|Aluminum Technical Data/Definitions of Terms|
AGING- A reaction of the alloying elements taking place in the heat treat-treatable alloys after solution heat-treatment that brings about an increase in hardness and strength with a decrease in ductility. The reaction may occur at room temperature and is then defined as natural aging, but the speed of the reaction can be accelerated if it takes place at an elevated temperature in the 250 to 450 degree Fahrenheit range where it is identified as artificial aging.
ALCLAD/CLAD- Both terms relate to a composite material having a relatively thin sheet of higher purity or anodic alloy metallurgically bonded to a core alloy. Bonding takes place during the first pass through the hot line breakdown rolling mill. These thin sheets may be put on one or two sides depending upon customer requirements. If the skin is applied to the core to increase the corrosion resistance of that core, the composite is said to be Alclad material. If, however, the purpose of the outer skin or skins is to offer that core a characteristic other than corrosion resistance such as a superior surface or a surface that is suitable for brazing, the end product is said to be Clad material.
ALODIZING- A proprietary term that applies to the application of an Amchem products solution known as Alodine- merely one of several types of conversion coatings. Alodizing is included here because it is often confused with a very different process-ANODIZING.
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 latter case, the metal is stronger but less ductile than in the case of a full anneal.
ANODIZING- Like most metals, aluminum, when exposed to the atmosphere, will attempt to revert to its natural state by reacting with the oxygen in the air, thus creating an oxide film on its surface. In the case of steel, the film or more accurately the coating that forms will be ferric oxide, or rust. This coating may flake off, actually reducing metal thickness which may be detrimental to the service life of the steel. On the other hand, aluminum's oxide adheres tightly to the surface and serves to protect the metal in the air and in most neutral or mildly acidic or alkaline solutions. Nature's film is a bit on the skimpy side at five millionths of an inch (.000005") thick so it is somewhat limited in its ability to resist corrosive attack under certain conditions. However, the oxide film can be made thicker, increasing its corrosion resistance and wearability. This is done by putting the aluminum into a sulfuric acid bath and then passing an electrical current through the solution which serves as an electrolyte. The result is an anodized product. The process does what nature would do, but it is done much faster; and, with controlled operating parameters, a film is created which is much thicker than nature would provide.
BAR- A solid section of metal that is long in relation to it's cross section, which is square, rectangular (excluding plate), or is a regular hexagon or octagon, and in which at least on perpendicular distance between parallel faces is 0.375 inches or greater.
BEND RADIUS (Recommended minimum)- A rule of thumb type of measurement of a material's ability to adapt to bending to a 90 degree inside angle using a "vee" press brake die. Taking into consideration a particular metal's mechanical properties and it's thickness, the bend radius charts will serve to tell how sharp a bend can be made in metal without it fracturing on the outside of the bend. These charts set down recommended minimum inside bend radii. it is suggested that one fabricate to an inside radius slightly larger than the one specified. It is important that the fabricator realize that the bend radius charts are valid only if the forming is classified as an air bend and the metal does not bottom in the die/
BILLET- The raw material form for an extrusion press. a cylindrical length of cast aluminum which, after preheating to a specified temperature, will be loaded into the press container and forced through a steel die opening to exit the press having assumed the shape of that die opening.
BRIGHT DIP- Like caustic etch, this is a pretreatment for aluminum to be anodized. The bright dip process, using a phosphoric acid bath, will brighten and increase the reflectivity of the aluminum surfaces in contacts. Because of waste disposal restrictions, this process is not as popular as it once was, but it is still used for the finishing of appliance trim, jewelry, etc.
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).
CAUSTIC ETCH- Like the bright dip, caustic etch is pretreatment for anodizing. The anodic film is transparent and exposes the as-received surface of the aluminum which may not be pleasing to the eye. By subjecting the bare, clean aluminum to a caustic bath, the surface of the metal will be minutely eaten away and leveled. The resulting soft frosted, or matte, appearance is consistently attractive under the anodic film.
COLD FINISHED- Rod or bar brought to a final diameter or thickness by means of a cross section reduction applied to the metal when it is at room temperature. Examples are cold rolling, cold drawing or cold extruding.
COLD WORKING- Material reduction or deformation carried on at temperatures below those resulting in the recrystallization or annealing of the metal. Cold working of the metal will bring about strain-hardening with an increase in strength and hardness. Cold worked metal may have its strength level reduced by partial annealing, or may have it brought down to its lowest level by full annealing.
