Aluminium Glossary


Ageing, Age Hardening, Precipitation Hardening

The second stage in the process (solution treatment and ageing) for those aluminium alloys that respond to heat treatment as a means of increasing their mechanical properties. It entails the precipitation of a constituent from a supersaturated solid solution. The rate of precipitation, and hence ageing, is both temperature and time dependent, with some alloys ageing at room temperature. It is more usual to perform ageing at higher temperatures. It should be noted that routinely operating aged alloys at unusually high ambient temperatures will permit further ageing and even over ageing leading to loss of properties.

Related Terms: Aluminium Alloy Classifications
All-Over Marking

A method of identifying sheet, plate and strip by printing at close intervals over the surface the name or symbol of the manufacturer, the relevant specification number and, in some cases, the temper and thickness of the material.

A combination of two or more metals, or of metals and other elements. An alloy is formed by adding the 'alloying elements' to the 'parent' metal in the molten state. The parent metal usually accounts for more than 50% of the resultant mixture. Stainless Steel is an alloy of Iron plus Chromium (minimum 10.5%) with a small amount of Carbon plus various other elements (such as Nickely, Molybdenum, Titanium, Manganese) depending upon the grade.
Alloying Element

An element intentionally introduced in controlled quantity into a base metal or an alloy.

Alocroming, Chromating, Alocrom
A family of proprietary chemical conversion coating processes based on chromate (hexavalent chromium) solutions that act as a surface pre-treatment before painting or insulation foaming. This also increases the corrosion resistance. More environmentally benign processes based on trivalent chromium are being introduced.

Aluminium Oxide – A white powder that is produced from the aluminium ore Bauxite and then smelted to produce aluminium metals.

Related Terms: Hall Heroult Process
Aluminium Alloy

A metallic substance, consisting of an intentional admixture of elements, the predominant element being aluminium.

Aluminium Alloy Classifications

Wrought aluminium alloys are specified in British, European and other National standards and are classified in an agreed 4 digit system.

They fall into 2 distinct sub groups:-

1xxx, 3xxx and 5xxx series that develop strength by cold working, the number will be followed by the digit H and other numbers referring to the degree of annealing or cold work, e.g. 3105H22.

2xxx, 6xxx, 7xxx and 8xxx alloys that develop properties by solution treatment and precipitation hardening. The number is usually followed by a T and a number, defining the heat treatment condition of the alloy, e.g. 6082T6.

Thus the 4 digits, the letter and following digits for a product clearly define the chemical composition and the mechanical properties of that material.

Related Terms: Temper Designations

The relative orientation of two adjacent faces of a section generally measured over the full length of both.


Thermal treatment intended to soften a metal or alloy hardened by cold work or artificial ageing.

An electrochemical method for artificially thickening the naturally occurring oxide surface film on Aluminium and Aluminium Alloy surfaces ti improve appearance and/or corrosion resistance. Not all alloy grades are suitable for decorative anodising, with the general rule being the purer the aluminium, the better it will anodise. The thickness and other film characteristics can be controlled to meet varied requirements for improved corrosion resistance, improved abrasion resistance, electrical insulation or as a pre-treatment for subsequently applied coatings. Colour can also be applied using dyes. Anodising film thickness is typically 5 to 25 microns.
Related Terms: Anodising Quality Material
Anodising Quality Material
Material with characteristics that make it suitable for decorative anodising after a suitable preliminary treatment
Anodising Test

A non-destructive test for detecting certain defects in material that is anodized and rinsed. If cracks or other superficial flaws are present in the material they retain some of the chromic acid solution which subsequently seeps out and stains the anodic film

Architectural Anodising

Anodizing to be used in permanent, interior, exterior and static situations where both attractive appearance and long life are essential.

Arrested Mandrel

A mandrel attached to an auxiliary extrusion ram. As the main ram moves forward the mandrel is held stationary in the die, resulting in a product of uniform wall thickness along the length.

