Aluminium Extrusions - Glossary Of Terms

Common Terms in Aluminium

Alloy material that has metallic properties and which is composed of at least two chemical elements, one always being metal. The alloy's properties are usually different from those of the components.   

Anneal to subject to high heat, with subsequent cooling so as to soften and render the product less brittle. 

Annealing any treatment at elevated temperature which has for its principal purpose softening and removal of residual stresses. Often, in wrought aluminium products, "annealing" generally connotes a treatment above the re-crystallisation temperature. 

Aperture the opening or openings in the die tool, of the same cross-sectional area and contour as the product to be extruded. 

Bar a solid section that is long in relation to its cross-sectional dimensions, having a symmetrical cross-section that is square or rectangular with sharp or rounded corners or edges, of is a regular hexagon or octagon, and whose width or greatest distance between parallel faces 3/8" or greater. 

Billet a solid semi-finished round, square or rectangular cast bar produced in different diameters, sizes and lengths for use in the aluminium extrusion process. Billets may be cast to diameter and length (book mould) or cast in logs and cut to length (direct chill). Billets may be solid or hollow (longitudinal hole through centre) and are used in the as-cast or homogenized condition, depending upon end use and alloy. 

Breakaway Point usually formed by the step where the die relief starts and bearing surface ends; also where extrusion leaves bearing. 

Butt the un-extruded portion of the billet remaining in the container after the extrusion cycle is completed. The butt varies in thickness depending upon the billet condition. The butt is sometimes also called heel. 

Cold Working mechanical deformation of metal or alloy at temperatures below those at which re-crystallisation occurs. Cold working aluminium can give increased hardness and improved strength. Cold worked metal may be brought back to the original state of workability by proper annealing. 

Deflection The distortion or bending of the die. Insufficient support of die will cause it to deflect, lessening the effectiveness of the bearing. 

Die The unit of press tooling with one or more machined openings to product the desired extruded section or sections. 

Die Face The surface of extrusion die facing the billet. 

Drawing reducing wall thickness and outside diameter of tubing. It is a cold working process in which an extruded tube bloom is elongated by being pulled through a tapered die or series of tapered dies. A mandrel determines the inside diameter (see sinking). 

Electrical Conductivity is the capacity of a material to conduct or allow the flow of an electric current. Conductivity values for aluminium are expressed as percentages of the conductivity of the International Annealed Copper Standard, which, as indicated below, has a resistive property of 10.371 ohms per mil foot (a wire 0.001" in dia. and 1' long) at 20° C (68 F). 

Electrical Resistive Properties is the electrical resistance of a body of unit length and unit cross-sectional area. The value of 10.371 ohms (mil, foot) at 20° C (68F) is the resistive property equivalent to the International Annealed Copper Standard (IACS) for 100 per cent conductivity, 1 foot in length and 1 circular mil in cross-sectional area, would have a resistance of 10.371 ohms. 

Elongation The linear stretch of material during tensile loading. The increase in distance between two gage marks that results from stressing the specimen in tension or fracture. Original gage length is usually 2" for sheet specimens and round specimens whose diameter is 1/2", or four times the diameter for specimens where that dimension under 1/2". Elongation values depend to some extent upon size and form of the test specimen. 

Etching the application of an etching agent to change the metal surface. 

Extrusion conversion of a billet into lengths of uniform cross-section by forcing metal through or die orifice of the desired cross-sectional outline. 

Extrusion (Direct) the method of extruding wherein the die and ram are at opposite ends of the billet. The product and ram travel in the same direction. 

Extrusion (Indirect) the method of extruding where the die is at the ram end of the billet and the product travels through the hollow ram in the opposite direction.  

Extrusion Pressure that level of force employed to cause cast billet to flow through a die. 

Extrusion Tools the auxiliary equipment required to produce extrusions, which is not an integral or fixed part of the extrusion press. Tools consist principally of container, dummy blocks, replaceable stems, etc. 

Extrusion Speed the rate at which an extrusion exits from the die; this is usually expressed as metres per minute. 

Finishing usually secondary operations applied to extrusions to improve product dimensionally or change surface condition or colour. 

Modulus of Elasticity is the ratio of stress to corresponding strain throughout the range where they are proportional. As there are three kinds of stresses. 

Residual Stresses those stresses set up within a metal as the result of non-uniform plastic deformation which may sometimes be caused by drastic temperature gradients in quenching. 

Shrinkage the contraction of the extrusion due to such factors as cooling; the term is also sometimes used for actual thinning by die deflection. 

Sinking similar to plug drawing except that no inside mandrel or plug is used. Wall thickness is not altered substantially in a sink pass. 

Solution Heat Treatment a process in which an aluminium alloy is heated to a suitable temperature, is held at the temperature long enough to allow certain constituents to enter into solid solution and is then cooled rapidly to hold the constituents in solution. 

Stepped Extrusion an extrusion having one or more abrupt changes in cross section at intervals in its length during production. 

Stepped Extrusion Process a process similar to the conventional extrusion process; however, the extrusion press is stopped when the billet is only partially extruded, and the split dies are removed and replaced with dies of larger opening or orifice.  

Water Stain The superficial etching of the surface from prolonged contact with moisture in restricted air space. Such stains are usually white or gray in appearance. This condition can find its water source from either condensation or wetting.