Stepped shaft
Several diameters forged in one piece for bearing seats, seal faces and gear hubs. Open-die forging with stepped tooling produces the profile; final diameters are turned.
Shaft forgings
Aluminium Forged Shafts: Solid, Stepped, Hollow and Flanged
An aluminium forged shaft is a shaft blank shaped by open-die or closed-die forging so that the grain follows its steps, shoulders and flanges, giving better fatigue life than a shaft turned from bar. Metline supplies forged shafts in 6061, 6082, 2014, 7075 and 7050, rough forged, proof machined or finished to drawing, with ultrasonic testing and EN 10204 3.1 certificates, to customers worldwide.
- Shapes
- Solid, stepped, hollow, flanged
- Alloys
- 6061 · 6082 · 2014 · 7075 · 7050
- Tempers
- T6, T652, T73, T7352, T74
- Supply
- Forged, proof or finish machined
Why forge an aluminium shaft?
Most small aluminium shafts are simply turned from extruded or rolled round bar. Forging becomes worthwhile when a shaft has large changes in diameter, an integral flange, or a duty where fatigue governs the design. Forging the steps and flanges close to final shape keeps the grain flowing around each shoulder instead of cutting through it, and saves the metal that would otherwise be machined away from a bar as large as the biggest diameter.
In a shaft machined from bar, the grain runs straight along the axis. At every shoulder, where the diameter changes and stress concentrates, the machined surface cuts across the grain ends, and that is exactly where fatigue cracks start. In a forged shaft the grain bends with the contour of the shoulder or flange, so the most heavily stressed surface is parallel to the grain. Forging also consolidates any residual porosity in the cast billet, which improves the ultrasonic quality of large diameters.
Aluminium shafts are chosen for low rotating mass and inertia, corrosion resistance and non-magnetic behaviour: propeller and drive shafts for motorsport and drones, rotor shafts for lightweight motors, actuator and linkage shafts in aircraft, rollers and spindles in packaging and printing machines, and shafts for marine and food equipment that must not rust.
Types of aluminium forged shafts
Flanged shaft
An integral flange upset at one or both ends for a bolted coupling, removing a welded or shrink-fitted flange and its failure point.
Hollow shaft
Forged over a mandrel or bored after forging to cut weight and inertia. For a given outside diameter a tube loses little torsional stiffness while losing much of its mass.
Rotor and spindle shaft
Balanced, precision-machined shafts for small motors, drones, fans and spindles, usually in 7075 or 2014 for strength at small diameters.
Eccentric and cranked shaft
Offset journals forged close to shape in closed dies, used in light pumps, compressors and mechanisms.
Shaft blank / forged bar
A simple forged round with a machining allowance, for customers who do all the turning in-house. See forged bar.
Which aluminium alloy for a forged shaft?
Shafts are usually sized by torsional and bending fatigue, so fatigue strength matters as much as tensile strength. Aluminium has no true endurance limit, so published fatigue strengths are quoted at a fixed number of cycles (5 × 108 for the R. R. Moore rotating-beam test). The table compares typical values.
| Alloy / temper | Typical tensile | Typical yield | Fatigue strength (5×10⁸) | Shear strength | Comment |
|---|---|---|---|---|---|
| 6061-T6 | 310 MPa | 275 MPa | 97 MPa | 207 MPa | Economical, corrosion resistant, weldable |
| 6082-T6 | 310 MPa | 260 MPa | ≈ 95 MPa | ≈ 210 MPa | European equivalent of 6061, good in thick sections |
| 2014-T6 | 485 MPa | 415 MPa | 124 MPa | 290 MPa | Classic forging alloy; protect against corrosion |
| 7075-T6 | 570 MPa | 505 MPa | 159 MPa | 330 MPa | Highest strength; susceptible to stress corrosion |
| 7075-T73 | 505 MPa | 435 MPa | ≈ 150 MPa | ≈ 300 MPa | Preferred where stress-corrosion cracking is a risk |
| 2618-T61 | 440 MPa | 370 MPa | 125 MPa | 260 MPa | Keeps strength at 150 – 250 °C |
Typical values from Aluminum Association and ASM data, for comparison only. Values marked ≈ are approximate. Design to the specified minimums of ASTM B247, EN 586-2 or your AMS specification, with appropriate fatigue knock-down factors for keyways, splines and surface finish.
Design considerations for aluminium shafts
Stiffness
Aluminium has about one-third the elastic modulus of steel (69 GPa against 200 GPa; shear modulus about 26 GPa). An aluminium shaft of the same diameter twists and deflects three times as much, so aluminium shafts are usually larger in diameter, often hollow, to recover stiffness and critical speed.
Critical speed
Whirling speed depends on stiffness divided by mass. Because aluminium is a third as stiff but also a third as dense as steel, a larger-diameter aluminium tube can reach the same or a higher critical speed than a steel shaft, which is why long propeller shafts are often aluminium.
Bearing journals
Aluminium is soft compared with bearing steel. Use bearings with a steel inner race, press on a steel sleeve, or hard anodise the journal (Type III, typically 25 – 50 µm) for wear and fretting resistance.
Thermal expansion
Aluminium expands about twice as much as steel (23 against 12 µm/m·°C). Interference fits with steel bearings loosen as the assembly warms, so fits must be checked at the operating temperature.
Stress raisers
Generous fillet radii at shoulders, rolled rather than cut threads where possible, and smooth keyway ends matter more in aluminium than in steel because fatigue strength is notch sensitive.
Galvanic contact
Where an aluminium shaft meets steel gears or couplings in a wet environment, isolate the metals or seal the joint to avoid galvanic corrosion of the aluminium.