Artificial Ageing, Precipitation Treatment
The thermal treatment of an alloy that increases the hardness and strength by precipitation of constituents from the super-saturated solid solution at above room temperature.
As-Quenched Condition
The condition of an alloy during the time immediately following the quench and before the mechanical properties have been significantly raised by precipitation hardening (ageing).


Back Extrusion

A process in which a heated ingot in an enclosed container is extruded backwards over the mandrel and supporting stem.

Back-End Defect
A defect found in extruded products due to incorrect extrusion procedures at the mill.

A round, rectangular or regular polygonal solid section supplied in straight lengths. The term is applied to materials of not less than 6mm diameter or minor dimension.


The treatment of articles in a rotating tumbling container in the presence of abrasives and water for deburring or to produce a variety of surface textures.


Consignment, or a part thereof, comprising products of the same grade or alloy, temper and thickness or cross section, processed in the same manner.

The main ore of aluminium, found in great abundance in the earth’s crust, near the surface. It is mined using open cast mining and has a yield of 25%.
Bayer Process
A chemical process used to refine the aluminium ore bauxite into alumina (aluminium oxide) from which the aluminium metal can be extracted by smelting
Bend Radius
The radius of curvature of the former around which a specimen is bent.
Bend Test
The bending of a specimen to conform with a predetermined radius and angle, to assess bending characteristics and ductility.
Billet, Bloom
Cast aluminium in the form of large round (or occasionally square) bars.
Bite Mark

A mark on the roll coating caused by the initial feeding of the ingot, which is subsequently transferred to the hot rolled slab.

A work-piece prepared for subsequent processing e.g. by forming, bending, cupping, drawing, impact extrusion, pressing, etc.

The production of circles and other shapes by shearing on a blanking press.

Blanking Die

A die used for shearing circles and other blanks.

Blanking Press

A press used for shearing blanks from plate, sheet or strip.

Blast Cleaning

The projection of abrasive grit, sand, small grit blasting particles of steel, glass or other materials, sand blasting or a mixture of abrasive grit, water and air, shot blasting to strike the surface of an article in order vapour blasting to clean it. A matt or satin finish is produced, depending upon the particle size used.


A raised area on the surface of the metal caused by the expansion of a gas enclosed in a sub-surface void.

Bond Blister

A blister at the interface between the coating and the core of clad products.

Bore Test

A test on tube to verify freedom from constriction by passing a metallic bob or wire of specified dimensions through the tube.

Bored Extrusion Ingot

An extrusion ingot with a central bored extrusion billet longitudinal hole produced by machining.

The deviation of the edges from the true longitudinal axis of a product seen as an arc.
Brazing Rod

Rod of an alloy with a low melting range for use as filler metal in brazing.

Brazing Sheet, Strip & Wire

Sheet of a low melting range alloy or clad with a low melting range alloy, used for brazing.

Strip of a low melting range alloy or clad with a low melting range alloy, used for brazing.

Wire of an alloy with a low melting range for use as filler metal in brazing.

Bright Anodising

Anodizing with brightness as a primary objective.

Buckle, Ripple
The variation in flatness represented by alternate bulges and hollows along the length of a rolled product, the edges of which remain reasonably flat.
Bull Block

A machine for drawing rod, bar and tube in coil form through one die.


A thin ridge of roughness on an edge left by a cutting operation such as slitting, trimming, shearing, blanking, sawing etc.

Bar or section for use as a common junction between electrical circuits.



Metal taken from the same melt in a furnace or crucible, or of several melts mixed in the same furnace or crucible before pouring, or metal taken from a furnace without subsequent addition (when a continuous melting process is used). In the case of continuous or semicontinuous casting procedures this is also regarded as the product of a cycle up to 24hr where the same alloy and shape is cast.

Cast, Heat, Melt
These terms are used interchangeably to refer to the product of a single melting furnace charge. Sometimes the furnace contents are tapped into two or more ladles when the product of each ladle may be called a separate cast. It is always assumed that the chemical composition of an entire cast will be uniform. This is described as the “cast analysis” on a Certificate of Conformity etc.
Chatter Marks

Chatter marks

Regularly spaced superficial transverse markings produced by vibration between the metal and the working surface during fabrication.

