How aluminium profiles are made: the extrusion process explained

Aluminium profiles are made by extrusion: a heated aluminium billet is pushed through a shaped steel die under thousands of tonnes of force, emerging as a continuous profile with the die’s cross section. The profile is then quenched, stretched straight, cut to length and heat treated to a T5 or T6 temper. The alloy is almost always a 6xxx grade such as 6060, 6063 or 6082. This guide walks through each stage, the tempers and tolerances that result, and how the finished profile is treated.

What extrusion is

Extrusion is a forming process that turns a solid cylinder of aluminium into a long profile of constant cross section. The principle is the same as squeezing toothpaste from a tube: soften the metal, then force it through an opening shaped like the part you want. Because the die opening defines the whole cross section, a single die can produce hundreds of metres of identical profile, which is what makes extruded aluminium so economical for railings, frames, fencing and structural sections. The process suits aluminium in particular because its 6xxx alloys stay ductile at extrusion temperature and take fine, complex shapes cleanly.

The aluminium billet

Every profile starts as a billet, a solid round bar of aluminium alloy cast to a set diameter and cut to a workable length. The billet is produced from a controlled alloy composition to EN 573-3, so its behaviour in the press and its final strength are predictable. Before extrusion it is homogenised, a slow heat treatment that evens out the cast structure and dissolves the alloying elements uniformly, which prevents streaking and weak spots in the finished profile. A clean, well homogenised billet is the foundation of a sound extrusion.

Preheating the billet and die

The billet is heated to around 450 to 500 degrees Celsius, hot enough to become soft and plastic but well below melting, so it flows rather than pours. The die, machined from hardened tool steel, is preheated to a matching temperature so it does not chill the metal on contact and cause it to jam or tear. Getting both temperatures right is critical: too cold and the press struggles and the surface roughens, too hot and the profile can blister or drag. This thermal control is where much of the quality of an extrusion is decided.

The extrusion press

The hot billet is loaded into the press container, and a hydraulic ram drives it against the die with thousands of tonnes of force. The aluminium has nowhere to go but through the die opening, so it emerges as a continuous profile in the exact shape of the aperture. The ratio of billet cross section to profile cross section is the extrusion ratio, and it, along with the profile’s complexity, sets how hard the press has to work and how fast the profile can run. Thin, intricate shapes need more force and run slower than simple solid bars.

Solid, hollow and semi-hollow profiles

The die type determines what shapes are possible. A flat die produces solid profiles such as flat bar, angle and channel. A hollow profile, such as tube or box section, needs a porthole or bridge die: the metal splits around a mandrel that forms the internal cavity, then rejoins and welds itself back together under pressure inside the die. These pressure welds are why hollow extrusions are sound and continuous. Semi-hollow shapes, with a partly enclosed void, are the most demanding to tool. For finished hollow sections see our guide to aluminium tube and box section.

Quenching at the press

As the profile leaves the die it is still hot, and how it is cooled starts to fix its temper. The profile is quenched on the runout table, either by forced air using fans and air mist, or by water spray for a faster cooling rate. Air quenching gives good dimensional stability and low distortion and produces a T5 temper. Water quenching cools faster, supports higher strength and leads to a T6 temper, at the cost of a greater risk of distortion that later straightening corrects. The choice depends on the alloy and the strength the profile must reach.

Stretching and cutting to length

Extrusion and quenching leave the profile slightly twisted or bowed, so each length is stretched in tension on a stretcher until it is straight and within tolerance. This stretch also relieves internal stress and improves dimensional stability. The straightened profile, which can run many metres long, is then cut to length on a saw into stock or order lengths. Cutting to length here is a routine part of finishing the extrusion, not a separate machining operation.

Ageing: T5 and T6 tempers

A freshly extruded 6xxx profile is soft, and it reaches full strength through ageing, a controlled low temperature heat treatment that lets fine strengthening particles form in the metal. This is artificial ageing, typically several hours at around 175 degrees Celsius. The temper name records the route.

The practical difference is strength. A 6060 or 6063 profile in T6/T66 reaches roughly 150 to 160 MPa proof strength, and structural 6082 in T6 reaches about 250 MPa. ULAMEX supplies 6060 and 6063 as T6/T66 and treats the two tempers interchangeably, in line with normal stock practice. The full mechanical figures per alloy and temper are in our guide to EN AW aluminium alloys.

Which alloys are extruded

Extrusion is dominated by the 6xxx aluminium-magnesium-silicon family, because these alloys combine good extrudability, corrosion resistance and heat treatable strength.

6060 and 6063 give the cleanest surface and take anodising and coating well, which is why they dominate visible architectural work. 6082 trades a little surface quality for markedly higher strength, so it goes into load bearing sections. Alloy choice is a balance of strength, finish and the complexity of the shape being pushed.

Tolerances and standards

Extruded profiles are made to European standards that define both their strength and their dimensions. EN 755-2 sets the mechanical properties for each alloy and temper, EN 755-9 sets the dimensional tolerances for standard profiles, and EN 12020-2 sets the tighter tolerances for precision profiles in 6060 and 6063. Composition follows EN 573-3. Because these standards are public and verifiable, a profile ordered to a named alloy, temper and standard has a defined and repeatable specification, which is what a fabricator needs to design with confidence.

Finishing the profile

A profile leaves the press with a mill finish, the natural surface of the extruded metal, which is perfectly serviceable indoors and for hidden structure. For appearance or extra durability it is finished. Powder coating applies a thick coloured layer in the full RAL range and is the standard architectural finish. Aluminium also anodises well, building up its own oxide layer into a hard integral finish, with 6063 giving an especially bright anodised result. Our guide to anodising versus powder coating compares the two routes and when each is the better choice.

Why extrusion suits aluminium

Extrusion plays to aluminium’s strengths. The metal is light, about a third of the weight of steel, so complex profiles stay easy to handle. It flows cleanly through fine die detail, so a single extrusion can integrate screw channels, snap fits and stiffening ribs that would otherwise need assembly. And the same profile can be produced in long, uniform runs at low cost per metre. That combination of light weight, shape freedom and repeatability is why extruded aluminium is the default for framing, fencing, solar mounting and countless engineered sections.

Extruded aluminium profiles from ULAMEX

ULAMEX has supplied extruded aluminium since 1988, in the grades and finishes that suit the job.

Need a standard or custom extruded profile? Send ULAMEX the alloy, temper and cross section, or a drawing, and the desk will return a non-binding quotation. See our guides to aluminium profiles and aluminium tube, and our supply capabilities, or contact the export desk at [email protected] or +48 504 424 761.

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