Supply conditions, sizes and tolerances
Typical supply scope
- Forging route
- Open-die (stepped, flanged, long shafts) or closed-die (repeat production of complex ends)
- Diameter
- From about 30 mm to several hundred millimetres; maximum depends on alloy and length
- Length
- Short stub shafts to long forged bars; long shafts may be forged in stages
- Supply condition
- Rough forged, proof machined for UT, or finish machined with keyways, splines and threads
- Machining
- CNC turning, deep-hole boring, keyways, splines, threads, dynamic balancing on request
- Typical finish tolerance
- To drawing; precision bearing seats commonly held to ISO h6/k6 grades with run-out controlled
Limits are confirmed against each drawing. A forged shaft is always quoted with a machining allowance unless supplied finished.
Forged shafts are quoted with a machining allowance on every diameter and face, enough to remove the forging skin, oxide and any surface laps and to correct the distortion that follows quenching. For shafts with tight run-out requirements, specify a stress-relieved temper such as T652 or T7352 and rough machining before final turning; this keeps residual stress from bending the shaft as material is removed.
Inspection and documentation
| Inspection | Standard / method | Purpose |
|---|---|---|
| Ultrasonic testing | ASTM B594 or AMS-STD-2154 (class to order) | Finds internal flaws before costly machining |
| Tensile and hardness tests | ASTM B557 / EN ISO 6892-1; Brinell or Rockwell | Confirms properties of the heat-treat lot |
| Conductivity (7xxx) | Eddy current, % IACS | Confirms correct over-aged temper (T73, T74) |
| Dimensional report | Micrometers, CMM, run-out on centres | Checks diameters, lengths, run-out and concentricity |
| Penetrant inspection | ASTM E1417 on finished surfaces, on request | Detects surface laps or cracks at fillets and keyways |
| Certificates | EN 10204 3.1; heat-treatment records; certificate of conformity | Traceability from billet to finished shaft |
Tell us the inspection class and any customer or third-party witness requirements at the enquiry stage, because they affect the forging size (a sonic shape needs extra allowance) and the schedule.
Applications by industry
| Industry | Typical shaft | Usual alloy and temper |
|---|---|---|
| Aerospace | Flight-control and actuator shafts, torque tubes, linkages | 7075-T73, 7050-T74, 2014-T6 |
| Motorsport and automotive | Propeller shafts, axle and steering parts, yokes | 6061-T6, 7075-T6, 6082-T6 |
| Drones and electric motors | Rotor and spindle shafts, balanced | 7075-T6, 2014-T6 |
| Packaging and printing | Rollers, idlers and light spindles | 6061-T6, 6082-T6 |
| Marine and food equipment | Light shafts that must not rust | 6061-T6, 5083 (low strength) |
| Hot environments | Compressor and fan shafts near engines | 2618-T61 |
Heavily loaded industrial shafts in turbines, rolling mills, gearboxes and engines are normally made from alloy steel because of its higher stiffness and fatigue strength. Aluminium is the right choice where mass, inertia, corrosion resistance or non-magnetic behaviour outweigh those advantages.
How to order forged shafts
- SpecifyAlloy and temper, drawing with all diameters, lengths, fillets and tolerances, quantity and supply condition.
- Quality planGoverning standard (ASTM B247, EN 586 or AMS), UT class, test directions, and certificate type (EN 10204 3.1 or 3.2).
- QuoteWe confirm forging route, machining allowance, inspection and delivery terms (EXW, FOB, CIF or DAP).
- ManufactureForging, heat treatment, testing, then rough or finish machining as ordered.
- Pack and shipShafts are protected, end-capped where bored, and crated for sea or air freight with full documents.
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 (delivery conditions, properties, tolerances)
- ASTM B594 – Ultrasonic Inspection of Aluminum-Alloy Wrought Products
- SAE AMS-STD-2154 – Inspection, Ultrasonic, Wrought Metals
- SAE AMS 2770 – Heat Treatment of Wrought Aluminum Alloy Parts
Aluminium forged shafts: frequently asked questions
Is a forged aluminium shaft stronger than one machined from bar?
Its static strength is similar for the same alloy and temper, but its fatigue performance at shoulders and flanges is better because the grain follows the contour instead of being cut through. Forging also reduces material waste when the shaft has large steps or flanges.
Which aluminium alloy is best for a drive shaft?
6061-T6 is the economical, corrosion-resistant choice. 7075-T6 gives the highest strength and allows thinner walls; 7075-T73 is preferred where stress-corrosion cracking is a concern. 2014-T6 is a long-established forging alloy with high strength.
Can aluminium shafts run in bearings directly?
Aluminium is too soft for most plain-bearing journals. Rolling-element bearings with a steel inner race work well; for wear surfaces, use a steel sleeve or hard anodise the journal.
Can you supply hollow forged shafts?
Yes. Hollow shafts are forged over a mandrel or deep-hole bored after forging. A hollow section keeps most of the torsional stiffness of a solid shaft with much lower weight and inertia.
Do you supply finished shafts or only forgings?
Both. Shafts can be supplied rough forged, proof machined for ultrasonic inspection, or finish machined with keyways, splines, threads and balancing to your drawing.
Why is aluminium not used for heavy industrial shafts?
Steel is about three times stiffer and has higher fatigue strength, so heavily loaded turbine, mill and gearbox shafts are steel. Aluminium is chosen where low mass, low inertia or corrosion resistance is the priority.
Need a forged aluminium shaft?
Send your drawing, alloy, quantity and inspection requirements. Our team will propose the forging route and quote a delivered price.