Chemical Brightening
A chemical treatment to improve the specular reflectivity of a surface.
Chemical Conversion Coating
The treatment of material with chemical solutions by dipping or spraying to increase the thickness of the natural oxide film on the surface or to build up an oxide film bearing chromates or phosphates
Chill Casting

A process in which molten metal is poured into a permanent mould and solidified.

Circumscribing Circle
A circle that will just contain the cross section of an extrusion, usually designated by its diameter.
Clad Material
Material that has a thin layer of Aluminium or Aluminium alloy metallurgically bonded to it usually by rolling, extruding or drawing. Most often it is used to provide a more corrosion resistant surface or to facilitate anodising.
Cold Compression

Working of forged material at room temperature under compression through the thickness in the solution treated condition immediately after quenching to relieve internal stresses caused by quenching, and to minimize distortion during machining.

Cold Working
The permanent alteration of shape or dimensions by plastic deformation at room temperature by, e.g., cold rolling, cold reduction, drawing, pressing, forming, bending, swaging, etc.. Cold working increases strength and hardness but reduces ductility.
Colour Anodising
Incorporation of colouring matter (dyes) into the film of anodised Aluminium during the anodising process.

An inward curvature across the width of a surface of a rolled or extruded product.

Strictly, this is the shift between the centres of the circles that are the Outside Diameter (OD) and Inside Diameter (ID/ Bore) of a round tube. Any such shift will cause a variation in wall thickness around the circumference of the tube, hence the tolerance on concentricity is determined by the wall thickness tolerance.
The key part of an extrusion press into which the billet is placed before extrusion. It is a hollow cylinder which is closed at one end by the die and at the other by the extrusion ram. It has to contain the substantial pressures generated during extrusion.
Controlled Stretching
Stretching, under controlled tension, of plate and shate products to a specified extension (percentage permanent set). It relieves internal stress and minimises distortion during machining as well as improving flatness and straightness.
Critical Quencing Rate
The minimum mean cooling rate from the solution treatment temperature necessary to retain the alloying constituents in solid solution and thus permit the alloy to meet specified mechanical property requirements in the precipitation hardened (aged) condition.


Deep Drawing
The forming of deeply recessed parts (such as beverage cans and hollow-ware) by means of plastic deformation of the material. As deep drawing does not uniformly cold work the blank there will be variations in the hardness and annealing response around the final part.
Deep Drawing Sheet
Sheet produced with specific characteristics that permit deformation by deep drawing – such as softness, high ductility and low tensile strength.
Delayed Ageing, Delayed Age Hardening
Retarding natural ageing by holding the alloy below room temperature. If the alloy is raised to room temperature then natural ageing will proceed at the expected rate.
Die Drawing
A CAD Drawing of the extrusion die showing exact detail of the shape of the profile.
Die Lines
Continuous longitudinal lines that are formed on extruded and drawn products by minor irregularities, or pick up, on the bearing surfaces of the die.
Die, Extrusion Die
The hardened steel aperture through which a heated extrusion billet is pushed to form an extruded profile shape. There are 3 types of die: Flat Die – For extruding solid shapes Porthole Die – For extruding hollow shapes – This leaves one or two ‘weld’ seams along the length of the extrusion so tube produced in this way is called Welded Tube. Flat Die with Mandrel – For extruding seamless hollow shapes and seamless tube
Differential Annealing
The localised heating of part of a blank so that only specific areas are annealed.
Diffusion (in clad material)
The migration of alloying elements from the core into the cladding layer during thermal treatment. This can be detrimental to the properties and behaviour of both the core and cladding.
Diffusion Staining
Patchy surface discolouration that can occur as a result of diffusion in clad material.
Direct Extrusion, Extrusion
The extrusion process in which a preheated billet is placed in the container and is pushed by the ram through the stationary die to form the extruded section.
Related Terms: Container
Directional Properties
Deformation by cold working causes changes to the grain structure and, sometimes, variations in mechanical properties across and along a work-piece. Properties measured along the direction of deformation are described as longitudinal, whilst those measured at a right angle to the direction of working are called transverse.
Drawing, Cold Drawing
The pulling of a work-piece through a fixed die at room temperature. It can reduce the size, change the cross section or shape, improve surface finish, improve tolerances or work-harden the material.
Drawn Tube
A hollow product of uniform wall thickness, produced by cold drawing.
Drift Test, Flaring Test
A test for the weld integrity of a welded tube, usually carried out to BS1139. All batches of Scaffolding Tube undergo this test.
Related Terms: Scaffolding Tube
Duplex Ageing
A two stage age-hardening heat treatment conducted at different temperatures.
Dye Penetrant Test
A non-destructive test for surface defects and flaws. A clean and degreased work-piece is dipped in, or otherwise coated by, a fluid containing a brightly coloured dye. This fluid is often called dye penetrant ink. After a predetermined time the ink is removed, usually by washing, and a, usually white, developer applied. The dye seeps out from any flaws and cracks, thereby making them easily visible.


