Large-Size Aluminium Forgings: Rings, Shafts, Discs & Blocks
Large aluminium forgings are open-die blocks, seamless rolled rings, shafts, discs and custom shapes worked from cast ingot under a press or hammer, so that the metal is dense and its grain follows the part. They are specified where a part is too big, too highly stressed or too safety-critical for plate, extrusion, casting or a welded build-up. This guide explains the forms, alloys, tempers, size limits and inspection that matter when you buy them.
- Forms
- Rings, shafts, discs, blocks, hollows, custom shapes
- Alloys
- 6061, 2014, 2219, 7050, 7075, 5083
- Tempers
- T6, T652, T73, T7452, H112
- Standards
- ASTM B247 · EN 586 · AMS
What counts as a large aluminium forging?
There is no formal size threshold, but in purchasing practice a forging is "large" when it needs a heavy hydraulic press or ring mill, weighs hundreds of kilograms to several tonnes, or has a section thick enough that quenching and through-hardening become the main engineering problem. Typical examples are bearing rings over a metre in diameter, flanged shafts several metres long and blocks thicker than the thickest available rolled plate.
Forging improves on the cast ingot in three ways. The hot working closes internal porosity and breaks up the coarse cast structure; the grain is elongated in the direction of metal flow, so strength, ductility and fatigue resistance are highest along the main load path; and because the shape is formed close to the final part, less metal is machined away than when the same component is hogged from a block of plate.
The trade-off is that large forgings are made one at a time or in small lots, need careful heat treatment and are fully inspected. That makes them more expensive per kilogram than plate or extrusion, so the choice should be based on what the part actually requires: size, integrity, directional properties or all three.
Large forging types and where each is used
Seamless rolled rings
A pierced and upset pancake is expanded on a radial-axial ring mill. Grain runs circumferentially, which suits slewing and bearing rings, flanges, tank interface rings, gear blanks and turbine casings. Rolled rings are the most material-efficient way to make large-diameter, relatively thin-walled annular parts.
Shafts (solid, hollow, stepped)
Drawn out between flat or swage dies along the axis, often with integral flanges or steps. Used for drive spindles, hydraulic cylinder rods, rollers and landing-gear and actuator members where axial grain improves fatigue life.
Discs and flanges
Upset from a billet so grain runs radially. Used for wheel and hub blanks, end covers, impeller and coupling blanks, vacuum flanges and large valve bodies.
Blocks and slabs
Open-die forged in two or three directions to give more uniform properties than very thick rolled plate. Used for mould bases, machine beds, structural fittings and frames machined from solid.
Hollows and thick-wall pipe
Forged over a mandrel or produced as tall rings for pressure housings, thick nozzles and heavy pipe fittings where seamless construction is required.
Custom and stepped shapes
Open-die forgings with offsets, bosses or tapered sections, or closed-die forgings where quantity justifies tooling. The forged envelope is designed to leave a sensible machining allowance on every face.
Which alloy and temper for a large forging?
Alloy choice for heavy forgings is driven as much by quench sensitivity as by strength. A thin forging cools quickly in the quench tank and reaches full properties throughout; the centre of a 300 mm section cools far more slowly, and alloys that are quench sensitive lose strength there. Low-quench-sensitivity alloys such as 7050 were developed precisely for thick sections.
| Alloy | Typical tempers | Character | Typical large parts |
|---|---|---|---|
| 6061 | T6, T652 | Medium strength, good corrosion resistance, weldable, anodises well | Flanges, rings, vacuum and semiconductor chambers, marine and general engineering parts |
| 6082 | T6, T652 | European counterpart to 6061, slightly stronger in thick sections | Structural rings, machine components, rail and transport parts |
| 2014 | T6, T652 | High strength, good machinability; needs corrosion protection | Heavy-duty fittings, wheels, hydraulic and machinery components |
| 2219 | T6, T852 | Weldable, keeps strength at elevated and cryogenic temperatures | Rocket and cryogenic tank rings, Y-rings and domes, hot structural parts |
| 2618 | T61 | Creep resistant at elevated temperature | Compressor and engine components, high-temperature rings |
| 7075 | T6, T652, T73, T7352 | Very high strength; T73 gives much better stress-corrosion resistance | Highly stressed fittings, moulds, defence and aerospace parts in moderate sections |
| 7050 | T74, T7452 | High strength with low quench sensitivity and good toughness | Thick aerospace bulkheads, frames, landing-gear and wing fittings |
| 5083 | H112, O | Non-heat-treatable, excellent seawater and cryogenic performance | Marine flanges, LNG and cryogenic fittings |
Temper designations ending in 52 (T652, T7352, T7452) mean the forging was stress-relieved by a controlled cold compression of roughly 1 – 5 % after quenching. For large forgings that will be heavily machined this is important: without it, residual quench stresses cause the part to move as metal is removed. The T73 and T74 over-aged tempers of 7xxx alloys sacrifice some strength for resistance to stress-corrosion cracking, which is usually the governing failure mode in thick 7xxx parts loaded in the short-transverse direction.
