Modulus of elasticity
- About 70 GPa
- Thermal conductivity
- About 135 – 150 W/m·K
- Electrical conductivity
- About 35 – 37 % IACS
- Coefficient of thermal expansion
- About 24 µm/m·°C (20 – 100 °C)
- Melting range
- About 605 – 650 °C
Forging types and dimensional tolerances
Open-die forgings
Blocks, discs, rings and shafts forged between flat or simple dies and rough-machined. Suitable for one-off and low-volume parts.
Closed-die forgings
Near-net-shape parts produced in impression dies for repeat quantities, with less machining allowance.
Rolled rings
Seamless rings for flanges and adaptors, with grain flow running around the circumference.
| Feature | Typical tolerance (open-die / stock) |
|---|---|
| Diameter or thickness | Plus allowance only (for example +2 % / −0) to leave machining stock |
| Straightness | About 1.5 mm per metre |
| Twist | About 3 mm per metre |
| Surface | Free from cracks, laps and seams; burrs removed |
Final tolerances for closed-die parts follow the forging drawing or EN 586-3.
Typical uses and alternative alloys
- Welded fittings: bosses, ports and flanges welded into 5251 tanks and ducting
- Housings: corrosion-exposed covers, junction housings and brackets
- Legacy parts: replacement components for aircraft built to L44 drawings
- Ground equipment: forged lugs and fittings on welded GSE structures
| Need | Better choice | Why |
|---|---|---|
| More strength, still weldable | 5083 forging | About 4.5 % Mg gives roughly 50 % more strength |
| High strength, machined only | 6061-T6 or 6082-T6 forging | Heat-treatable; good corrosion resistance |
| Primary structure | 7050-T74 or 2014-T6 forging | Aerospace strength and toughness |
How to order 5251 forgings
- SpecifyAlloy and temper, forging drawing or envelope size, quantity and the governing specification with its revision (EN 4400-6, EN 586 or the forging drawing; L44 for legacy parts).
- ConfirmWe confirm the specification can be met, the tolerance class, any extra tests and the delivery terms (EXW, FOB, CIF or DAP).
- InspectMaterial is checked for dimensions and surface condition; tests named on the order are carried out or arranged with an independent laboratory.
- DocumentEach lot ships with a mill test certificate to EN 10204 3.1 showing chemistry and mechanical results, traceable to the cast or lot number.
- Pack and shipExport packing in sealed, moisture-protected wooden cases, crates or pallets, shipped by sea or air to your port or door.
References and standards
- BS EN 4400-6 – Aerospace series: aluminium alloy forging stock, technical specification
- BS 4L 44 – Forging stock of aluminium-magnesium alloy (withdrawn 1985)
- EN 586-3 – Aluminium and aluminium alloys: forgings, tolerances on dimension and form
- EN 573-3 – Aluminium and aluminium alloys: chemical composition and form of wrought products
- ASM Handbook, Vol. 2 – Properties and Selection: Nonferrous Alloys and Special-Purpose Materials
5251 aerospace aluminium (aluminum) forgings: FAQs
Can 5251 forgings be heat treated for higher strength?
No. 5251 is not heat treatable. Forgings are supplied as forged (H112) or annealed (O). For heat-treated strength choose 6061, 6082, 2014 or 7050.
Is L44 still a current specification?
BS 4L 44 was withdrawn in 1985, but legacy drawings still cite it. New procurement is normally written to EN 4400-6 plus agreed property requirements.
Why forge 5251 instead of machining from plate?
Forging closes porosity and aligns grain flow with the part shape, improving fatigue life and pressure tightness, and it reduces machining waste on larger parts.
Can 5251 forgings be welded to 5251 sheet?
Yes. TIG or MIG with ER5356 filler gives joints with near-parent strength and matched corrosion behaviour.
What inspection is available?
Dimensional checks, tensile and hardness tests, ultrasonic inspection, dye penetrant and grain-flow macro-etch can all be specified on the order.
Need a 5251 forging?
Send the drawing, quantity, specification and inspection requirements. We will reply with a forging route, certification and a delivered price.