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- (See Alondizing) 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. In addition, some manufacturers use conversion coatings to enhance the aesthetics of their products.
CORROSION- The deterioration of a 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.
ELECTRICAL CONDUCTIVITY- One of the physical properties of aluminum. It denotes the ability of a particular temper of a particular alloy to carry electrical current. All published ratings, shown as a percentage, are based on the conductivity of copper which carries a 100 percent rating, thus is the standard. As an example, based on data available, 6061-T6 will have a conductivity rating of 43 percent when it is compared to a copper product having the same overall dimensions. If however, we are to take density into consideration and compare that 6061-T6 product to a copper product equal to it in weight, the conductivity of the aluminum item would jump to 142 percent.
ELONGATION- One of the mechanical properties of aluminum, i.e., the ability of the metal to stretch, or elongate, when it is subject 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/PATTERENED 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.
EXTRUDED SHAPES- Continuous lineal shapes produced by forcing a preheated billet into and through an orifice, or opening, in a steel die under great pressure, thus causing the metal to assume the shape of that opening. Oversimplified, it might be likened to squirting icing through various shaped openings with a cake decorating gun.
FINISHING- A broad classification denoting production operations performed on a material to alter its appearance, to improve its corrosion resistance, to enhance its aesthetics, or to prepare it for some special application. Mechanical finishing includes buffing, polishing, grinding, sanding, or even subjecting a surface to sand or shot blasting. Chemical finishing includes preparation for painting or anodizing with conversion coating. Caustic etching and bright dipping are examples. Electrolytic finishing covers any of the various anodizing processes. Applied finishing involves painting, laminating, plating or porcelainizing.
FOIL- Foil is simply a thin-gauge sheet product .0059" or less thick with a limited availability of alloys and tempers. The foil alloys are primarily made up of the week, high-purity types perfectly suited for wrap, containers, labels, etc. To produce foil products, the aluminum is processed as it would be for sheet products and then rolled and reduced in thickness or special foil mills.
FORGING- The more common type forging is the die forging which is produced when prefigured volume of hot metal is allowed to flow into a solidly fixed steel cavity. The cavity is capable of being raised and lowered to close on the bottom section. The top and bottom halves of the cavity are filled with hot metal; then the upper section, or die, is brought down to a closure using tremendous force. A forged sphere, for example, would result when a proper mass of hot metal is forced between hemispherical voids in the top and bottom dies.
FORGING STOCK- A mill-produced rod, bar or special shaped piece of metal that is suitable after heating for forging. Forging stock is usually supplied in the "F" temper because it will be annealed as it is heated for forging.
HEAT TREATING- Normally used to describe a process where metal is heated at a high enough temperature to put soluble elements into solid solution. This is by cooling the metal rapidly enough to retain the elements in solid solution. Often a separate heating operation (artificial aging) will be used subsequently to further strengthen the material.
IMPACTS- This class of products is also called impact extrusions. There are two basic production methods and both use a flat slug of metal as their starting material. By one method, the slug is forced to fill a void in the die as in a forging operation but, usually, on a smaller scale. By the second method, pressure forces the slug to flow upwards around a punch to assume a cylinder shape such as a toothpaste tube, an aerosol can ,or a fire extinguisher. Both operations are usually performed at room temperature.
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 pounds while a rolling ingot could go as high as 40,000 lbs.
MECHANICAL PROPERTIES- Those properties associated with 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 PLATE- A large plate product to be sheared or sawn into two or more smaller plates to meet customer width and length requirements.
NON-HEAT-TREATABLE ALLOYS- The correct and possibly the most definitive term for the 1XXX, the 3XXX, the 5XXX and some 8XXX alloy classes. These alloys gain strength through cold working and lose strength through thermal treatments. They are also called soft or common alloys.
PIPE- A tube whose outside diameter and wall thickness must conform to the industry standards governing the use of pipe products. In other words, there are standard pipe sizes, and potential users must select from those sizes and from no others. Seamless pipe, produced most often from hollow billet, has no seams or weld lines in its walls. The more popular structural pipe, the type produced by Kaiser aluminum, comes from a solid billet and has weld lines running longitudinally in the periphery because the metal flows around a plug, or mandrel, sin the extrusion die and rejoins itself as it exits the die. The latter product is not to be used in applications involving internal pressure, and one might encounter fabrication problems if it is subject to severe forming operations.