A pure chemical substance that consists of just one type of atom as defined by its atomic number (the number of protons in its nucleus). Elements combine to make compounds, e.g. Copper Sulphate which contains Copper, Sulphur and Oxygen. An Alloy, e.g. Brass, is a solid solution of two or more elements.
The production of a uniform matt, surface finish on a work-piece by controlled chemical or electrochemical attack. The etching agent can be either acid or alkali in nature.
Etching Test
The use of a chemical reagent to reveal the macrostructure of a sample from a work-piece. The test is usually made on a cross section from the work-piece so is destructive.
Extrusion Ratio
The ratio of the cross-sectional area of the extrusion container to that of the extruded product.


Narrow strip in the thickness range 0.2mm to 0.4mm used for finning of heat exchanger tubes in applications such as air conditioning.
Fixed Mandrel
A device for producing hollow extrusions of regular cross section. The tapered mandrel is attached to the main extrusion ram and passes through the hollow billet. As the ram moves forward the mandrel passes, with the billet, through the die giving a product slightly tapering in wall thickness along its length. The mandrel is tapered to facilitate its removal when extrusion is complete.
Flash Annealing
Annealing of a work-piece by rapid heating and a short dwell time at the appropriate temperature.
The property of having a horizontal surface without any slope, tilt, or curvature, i.e. that of a flat plane. In practice a perfectly flat surface is probably unobtainable so there will be a flatness tolerance.
Related Terms: Flatness Tolerance
Flatness Tolerance
A three-dimensional geometric tolerance that controls how much a product surface can deviate from a flat plane. The permitted deviation will depend upon the thickness of the sheet or plate varying between 0.2% and 0.5% of its width and length, usually measured over a 1 metre length.
Floating Mandrel
A tapered mandrel that is inserted into the hollow extrusion billet. It is not attached to the extrusion ram so is left free to centre itself in a hollow billet as it moves forward through the die as the ram advances and extrusion proceeds. The resulting product tapers slightly in wall thickness along the length.
Related Terms: Fixed Mandrel
Foil, Tin Foil, Kitchen Foil, Cooking Foil
Cold rolled aluminium flat product less than 250 microns in thickness. Usage includes kitchen foil (cooking foil) and foil trays for food. Kitchen Foil is often incorrectly referred to as Tin Foil.
Hot working using a forge with shaped tools that ‘hammers’ the work-piece into a predetermined shape.
Fracture Test, Impact Test, Charpy Test, Izod Test
A test in which the test piece is notched and broken. The fracture surface examined to assess grain structure and freedom from defects. Also used to determine toughness, often at varying temperatures to establish at what reduced temperature the material becomes brittle.
Free Machining Alloy (FMA)
An alloy designed to give, when machined, small broken chips, lower power consumption, better surface finish and/or longer tool life. Chemical composition and microstructure both influence this property.
Full Heat Treatment
For alloys in the 2xxx, 6xxx, 7xxx and 8xxx series this is the heat treatment cycle consisting of solution treatment followed by artificial age hardening.


