4032 and 4A11 Aluminium Extruded Rod for Pistons
4032 is a 12 % silicon aluminium alloy with copper, magnesium and nickel, designed for forged pistons: it expands less with heat than other wrought alloys and resists wear well. It is supplied as large-diameter extruded rod in F or H112 condition, cut into slugs, forged and then heat-treated to T6. 4A11 is the Chinese equivalent.
- Alloy
- 4032 (≈ 4A11)
- Supply temper
- F / H112
- Diameter
- about 100 – 300 mm
- Final temper
- T6 after forging
Why pistons are forged from 4032
A piston runs hot, cycles millions of times and slides against a cylinder bore. It needs low thermal expansion so clearances stay tight, good strength at elevated temperature, and a wear-resistant surface.
Most production pistons are cast in hypereutectic or eutectic Al-Si alloys. Forged pistons, used in performance, racing, diesel and aircraft engines, are stronger and tougher because forging closes porosity and gives a fine grain flow. 4032 is the forging alloy that comes closest to cast piston alloys in thermal expansion: silicon at 11 – 13.5 % lowers the expansion coefficient to about 19.4 µm/m·°C, versus about 22 – 23 for 2618 and 6061. That lets engine builders run tighter piston-to-bore clearances, with less noise and blow-by when cold.
Copper and magnesium allow precipitation hardening to T6, and nickel forms stable intermetallic particles that help retain strength at operating temperature. The hard silicon particles give wear and scuff resistance in the skirt and ring grooves.
4032 and 4A11 composition (wt %)
| Element | 4032 (AA / ASTM B247) | 4A11 (GB/T 3190) |
|---|---|---|
| Silicon (Si) | 11.0 – 13.5 | 11.5 – 13.5 |
| Copper (Cu) | 0.50 – 1.3 | 0.50 – 1.3 |
| Magnesium (Mg) | 0.8 – 1.3 | 0.8 – 1.3 |
| Nickel (Ni) | 0.50 – 1.3 | 0.50 – 1.3 |
| Iron (Fe) | ≤ 1.0 | ≤ 1.0 |
| Manganese (Mn) | — | ≤ 0.20 |
| Chromium (Cr) | ≤ 0.10 | ≤ 0.10 |
| Zinc (Zn) | ≤ 0.25 | ≤ 0.25 |
| Titanium (Ti) | — | ≤ 0.15 |
| Others each / total | 0.05 / 0.15 | 0.05 / 0.15 |
| Aluminium | Remainder | Remainder |
Nickel is an essential element of both alloys. Composition tables that omit it are incomplete; check that your certificate reports Ni.
Properties of 4032 in T6 condition
The extruded rod is supplied unheat-treated, so these are the properties of the finished, forged and T6-treated part. Typical values from Aluminum Association and ASM data:
| Property | Typical 4032-T6 |
|---|---|
| Tensile strength | about 360 – 380 MPa (52 – 55 ksi) |
| Yield strength (0.2 %) | about 315 MPa (46 ksi) |
| Elongation | about 5 – 9 % |
| Brinell hardness | about 120 HB |
| Fatigue strength (5 × 10⁸ cycles) | about 110 MPa (16 ksi) |
| Modulus of elasticity | about 79 GPa (11,400 ksi) |
| Coefficient of thermal expansion | about 19.4 µm/m·°C (20 – 100 °C) |
| Density | about 2.68 g/cm³ |
| Melting range | about 532 – 571 °C (990 – 1060 °F) |
| Thermal conductivity | about 140 – 155 W/m·K |
The high modulus, about 15 % above most aluminium alloys, comes from the silicon particles and helps piston crowns resist deflection under combustion pressure. Strength falls at sustained temperatures above about 150 – 200 °C, as with all age-hardened aluminium alloys.
Rod sizes and tolerances
Typical supply
- Diameter
- about 100 – 300 mm extruded rod; smaller bar available separately
- Temper
- F (as fabricated) or H112
- Length
- Random or fixed lengths; cut-to-length slugs on request
- Diameter tolerance
- Minus-only, roughly −1.4 to −3.3 mm depending on size and precision grade
- Straightness
- Typically a few mm per metre, tighter on high-precision grade
- Ends
- Saw cut square and deburred
- Inspection
- Macro-etch, microstructure and ultrasonic testing on request
Exact tolerances are confirmed with each order according to the agreed standard and grade.
Forgers usually specify the silicon particle size and distribution, grain structure and freedom from coarse primary silicon, because these control forgeability and machined surface quality. Ultrasonic inspection of the rod helps catch internal defects before they become scrap pistons.
From extruded rod to finished piston
- Cut slugsThe rod is sawn into slugs of the forging weight.
- Preheat and forgeSlugs are heated and forged in closed dies, giving a dense structure and grain flow following the crown and pin bosses.
- Heat treatSolution treatment, quench and artificial ageing to T6 (or a stabilised variant for high-temperature service).
- MachineRing grooves, pin bore, skirt profile and crown are machined. Use sharp carbide or PCD tools: silicon particles are abrasive.
- FinishSkirt coatings, hard anodising of the top ring groove, or thermal barrier crown coatings are applied as needed.
4032 compared with 2618 for forged pistons
| Factor | 4032-T6 | 2618-T61 |
|---|---|---|
| Silicon content | 11 – 13.5 % | about 0.1 – 0.25 % |
| Thermal expansion | About 19.4 µm/m·°C | About 22 – 23 µm/m·°C |
| Cold clearance | Tighter; quieter cold start | Looser; more cold noise |
| Wear resistance | Better | Lower |
| High-temperature strength and toughness | Good | Better; tolerates detonation and boost |
| Typical use | Street performance, mild racing, diesel | Heavy boost, nitrous, endurance racing |
In short: 4032 for engines that spend most of their life on the street and benefit from tighter clearances; 2618 for engines where peak cylinder pressure and temperature dominate.
Applications
- Forged pistons for performance cars, motorcycles and racing engines
- Diesel and compressor pistons
- Aircraft piston-engine components
- Wear-resistant parts such as pulleys, sleeves and compressor scrolls
- Brake and hydraulic components needing low expansion
References and standards
- ASTM B247 – Aluminum and Aluminum-Alloy Die Forgings, Hand Forgings, and Rolled Ring Forgings
- SAE AMS 4145 – Aluminum Alloy Forgings, 4032-T6
- GB/T 3190 – Chemical composition of wrought aluminium and aluminium alloys
- The Aluminum Association – International Alloy Designations and Chemical Composition Limits
- ASM Handbook Vol. 2 – Properties of Wrought Aluminum and Aluminum Alloys: 4032
4032 piston rod: frequently asked questions
Why is 4032 used for pistons?
Its high silicon content gives lower thermal expansion and better wear resistance than other forging alloys, so pistons can run tighter clearances.
What temper is 4032 rod supplied in?
F or H112, unheat-treated. The forger heat-treats the finished forging to T6.
Is 4A11 the same as 4032?
They are essentially equivalent; 4A11 has slightly different silicon and small Mn and Ti limits.
Is 4032 or 2618 better for racing pistons?
2618 for high boost and extreme temperatures because it is tougher when hot; 4032 for street and moderate racing engines where low expansion and quiet running matter.
Is 4032 hard to machine?
It machines cleanly but the silicon is abrasive, so carbide or diamond tooling gives much longer tool life.
Need 4032 forging stock?
Send diameter, lengths, quantity and inspection requirements. We will confirm availability and certification.