Minimum mechanical properties for forgings depend on alloy, temper, forging type, thickness and test direction (longitudinal, long-transverse or short-transverse). They are set out in the tables of ASTM B247, EN 586-2 and the relevant AMS specification and are reported on the certificate for each heat-treat lot.
What determines how big an aluminium forging can be?
Buyers often ask for a single maximum size, but the practical limit is set by a chain of equipment and metallurgy, and the weakest link decides. When you send a drawing, these are the questions a forging engineer checks:
| Limiting factor | Why it matters |
|---|---|
| Ingot size and quality | The forging can never weigh more than the ingot minus crop and machining losses. Large direct-chill ingots must be free of hydrogen porosity and oxide inclusions, or defects survive into the forging. |
| Reduction ratio | To close porosity and develop wrought properties, the ingot must be reduced substantially in cross-section. A very thick finished part leaves little room for reduction, which is why the thickest forgings need the largest ingots. |
| Press force and daylight | Aluminium is forged roughly between 400 and 500 °C depending on alloy; it is stiffer than its weight suggests and cools quickly against dies. Press tonnage and the open height between platens cap the section that can be worked. |
| Ring mill capacity | Maximum ring outside diameter, height and weight are set by the ring mill; very tall rings are often forged as hollows instead. |
| Heat-treatment furnace and quench tank | The whole forging must fit into the solution furnace with uniform temperature, and be transferred to the quench quickly enough to avoid strength loss. This often limits large heat-treated parts more than forging does. |
| Inspection access | Ultrasonic testing needs flat or regular surfaces; a large part may be rough-machined to a sonic shape before inspection. |
How a large aluminium forging is made
- Ingot and homogenisingA cast ingot of the specified alloy is homogenised to even out segregation, then scalped and sawn to the calculated weight.
- Pre-heatingThe ingot is soaked to forging temperature; dies and tooling are also pre-heated because aluminium chills quickly on contact.
- Open-die forging or ring rollingUpsetting and drawing in several directions (often called multi-directional forging) refine the structure. Rings are pierced and then rolled to diameter on a ring mill.
- Solution heat treatment and quenchHeat-treatable alloys are solution treated and quenched in water or polymer; quench rate is managed to balance strength and distortion.
- Stress relief and ageingCompression stress relief for Tx52 tempers, then artificial ageing to T6, T73, T74 or similar.
- Machining and inspectionRough machining to a sonic shape, ultrasonic testing, dimensional check, and test coupons cut from prolongations for tensile, hardness and conductivity tests.
Inspection and documentation for heavy forgings
Typical inspection package
- Ultrasonic testing
- To ASTM B594, ASTM E2375 or AMS-STD-2154; acceptance class (for example AA or A) agreed in the order
- Mechanical tests
- Tensile and elongation from coupons in the directions specified; short-transverse tests on thick 7xxx parts
- Electrical conductivity and hardness
- Used to verify temper and over-ageing of 7xxx alloys (T73, T74)
- Macro-etch and grain flow
- Sectioning or etching of a sacrificial piece on first articles to confirm flow lines
- Chemistry
- Heat analysis to the alloy limits of the Aluminum Association / EN 573-3
- Dimensions
- Full check of the forged or rough-machined envelope against the drawing
- Certificate
- EN 10204 3.1 mill certificate; third-party inspection on request
For aerospace and defence work, buyers usually flow down additional requirements such as first-article inspection, approved heat-treat and NDT sources and lot traceability back to the ingot. State these in the enquiry, because they affect both the route and the price.