Gauge Length
In a tensile test this is the prescribed part of the cylindrical or prismatic portion of the test piece on which elongation is measured at any moment during the test. In particular, a distinction should be made between the following: ~ The original gauge length, i.e. the gauge length before the test is started. ~ The final gauge length – The gauge length after the test is completed and the test piece has fractured. The broken pieces are carefully fitted together to lie in a straight line so that it can be measured.
Grain Flow
Elongation of the grain structure in the direction of cold working.
Grain Growth
Coarsening of the grain structure that occurs under certain conditions of heating. It is generally undesirable and is deleterious.
Grain Size
A measure of the area or volume of grains in polycrystalline material. Grain size is reported in a number of ways 1. number of grains per unit of area or volume, 2. average diameter, 3. as a grain size number derived from area measurements and comparison with a standard chart.


Hall Heroult Process, Smelting
The main process used for the production of Aluminium metal whereby Alumina is dissolved in a salt bath of molten cryolite and subject to an electrolysis process. Often referred to as Smelting, this process uses very large amounts of electricity. Named after two scientists who developed the process independently of each other at around the same time.
Hall-Heroult Process
The main process used for the production of Aluminium metal whereby Alumina is dissolved in a salt bath of molten cryolite and subject to an electrolysis process. Often referred to as Smelting, this process uses very large amounts of electricity. Named after two scientists who developed the process independently of each other at around the same time – Hall, English and Heroult, French.
Hardness Test
A test conducted to measure Hardness. A load is applied to an indenter to press it into the surface of the test piece. The indenter can be either a ball of various standard diameters or a diamond of one of several specified geometric profiles. The result of the test is reported as a Hardness Number which is derived from either a measurement of the depth to which the indenter penetrates or from the surface area of the impression left by the indenter.
Hardness, Vickers Hardness, Brinell Hardness, Rockwell Hardness
The resistance of a metal to plastic deformation usually by indentation using a diamond or a hardened steel ball. There are various recongnised hardness scales including Vickers (VPN), Brinell and Rockwell. N.B. The empirical, but robust, relationship between hardness and tensile properties that applies in steels does not apply, and the steel tables must not be used for aluminium and its alloys. A less rigorous relationship has been established for some aluminium alloys but it is not widely used.
Heat Treatable Alloy
Any of the 2xxx, 6xxx, 7xxx and 8xxx series of wrought aluminium alloys whose mechanical properties can be increased by a solution treatment and age hardening heat treatment cycle.
Heat Treatment
The thermal processing of a work-piece specifically to alter its mechanical properties. It includes:- 1. Annealing to soften and improve ductility. 2. Solution treatment and precipitation hardening to increase strength. It does not include heating before hot rolling, forging or extrusion etc.
The structure of as cast semi finished products e.g. slab, extrusion billet or forging blanks is invariably chemically segregated - that is the alloying elements are concentrated locally rather than uniformly distributed within the microstructure. Homogenising is a way of mitigating this as the work-piece is held at a suitably high temperature for sufficient time to eliminate, or at least decrease, chemical segregation by diffusion of the alloying elements.
Hot Working
Plastic deformation, e.g. hot rolling, extrusion or forging, of a work piece in a temperature range and at a rate such that strain hardening does not occur.


