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Aluminum Processing Glossary

Please click on the letter range below that contains the first letter of the term you would like to learn more about. A - D | E - K | L - Z Aluminum Anodizers Council (AAC) A national body representing anodizers responsible for establishing anodizing specifications. Aluminum Association (AA) A national body representing aluminum producers responsible for establishing aluminum specifications. Aluminum Extruders Council (AEC) A national body representing aluminum extruders. Abrasions Light marks or scuffs on the metal surface generally caused by handling or packing materials. Age Hardening An ageing process that results in increased strength and hardness. Age Softening Spontaneous decrease of strength and hardness that takes place at room temperature in certain strain hardened alloys containing magnesium. Ageing Precipitation from solid solution resulting in a change in properties of an alloy, usually occurring slowly at room temperature (natural ageing) and more rapidly at elevated temperatures (artificial ageing). Alloy A substance with metallic properties, composed of two or more chemical elements of which at least one is a metal. More specifically, aluminum plus one or more other elements, produced to have certain specific, desirable characteristics. Alumina Aluminum oxide produced from bauxite by a complicated chemical process. It is a white powdery material that looks like granulated sugar. Alumina is an intermediate step in the production of aluminum from bauxite, and is also a valuable chemical on its own. Aluminum A silver-white soft metal, noted for its lightness, high reflectivity, high thermal conductivity, nontoxicity, and corrosion resistance. It is the most abundant metallic element, comprising about 1/12th of the earth's crust. It is never found in nature as an elemental metal, but only in combination with oxygen and other elements. In ordinary commercial and industrial use, the word aluminum is often understood to mean aluminum alloy, rather than the pure metal. Aluminum Oxide A chemical compound of aluminum with oxygen, which forms immediately on an unprotected aluminum surface exposed to air. Unlike iron oxide (the rust which forms on steel) aluminum oxide does not flake off, but forms a protective layer that blocks further oxidation and so protects the integrity of the metal. It is transparent and does not alter the appearance of the aluminum surface. Anodic Film The aluminum oxide layer created after anodizing Anodizing Forming a coating on a metal surface produced by electrochemical treatment through anodic oxidation. This process may be used to increase the protective effect of aluminum's transparent natural oxide surface. It may also be given a decorative coloration. Return to top Bauxite One of the ores from which alumina is extracted and from which aluminum is eventually smelted. Bauxite usually contains at least 45 percent aluminum oxide (alumina), and the best grades have a low silica content. About four pounds of bauxite is required to produce one pound of aluminum. Billet, Extrusion May be solid or hollow in form, commonly cylindrical, used as the final length of material charged into the extrusion press cylinder. It is usually a cast product, but may be a wrought product or sintered from powder compact. Blister A raised area on the surface of an extruded product due to subsurface gas expansion during extrusion or thermal treatment. Blistering A defect in the paint film appearing as bubbles, usually caused by the expansion of air, solvent vapor, or moisture trapped beneath the film. Bow Longitudinal curvature of rod, bar, profiles (shapes), and tube. Bow is measured after allowing the weight of the extrusion to minimize the deviation. Bow can be caused by a non-uniform extrusion rate across the cross section resulting in one portion of the extrusion being longer than the other or non-uniform contraction during quenching. Bright Dipping Chemical polishing of aluminum, often by treatment with a mixture of nitric acid and phosphoric acid, yielding a mirror-shiny (specular), highly reflective surface. It is almost always followed by anodizing to protect the surface and provide some choice of colours. Buffing A mechanical finishing operation in which fine abrasives are applied to a metal surface by rotating fabric wheels for the purpose of developing a lustrous finish. Burr A thin ridge of roughness left by a cutting operation such as slitting, trimming, shearing, blanking, or sawing. Return to top Caustic (Sodium Hydroxide, NaOH and derivatives). The active ingredient in an alkaline bath, generally with a pH higher than 10, which removes aluminum from used extrusion dies by etching. The primary ingredient, Caustic Soda (NaOH), dissolves the aluminum alloy by chemical reactions with no affect on the die steel. Chatter A surface defect consisting of alternating ridges and valleys at right angles to the direction of extrusion. Chatter Mark Numerous intermittent lines or grooves that are usually full width and perpendicular to the extrusion direction. Chemical Polishing Improving the surface luster of metal by chemical treatment. Circumscribing Circle The smallest circle that will completely enclose the cross section of an extruded shape. Coefficient of Thermal Expansion The relative rate at which a substance expands on heating, compared to a standard