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Extrusion Terminology


After extrusion the alloys internal crystalline structure changes increasing its mechanical properties. This occurs slowly at room temperature (natural ageing) and more rapidly at elevated temperatures in an oven (artificial ageing).


The base aluminium is improved through the addition of other basic metallic substances. In the case of aluminium extrusions, magnesium and silicon are the most important alloying minerals. Others are copper, zinc, manganese, titanium, bismuth and chromium. The most common alloys used in extrusion are 6063, 6060 and 6082.


An electronic surface-treatment that increases the normally occurring oxide layer on the surface of the aluminium giving greater protection. The thickness of the oxide layer after anodising normally ranges between 5 and 25 microns.. A micron is equal to one thousandth of a millimeter.


A rough edge left after operations such as cutting or drilling.

Circumscribing Circle Diameter (CCD)

The diameter of the circle within which the profile is housed is a measurement of the profile’s size. The term is generally used to indicate the limits of a certain press.


A hollow cylinder in an extrusion press from which the billet is extruded.


The production of a uniform matt finish by controlled chemical (acid or alkali) treatment. Usually occurs as part of the anodising process.


Click here to read our full definition of an Aluminium Extrusion.

Extrusion Die

Normally a round hardened steel plate in which the shape of the profile is cut and through which the semi soft aluminium is pressed to obtain the extruded profile.

Heat-treatable alloy

A type of alloy that obtains its strength through precipitation-hardening (heat-treatment) and which is typically used for extrusions. Alloys that are not heat-treated acquire their strength through increased additives or cold-rolling and are used primarily for sheeting, strip and foil.

Hollow Profile

A profile that includes an enclosed hollow. The simplest version being a round or square tube.

Ingots, Logs and Billets

To produce profiles, the smelter plant casts the aluminium alloy to form round ingots or logs whose diameter is adapted to each press, and in lengths of six to seven meters. These may be cut into shorter lengths (billets) before being loaded onto the extrusion press.

Natural Anodising

Anodising without adding any colour. Since the aluminium oxide is transparent, the natural surface is visible. The surface is usually acid etched before anodising giving it a uniform satin appearance.


The distance along the outer contour (outer perimeter) and inner contour (inner perimeter) of a profile. Generally expressed in millimeters. This measurement is used to calculate the surface area for surface treatment such as anodising or powder coating.

Porthole Die

An extrusion die that contains a mandrel as part of its assembly. Used to produce hollow profiles.

Powder Coating

Aluminium powder coating is the application by electrostatic spray of a thermasetting powder which, when cured, flows to form a visually attractive and hard wearing finish to your aluminium profile. In summary the powder particles melt and fuse to the aluminium creating a hard shell.

Press force

The pressure the extrusion press uses to force the aluminium through the extrusion die. The pressure is normally designated in tonnes per square inch. The majority of extrusion presses use pressures in the range of 1000 to 2200 tones.


An aluminium profile has the same meaning as an aluminium extrusion.


Controlled rapid cooling of a profile from an elevated temperature by use of a liquid or gas to give the profile its mechanical properties.


A process applied after anodising to reduce the porosity of the surface.


An aluminium section has the same meaning as an aluminium extrusion.

Semi-hollow profile

A solid profile with a cavity that is almost closed. May also require a hollow die or the redesigning of the profile.

Solid profile

A profile that does not include any enclosed hollows.

Solid profile

A profile that does not include any enclosed hollows.


Stipulates the levels of mechanical properties (such as hardness) in an alloy achieved by mechanical or thermal treatments. The temper is normally stipulated at the end of the alloy designation. For example 6082T6 where 6082 is the alloy and T6 is the temper .


Superficial surface oxidisation caused by reaction to water or moisture held between closely adjacent metal surfaces. The appearance can manifest itself as white, grey or black blotches.

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