Glossary


Annealing– a thermal treatment used to soften the metal by removal of stresses from cold working or by coalescing precipitates from solid solution. When the metal is fully softened it’s called a full anneal. When only some of the stresses are removed it’s called a partial anneal. In the latter case, the metal is stronger but less ductile than in the case of a full anneal.

Brinell Hardness – One of several systems that serve to measure a metal’s resistance to mechanical indentation. There are other hardness testing devices, but the Brinell equipment provides the readings most commonly found in aluminum publications. With the Brinell machine, a piece of aluminum is placed on an anvil and subjected to 500 kilograms of pressure by a 10-millimeter ball in contact with its upper surface. This pressure is maintained for 30 seconds, released, and then the operator, using a direct read from the equipment’s dial indicator, determines to what degree the metal resisted penetration by the ball. The number attained is known as the BHN (Brinell Hardness Number).

Common Alloys – One of several terms used in the industry to identify the non-heat-treatable classes of alloys – alloys identified in the four-digit numbering system by having as their first digit a “1”, a “3”, a “5”, or in some cases an “8”. This category of alloys has its strength levels increased by being subjected to some type of cold-working processes such as rolling, drawing, or stretching, but not through any of the thermal processes. Exposure to temperatures above rather low levels can only reduce the strength of the non-heat-treatable or common alloys.

Conversion coatings – Proprietary solutions, usually of a chromate or phosphate variety, which, when applied to a clean aluminum surface will serve to increase the metal’s resistance to corrosion and provide a good base for paint adhesion. Conversion coatings can also help enhance the aesthetic of aluminum products.

Corrosion – The deterioration of material due to its reaction to its environment. Depending upon the type of corrosive conditions, the deterioration may be staining, pitting, flaking or, in very severe cases, fracturing – particularly if the metal is under stress.

Elongation – One of the mechanical properties of aluminum, i.e., the ability of the metal to stretch, or elongate, when it is subjected to an applied stress. The distance the metal will stretch from the point where yielding begins to the point where the metal fractures is expressed as a percentage figure and is known as the elongation. This is one of the factors that is often considered when planning to bend, form, draw, or stretch metal.

Embossed/Patterned Sheet – This product is produced by passing coiled sheet through a pair of steel rolls that have a repeating pattern machined, or etched, on their surface. Based on roll configuration, pressure on the rolls transmits the embossments or indentations to the surface of the sheet. The pattern may be one or two-sided.

Gauge/Thickness – Both terms are in common use, but the latter is preferred when describing the thickness of a wrought product.

Ingot – A cast form of the metal that is suitable for remelting or fabricating. The ingot may take the form of rolling ingot, extrusion ingot, forging ingot or remelt ingot. The size and shape of the cast product will be designed to facilitate the subsequent operations. For example, a remelt ingot may weigh as little as 50 lbs while a rolling ingot could go as high as 40,000 lbs.

Mechanical properties – Those properties associated with the material’s reaction when force is applied, or that involve the relationship between stress and strain. This would include tensile properties, modulus of elasticity and endurance limit.

Master/parent coil – A large coil to be slit into two or more smaller coils to meet customer width requirements.

Rockwell hardness – Another of the methods used to determine a metal’s resistance to indentation. Rockwell equipment is more widely used than the Brinell equipment and many more testers of aluminum will refer to the Rockwell system. There are charts available to convert from one system to the other.

Slitting – A high-speed method of cutting sheet in coiled form to narrower width coils. Although there are flat sheet slitters in existence, most machines will only accommodate coiled products. Two circular knives, one above and the other with clearance between their edges determined by alloy strength and thickness are required for each cut to be made. The knives are located on parallel spindles, and, with the proper clearance set, produce a clean accurate cut as the sheet passes through them. Material is payed off a coil at the head of the line, travels through the slitter knives, and is rewound into new coils at the end of the line. Normally, slitting is the last mechanical operation performed on the metal before it leaves the mill.

Ultimate tensile strength (UTS) – Another common term to describe mechanical strength. This metal property is expressed in thousands of pounds per square inch and denotes how much stress can be gradually applied to the metal before it fractures. Tensile testing is done by pulling two ends of a test sample in opposite directions under a constantly increasing force, subjecting the product to stress. The stress is measured until the product is pulled in two. The measurement at the exact time of fracture is the material’s ultimate tensile strength.

Water stain – If oxygen is excluded from the wraps of coiled product, from the inner surfaces of stacked flat products, or from the faying surfaces of extruded products, and should moisture be permitted to enter those areas through condensation or water exposure, the moisture will have the tendency to steal the oxygen from the skin of aluminum. When this happens, the surface of the metal will become roughened and eventually pitted unless the water is removed and those surfaces are kept exposed to the air or kept free from further moisture. Although water stain is usually only an aesthetic complaint, it can become severe enough to become a structural problem by reducing metal thickness. Aluminum users should learn and practice the basic rules for the handling and storing of aluminum.


Webster hardness
– Another method used to determine resistance to indentation and thereby estimate mechanical strength. The Webster tester is a hand-held, direct-read unit. Its degree of accuracy is somewhat below that of the Rockwell and Brinell equipment because it is portable and the data can be greatly affected by the skill and consistency of the operator. It can be used to determine if the heat-treatable alloys have received their scheduled thermal treatments, and many customers use the Webster as a guide to a metal’s formability based on internal standards they have established. In this latter instance, a customer may have decided that an extruded product must fall between the 10 and 13 range on a Webster to meet bending or forming requirements, and, with that standard agreed to by the producing mill, will let the criterion serve for acceptance or rejection of shipments.


Yield tensile strength (YTS)
– A property of the material that describes the stress at which the material exhibits a specified permanent set. That is the point at which it will not spring back to its original length when stress on the material is relieved. For aluminum the yield strength is usually measured at the point where the stress applied to the material causes a 0.2% (of the gauge length) permanent set.