rate. Concentricity Conformance to a common center as, for example, the inner and outer walls of round tube. Conductivity The ability of a substance to transmit heat, light or electricity. Aluminum has high electrical and thermal conductivity, making it useful in a wide range of electrical and heat-exchanging applications. Conversion Coating A chemical layer formed on the metal in the pre-treatment process which aids in paint adhesion and corrosion resistance. Corrosion The deterioration of metal by chemical or electrochemical reactions with substances in its environment. Corrosion (Galvanic) Corrosion associated with the current of galvanic cell consisting of two dissimilar conductors in an electrolyte or two similar conductors in dissimilar electrolytes. Aluminum will corrode if it is anodic to the dissimilar metal. Corrosion (Intergranular) Corrosion occurring preferentially at grain boundaries (also termed intercrystalline corrosion). Corrosion (Pitting) Localized corrosion resulting in small pits or craters in a metal surface. Corrosion (Stress Cracking) Failure by cracking resulting from selective directional attack caused by the simultaneous interaction of sustained tensile stress at an exposed surface with the chemical or electro-chemical effects of the surface environment. The term is often abbreviated SCC which correctly stands for stress corrosion cracking. Corrosion (Water Stain) Superficial oxidation of the surface with a water film, in the absence of circulating air, held between closely adjacent metal surfaces Cryogenic Pertaining to very low temperatures. Aluminum gains strength as temperature is reduced, making it an appropriate material for cryogenic applications. Return to top Deburring Removing burrs, sharp edges, or fins from metal parts by filing, grinding, or tumbling. Die In extrusion a tool with an opening through which heated aluminum is forced by pressure, taking on that cross-sectional shape. Die Assembly In an extrusion press, the die and its associated tooling. Die Face The surface of an extrusion die facing the billet. Die Holder The press component which is located between the container and press platen to retain the extrusion die and its components. It may take many different forms and added functions depending upon its design. The holder can be unlocked and the die withdrawn for the removal of butt and scrap. Die (Hollow) A steel extrusion tool which forms extruded closed profiles containing one or more voids such as rectangular tubing. The tool generally consists of a die cap which generates the outer surface of the profile and the mandrel or core which generates the inside contour. Hollow or semi-hollow profiles are produced usually with either bridge, porthole or spider (taper seal) type dies or variants thereof. Extruded sections produced on such dies have seams or longitudinal weld lines, due to the metal flow around the web supports (bridges) that hold the mandrel. The latter determines the inside contour of the profile being extruded. After flowing around the supports, the metal is fused in a weld chamber before passing through the die (die cap) proper Die Lines A longitudinal depression or protrusion formed on the surface of drawn or extruded material. Die lines are present to some degree in all extrusions and are caused by a roughening of the die bearing. Die Number The number assigned to a die for identification and cataloguing purposes, and which usually is assigned for the same purpose to the product produced from that die. Die Ring A cylindrical sleeve that holds the die and backer in axial relationship to each other. Die (Semihollow) A circular steel extrusion tool which forms an open profile with a high tongue ratio. Generally this tongue ratio is greater than three to one. This type of die is similar to a hollow die. The tongue is protected by a web or bridge which reduces the billet pressure. When possible, for maximum support the tongue should be bolted to the web. Die Slide The extrusion press component located between the container and press platen. It supports, aligns to the press and retains the tooling (die, backer, bolster, sub-bolster, etc.) for the specified profile, as a unit. It may be designed to facilitate butt shearing and to provide die accessibility for replacement and repairing. Die (Solid) A steel disk, with one or more orifices or apertures, of similar cross-section and contour as the desired product, through which metal is forced forming open profiles such as bar, channel and angle. Die Stop A defect resembling a weld around the entire extruded section, caused by stopping a press during extrusion and then restarting it. Die Tool Assembly The various components making up the assembly within the tool carrier or Die Slide. A typical example would be (from front to rear): die and backer enclosed in a die ring, bolster and possibly a sub-bolster or spacer. Die Weld A region in extruded hollow profiles created by two streams of metal within the die joining themselves in the weld chamber around the mandrel of a hollow type die. Die welds are generally present in all extruded hollow profiles and in most cases are not visible. Dove-tail An interlocking connection frequently used for the assembly of interconnecting extrusions; it is assembled by a sliding action. Ductility The property that permits permanent deformation before fracture by stress in tension. More Glossary or Return to top