Indirect Extrusion, Backwards Extrusion
The extrusion method in which there is no relative movement between the billet and the container. This is accomplished by:- Either pushing the die held on the end of a long, hollow, stem through the billet. Or moving the billet and container together over the die, again held on the end of a long, hollow, stem. As there is no movement between the billet and container the friction, and hence extrusion loads, are reduced by up to 30% compared to direct extrusion and grain structures can be improved. The process is limited by the size, length and strength of the stem which holds the die.
A cast product that may be various shapes including slab, billet, bloom or more complex shapes. Produced by pouring liquid aluminium into a shaped mould and allowing it to cool.
Integral Colour Anodising
Coloured surfaces developed either by anodising certain Aluminium alloys and/or by using special organic electrolytes that produce colours during anodising.
Internal Stress
Stresses within a work-piece caused by previous treatments, e.g. casting, thermal treatment or fabrication.
Isothermal Quenching
A procedure in which the work piece is quenched, and held for some time, in a fluid which is held at a constant temperature between the solution treatment temperature and room temperature. This permits precipitation hardening.


Lateral Curvature, Edge Curvature
The lateral departure, in arc form, of an edge from linear straightness.
Lüders Lines
Surface marks caused by localised flow that appears on some alloys after light straining. They run parallel to the direction of maximum shear stress i.e. at 45° to the direction of the deforming stress.


Mean Diameter
The sum of any two diameters at right angles divided by two.
Mean Wall Thickness
For a tube this is the sum of four wall thickness measurements, made at 90o intervals around the diameter, divided by four.
Multi-Hole Die
An extrusion die, with more than one hole, allowing multiple extrusions to be made simultaneously from one billet.


Natural Ageing
The process that can alter the hardness and strength in some alloys after a period of time at ambient (room) temperature. It is caused by the spontaneous precipitation of constituents from a super-saturated solid solution. Generally it increases mechanical properties but can also, in some circumstances, cause loss of properties by over-ageing.
Related Terms: Over-ageing
Non-Heat Treatable Alloy
An alloy, from the 1xxx, 3xxx and 5xxx series that are incapable of being strengthened by thermal treatment. These alloys gain their strength from cold-working.


Oil Staining
Surface staining caused by the partial decomposition during thermal treatment of residual lubricant.
Orange Peel
A roughening, on subsequent cold deformation, of the surface of sheet or strip when the grain size is too coarse. Has the appearance of an orange skin.
Bauxite - A red rock found in the earth's crust, close to the surface. Extracted by open-cast mining it is a very rich ore with a 25% yield.
Any variation from a true circle of the cross section of a round tube, bar or wire.
Artificial ageing treatment at too high a temperature, or for too long a time, after the maximum hardening effect has been achieved. It causes some loss of properties. In some cases it may be a deliberate act, e.g. to improve resistance to stress corrosion or to minimise any further loss of properties in alloys operating at higher temperatures.


Partial Annealing
Thermal treatment, after cold working, of a work-piece to reduce its strength to a controlled, but not fully softened, level.
Percentage Elongation after Fracture (A)
The gauge length elongation after fracture expressed as a percentage of the original gauge length.
Peripheral Coarse Grain, Peripheral Grain Band
An effect shown in extruded products and also forgings made from extruded stock. It is an area of recrystallised grains at the periphery which has lower properties than the non-recrystallised core.
Irregular surface roughness or damage caused by adhesion and subsequent fracture or tearing between the forming tools and the work piece.
Pips, Pip Lines, Pip Marks, Ident Pips
A marking on an extrusion (on a non-visible surface) placed there by the extrusion mill’s die to allow the mill to identify extrusions produced by that mill.
Pitting Corrosion
Non uniform corrosion of the surface that causes small pits or craters to develop.
A hot rolled flat product of rectangular section, typically over 10mm thick. Control of surface finish is less rigorous than for sheet.
Related Terms: Sheet, Shate
Porthole Dies
Dies that produce extruded hollow products from solid extrusion ingots. They incorporate a mandrel as an integral part of the die assembly and leave one or two ‘weld’ seams along the extrusions.. Bridge, spider, duo and self-stripping dies are particular types of porthole die.
Powder Coating
Application of an even layer of colour to aluminium extrusions by spraying powdered paint using an electrostatic process then baking on (stove enamelling).
A thermal treatment after quenching and before the end of the precipitation incubation period.
Precipitation Annealing
The heating of a quenched and precipitation hardened work piece for some time at a temperature between the artificial ageing temperature and the solution treatment temperature. It produces significant softening by coalescing the hardening precipitates.
Pressure Test
A hydraulic or pneumatic test for tubes to prove that they material can withstand a specified pressure for a specified time without leakage or rupture.
Proof Stress (Rp)
The stress or applied load which produces a permanent elongation equal to a specific percentage of the original gauge length. In alloys that do not exhibit a yield point it is used as an equivalent to the elastic limit. If a proof stress is specified, the non-proportional elongation must be stated. The most common values used in specifications is 0.2% or 1.0% and the RP symbol used for the stress will be supplemented by an index giving this prescribed percentage of the original gauge length, e.g. RP0.2 = 0.2% Proof Stress