Large forging vs thick plate, casting and welded fabrication
| Criterion | Open-die forging / ring | Thick rolled plate | Casting | Welded fabrication |
|---|---|---|---|---|
| Internal soundness | Excellent; porosity closed by working | Very good, but centre of very thick plate is less worked | Risk of porosity and shrinkage | Depends on weld quality |
| Directional properties | Grain can follow the part | Fixed by rolling direction; short-transverse weakest | Isotropic but lower | Heat-affected zones are weak spots |
| Fatigue performance | Highest | Good | Lowest | Limited by weld details |
| Material yield | High; near-shape envelope | Low for rings and discs cut from plate | Highest | Good |
| Tooling cost | Low for open-die; high for closed-die | None | Pattern and mould | Fixtures only |
| Best for | Critical, large or fatigue-loaded parts | Prismatic machined parts | Complex low-stress shapes | Large frames with modest loads |
A useful rule: if the finished part is a ring or disc, a rolled ring or upset disc almost always beats cutting it from plate on both properties and material cost. If the part is a rectangular block machined on all faces and is not fatigue critical, thick plate from the ultra-thick plate guide is usually cheaper.
How to specify a large forging and avoid common mistakes
- Send the finished-part drawing, not only a block size. The forging engineer can then design a near-shape envelope and grain direction that suits the loads.
- Name the governing standard and test directions. ASTM B247, EN 586 or a named AMS specification fixes which properties are guaranteed and where coupons are taken.
- Choose the temper for the section. Thick 7xxx parts are normally ordered in T7452 or T7352, not T6, to control stress corrosion and residual stress.
- Agree the ultrasonic class early. Tighter classes may require a more conservative sonic shape and more machining.
- Allow for machining stock. Open-die forgings carry several millimetres of allowance per face; requesting a net-size forging is unrealistic.
- Do not mix up "forged plate" and rolled plate. Forged slabs have different property tables and test directions from rolled plate to ASTM B209.
References and standards
- ASTM B247 – Aluminum and Aluminum-Alloy Die Forgings, Hand Forgings, and Rolled Ring Forgings
- EN 586-1/-2/-3 – Aluminium and aluminium alloys: forgings
- ASTM B594 – Ultrasonic Inspection of Aluminum-Alloy Wrought Products
- AMS-STD-2154 – Inspection, Ultrasonic, Wrought Metals, Process for
- ASM Handbook, Vol. 14A – Metalworking: Bulk Forming (Forging of Aluminum Alloys)
Large aluminium (aluminum) forgings: frequently asked questions
What is the largest aluminium forging that can be made?
It depends on the part shape, alloy and temper rather than a single number. Ingot size, press force, ring-mill capacity and especially the size of the solution furnace and quench tank all set limits. Send a drawing and we confirm whether the part can be forged and heat-treated in one piece.
Why choose a forging instead of cutting the part from thick plate?
A forging has a fully worked, dense structure with grain that follows the part, so it has better fatigue strength and short-transverse properties. For rings and discs it also wastes far less metal than cutting the shape from a plate.
Which alloy is best for very thick high-strength forgings?
7050 in T7452 or T74 is the usual choice because it is much less quench sensitive than 7075, so the centre of a thick section keeps more of its strength, and the over-aged temper gives good stress-corrosion resistance.
What does T652 or T7452 mean on a forging?
The "52" suffix means the forging was stress-relieved by controlled cold compression after quenching. This reduces residual stress so the part stays stable during heavy machining.
How are large forgings inspected?
Typically by ultrasonic testing to ASTM B594 or AMS-STD-2154, tensile tests from coupons in the specified directions, hardness and conductivity checks, chemical analysis and dimensional inspection, documented on an EN 10204 3.1 certificate.
Can you supply large forgings rough-machined?
Yes. Large forgings can be supplied as forged, or rough-machined to a sonic or near-final shape to your drawing, which reduces your machining time and freight weight.
Planning a large forged component?
Send the drawing, alloy, temper, quantity and inspection requirements. Our team will review the forging route and reply with a quotation for worldwide delivery.
