What Is Aluminum Extrusion?
Aluminum extrusion pushes heated aluminum alloy through a steel die to create profiles with a constant cross-section. The concept is identical to plastic extrusion — except you’re working with metal at 900°F instead of polymer at 400°F, and the resulting parts are structural, conductive, and precisely dimensioned.
What surprises most people: custom aluminum extrusion tooling is cheap. A custom die can cost as little as $500–$2,000 for simple profiles. That’s less than most injection mold engineering charges. If you need a custom cross-section in aluminum, extrusion is almost certainly the most economical path.
How the Process Works
- Billet heating. A cylindrical aluminum billet (6–12″ diameter, several feet long) is heated to 800–950°F — hot enough to be soft and ductile but still solid.
- Pressing. A hydraulic ram pushes the billet through a steel die at 2,000–15,000+ PSI. The aluminum flows through the die opening and emerges as a continuous profile.
- Cooling. The profile is quenched — either with water spray, air, or fans at the press exit. Quench rate affects final metallurgical properties (temper).
- Stretching. The profile is pulled through a stretcher to straighten it and relieve internal stresses (typically 0.5–2% elongation).
- Cutting and aging. Profiles are cut to length, then artificially aged in an oven (typically 350°F for several hours) to reach full temper hardness (T5 or T6).
Why Aluminum?
- Strength-to-weight ratio. Aluminum is roughly one-third the density of steel with useful structural strength. Extruded 6061-T6 has a yield strength of 35,000 PSI.
- Corrosion resistance. Forms a natural oxide layer. Add anodizing and it’s effectively maintenance-free outdoors.
- Thermal and electrical conductivity. Heat sinks are one of the most common extrusion applications for exactly this reason.
- Recyclability. Aluminum recycles with about 5% of the energy needed to produce virgin metal. Scrap from extrusion is nearly 100% recovered.
- Machinability. Extruded profiles can be easily drilled, tapped, milled, and cut with standard tooling.
Common Alloys
- 6063 — The most common extrusion alloy. Excellent surface finish, good corrosion resistance, moderate strength. Architectural trim, frames, railings, lighting fixtures.
- 6061 — Stronger than 6063, good machinability, weldable. Structural components, machine frames, brackets, automotive.
- 6005A — Bridge between 6063 and 6061. Good extrudability with higher strength than 6063. Rail vehicles, truck bodies.
- 7075 — Very high strength (comparable to many steels). Difficult to extrude, expensive. Aerospace, high-performance applications. Not commonly extruded in complex shapes.
What It Costs
This is where aluminum extrusion really shines:
| Cost Element | Typical Range |
|---|---|
| Simple solid die | $500 – $1,500 |
| Hollow die (porthole) | $1,500 – $5,000 |
| Complex multi-void die | $3,000 – $10,000 |
| Die life | 10,000 – 100,000+ lbs of aluminum |
| Aluminum cost (per lb, extruded) | $2.50 – $6.00 |
| Minimum order | 200 – 500 lbs (typical) |
Compare that die cost to a custom injection mold ($15K+), CNC machining a profile from bar stock (slow, wasteful), or steel fabrication (labor-intensive). For any application that can use a constant cross-section, extrusion is remarkably cost-effective.
What You Can (and Can’t) Extrude
Design Freedom
- Hollow sections — Tubes, multi-cell profiles, complex internal chambers. Hollow dies (porthole type) can produce remarkably intricate internal geometry.
- Integrated features — Screw channels, snap-fit tracks, heat sink fins, T-slots, hinge features — all in one piece, no assembly required.
- Thin walls — Down to 1 mm for 6063, ~1.5 mm for 6061. Fin thickness on heat sinks can be even thinner.
- Asymmetric profiles — No requirement for symmetry, though balanced designs extrude more easily.
Design Constraints
- Constant cross-section only. The profile is the same from end to end. Any 3D features require secondary machining.
- Circumscribing circle. The profile must fit within the billet diameter. Most press capacities handle a 6–10″ circumscribing circle. Larger is possible but limits extruder choice.
- Wall thickness uniformity. Large variations in wall thickness cause differential metal flow and can distort the profile. Keep the ratio of thickest to thinnest wall under 3:1 when possible.
- Tongue ratio. Deep, narrow slots (where the tongue of die steel is long relative to its base) are difficult. The die steel can deflect or break. Typical limit: tongue depth/width ratio under 3:1.
- Sharp corners. Internal corners need minimum 0.5 mm radius (1 mm preferred). External corners can be sharper.
Common Applications
- Heat sinks — Extruded finned profiles are the standard for LED lighting, power electronics, and amplifiers.
- Structural framing — T-slot framing systems (80/20-style), machine frames, conveyor structures, workstation frames.
- Enclosures — Electronics housings, channel enclosures with slide-in covers, instrument cases.
- Architectural — Window and door frames, curtain wall mullions, railings, trim.
- Transportation — Truck body framing, trailer cross-members, rail car structure, bicycle frames.
- Solar — Mounting rails, panel frames, racking system components.
- Consumer products — Furniture legs, handles, appliance trim, display fixtures.
Finishing Options
- Mill finish — As-extruded. Fine for internal/structural use.
- Anodizing — Type II (decorative, 0.3–1.0 mil) or Type III hard anodize (1–3 mil, wear-resistant). Clear, black, bronze, gold, and custom colors available.
- Powder coating — Any color, excellent durability. Standard for architectural applications.
- Painting — PVDF/Kynar for long-term exterior exposure (20+ year color retention).
- Brushed/polished — Mechanical finishing for decorative applications.
- Chromate conversion — Thin chemical coating for corrosion protection and paint adhesion.
Extrusion vs. Other Processes
| Need | Best Process |
|---|---|
| Custom aluminum cross-section | Extrusion (lowest tooling, fastest) |
| Complex 3D aluminum part | CNC machining or die casting |
| Sheet metal enclosure | Stamping/bending (but extrusion may integrate features and eliminate assembly) |
| Steel structural member | Roll forming or structural steel (but aluminum extrusion saves weight) |
| Small/intricate aluminum part | Die casting or machining |
The Hidden Advantage: Consolidation
The real power of aluminum extrusion isn’t just making a profile — it’s eliminating assembly. A custom extrusion can integrate mounting channels, wire raceways, structural ribs, snap-fit features, and decorative surfaces into a single piece. What might be 5 separate stamped and fastened components becomes one extrusion cut to length. Fewer parts, less labor, better consistency.
This is where engineers leave the most value on the table: they design with standard shapes and assemble, when a $1,500 custom die could eliminate half the BOM.
Bottom Line
Aluminum extrusion is one of manufacturing’s best-kept open secrets. Custom tooling is cheap, lead times are reasonable (4–6 weeks for a new die), and the design freedom is substantial. If you need a custom metal profile — structural, thermal, architectural, or functional — aluminum extrusion should be your first call. The only hard constraint: constant cross-section. Everything else is surprisingly flexible.