The rapid cooling a metal or alloy from the solution treatment temperature by contact with a solid, a liquid or a gas to retain the hardening constituents in solid solution. Quenching is often carried out by immersion in cold water. Extrusions are quenched after extrusion by air blasts.


Recrystallisation Annealing
A heat treatment that softens a cold worked metal or alloy by complete recrystallisation.
Work done to correct dimensional errors.
Residual Stress
Any stress in a finished product after fabrication (mainly cold work) which exists without the presence of any service or external loads, even after stress relieving.
Roller Levelling, Tension Levelling
Flattening of sheet, strip or coil metal by passing it through a roll train staggered rolls. Levelling is achieved by precisely bending metal strip back and forth as it's passed through a series of small-diameter offset rolls. The material is usually also under tension loading.
Roller Straightening
The straightening of extrusions by passage through a series of small diameter, staggered, rolls.


Scaffolding Tube
A ‘welded’ tube, size 1 29/32 inch O/D x 7 swg wall thickness (7swg = 0.176 inch / 4.47mm) used for scaffolding that has been Drift Tested
Mechanical removal of oxide and contamination from surface of a cast slab prior to hot rolling.
Sealing of Anodic Coatings
A post anodising treatment to close layer porosity and reduce absorbency.
The non uniform distribution in the microstructure of alloying elements during the solidification of an ingot, billet or slab. Some non metallic impurities may also be segregated during solidification.
Self-Quenching Alloy
An alloy whose critical quench rate from its solution treatment temperature is slower than the rate of cooling in still air. This means that the alloying elements will be held in solid solution even after cooling in still air.
A term used for rolled material where the thickness lies between that of cold rolled sheet and hot rolled plate, typically 4 to 10 mm. the finish may be hot or cold rolled.
Shear Strength
The maximum stress that a material can sustain when loaded in shear. As a very rough guide for aluminium alloys the maximum shear strength is about 60 to 65% of the ultimate tensile strength and the yield strength in shear is 50 to 55% of the 0.2% Proof Stress.
Shear Test
A test in which the test piece is progressively loaded to fracture in shear to measure its shear strength.
Usually defined as cold rolled flat product in the thickness range 0.25mm to 3.25mm.
Short Transverse Direction
The minor axis at right angles to the major, longitudinal, axis.
Single-Hole Die
An extrusion die with one hole, therefore capable of producing just one extrusion per cycle.
Related Terms: Multi-Hole Die
Slab, Rolling Slab
A cast product that will be used for hot rolling. Size up to 300mm thick, 2000mm wide and 10/15 metres long with weight up to 15 tonnes.
The simultaneous cutting of a coil or wide strip into a number of narrower strips by means of rotary cutters.
Stop Mark
A transverse peripheral ridge on a product arising from a stoppage during rolling, extrusion or drawing.
Strain Hardening, Work Hardening
The increase in strength and hardness with a general loss of ductility that results from cold working of a work-piece.
Related Terms: Cold Working
Streching, Stretcher Levelling
A term used to describe both the levelling of rolled materials and the straightening of extruded and drawn materials by imparting sufficient permanent extension to remove distortion.
Stress Corrosion
This is the frequently rapid, sudden, failure of normally ductile alloys when experiencing tensile stresses in certain and specific corrosive environments. These stresses may be residual internal stresses or from external loading.
Stretcher Grip Marks
Transverse indentations left by the gripper jaws of the stretching machine on the ends of a product.
Stretcher Strain Markings
These are permanent surface distortions that can occur on stretching. They can appear as either flamboyant patterns or Lüders lines. Their onset and extent depends on the type of material and the degree of stretching.
Super Annealing
An annealing cycle for heat treatable alloys that utilises a slow, controlled, cooling rate to produce a structure with maximum ductility and the minimum tendency to natural ageing.
Surface Bloom
A general term for any surface discolouration caused by thermal treatment or from exposure to moist atmospheres.


The characteristic structural and mechanical properties produced by mechanical working and/or thermal treatments.
Related Terms: Temper Designations
Temper Designations
There are two systems of letters and digits used, after the alloy designation number, to define and describe the temper of an aluminium alloy. The following is only an outline guide to these systems. For the strain hardening alloys of 1xxx, 3xxx and 5xxx series the following is used:- O = Annealed, soft F = As Fabricated H1x = Strain Hardened only H2x = Strain Hardened and partly annealed. H3x = Strain Hardened and stabilised H4x = Strain Hardened and organically coated with an oven cure. The second number shown as x above indicates the final degree of hardness or strength. 2 = quarter hard 4 = half hard 6 = three quarter hard 8 = fully hard. For the heat treatable alloys of the 2xxx, 6xxx,7xxx and 8xxx series the following applies. T1 = cooled from a high temperature forming process and naturally aged. T2 = cooled from a high temperature forming process cold worked and naturally aged. T3 = solution treated, cold worked and naturally aged. T4 = solution treated and naturally aged. T5 = cooled from a high temperature forming process and age hardened by heat treatment. T6 = solution treated and age hardened. T7 = solution treated and deliberately overaged T8 = solution treated, cold worked and age hardened T9 = solution treated, age hardened then cold worked. Additional numbers may also appear to indicate variations in treatment that can significantly influence the condition of the alloy.
Temper Rolling
A controlled cold rolling procedure performed to develop specific mechanical properties in a work piece.
Tensile Strength, Ultimate Tensile Strength (UTS)
The maximum load, in tension, that a material can withstand before breaking. It is calculated as a breaking load for a standard cross section area.
Tensile Test
A procedure to measure the mechanical properties of a representative test piece in tension. The test piece is progressively loaded in tension and its gauge length plotted against the applied load generally to the point of fracture. The Proof Stress (Rp) and Tensile Strength (Rm) values are then determined.
The permissible limit, or limits, of variation to a specified parameter such as a dimension or weight, usually expressed as 'plus' or 'minus' value or percentage on that quantity.
Torsion Test
A test in which a sample is twisted axially for a given number of revolutions. It may be conducted to destruction or to demonstrate that the material can withstand a specific amount of twisting.
Traffic Marks, Fretting
Abrasions, usually dark in colour, resulting from relative movement, or rubbing, between contacting metal surfaces during transit.
Transition Joint, Triplate
An explosively bonded bimetal flat bar that comprises a layer each of steel and marine-grade aluminium (alloy 5083) usually with an interlayer of pure aluminium. It is used for the on site welding of aluminium to steel, especially in shipyards and for offshore structures.


Ultrasonic Test
A non-destructive test method using ultra high frequency sound waves to locate and assess the size of internal material defects.
An artificial ageing treatment that fails to achieve maximum or optimum increase in mechanical properties/hardening. It is caused either by processing for an insufficient time or at too low a temperature.
Upper Critical Strain
The minimum amount of cold work needed prior to annealing or solution treatment to produce a fine recrystallized equiaxed grain structure by eliminating the cold worked structure of elongated grains.


Water Staining
A residue left on aluminium that has been wet and allowed to dry naturally. This is very difficult to remove and cannot be improved by polishing or anodising.
Wrought Product
A product made by hot, or hot and cold, plastic deformation by the rolling, extruding or forging of a cast product.