QUENCHING- A closely controlled rapid cooling of metal from some type of high temperature operation such as heat treating, casting, forging, or extruding. The cooling medium is usually water or air, or a combination of the two, and the purpose is to chill the metal quickly and lock the alloying elements into the dispersed positions imparted to them by the high temperature operation.
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.
SCALPING- The skin of an ingot is made up oxides and impurities that come from exposure to the environment, equipment, shops oils, dirt, etc. These impurities could be detrimental to the finished product's quality and integrity so, prior to the first working operation, the ingot is processed through a machining station where this outside skin is shaved off to a point where these impurities are removed from the working surfaces.
SCREW MACHINES- High speed types of machining equipment used in the manufacture of high production items such as bolts, pins, screws, fasteners and fittings are called screw machines. For this equipment, a limited number of alloys and tempers are produced to meet the stringent industry standards in regard to machining speed, surface quality, chip removal and tool life.
SHEARING- A machine action capable of reducing the width and/or the length of flat rolled products. The movement is similar to that of a paper cutter with a fixed bottom blade and a movable top blade. Material to be sheared is placed between the two blades against a fixed stop, the machine is activated, and the top blade moves downward shearing the material in two. The top blade then returns to its topmost position awaiting the next activation. Material is repositioned and recut as often as necessary to achieve the required dimension.
SHEET- Like plate, sheet is a flat rolled product which is rectangular in cross section, but it differed from plate in that it is thinner. Sheet thicknesses lie between those assigned to foil and those assigned to plate-over 0.0059 inches but less than 0.250 inches.
SLITTING- A high speed method of cutting sheet in coiled for to narrower width coils. Although there are flat sheet slitters in existence, most machines will only accommodate coiled products. Two circular knives, one above 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 the 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.
SOFT ALLOYS- Another of the terms given to the lower strength, common alloys. Soft is misleading because the 5xxx series is in the group and some of these alloys have fairly high mechanical properties. The 1XXX, 3XXX, 5XXX and most of the 6XXX alloy classes are all called soft alloys.
STABILIZING- A phenomenon peculiar to the 5XXX series, or magnesium-bearing alloys, which tend to age soften during storage. The resultant lowering of mechanical properties may cause the metal to be below spec when the customer uses it. To prevent this, most of these products are subject to low temperature thermal treatment before they are shipped from the mill. the result of this treatment is a slight drop in the metal's yield tensile strength to a stable level that is no longer subject to age softening.
STRESS RELIEVING- Regardless of product form, mill processing subjects aluminum to varying degree of deformation cause by hot and cold temperature espouser, inconsistent and unbalanced stresses, etc. The result of all this is hidden internal stresses within the products which can distort the metal or its surface is removed. Should the ultimate user plan to remove large amounts of metal, do extensive machining or perform a myriad of other critical processes, the metal might go completely beyond the acceptable degree of flatness or shape. To circumvent this, the mills are equipped to stress-relieve metal that is targeted for those types of operations by stretching, compressing, or thermal processes-depending on product form, alloy and temper.
TUBE- A hollow wrought product that is long in relation to its cross section, is round, hexagonal, octagonal, elliptical, square, or rectangular with sharp or rounded corners, and has uniform wall thickness except as affected by corner radii. Like pipe, tube may or may not have seams or welds depending on the method of manufacture.
TREAD SHEET AND PLATE- This product has a raised one side diamond embossed pattern impaired by mill rolls to provide improved traction. It is of misidentified as "Tread Sheet", belying the fact that it is commonly produced in plate thicknesses also. For years, 6061 was the standard alloy for this product, but several of the non-heat-treatable alloys are now also available in this pattern. The latter, under the heading of "Tread Bright", find applications where aesthetics is more important to the user than strength.
ULTIMATE TENSILE STRENGTH(UTS)- Another common term to describe mechanical strength. This metal property is expressed in thousands of pounds per square inch and denote show 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 materials 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 the 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 stains 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.(See "handling and Storing Aluminum" in this section. Several publication are available on this subject.)
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 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 an 13 range on a Webster to meet bending or forming requirements, and, with that standard agreed to by the producing mill, will let that criterion serve for acceptance or rejection of shipments.
WIRE- Here is the "W" in the often seen RBW heading. A definition of wire is just about the same as the definition for bar, in that wire can be almost any cross section, but, unlike bar, wire can be round. The major difference lies in the fact that the minor dimension for bar must be at least three-eighths of an inch (.375") while the major dimension for wire must be under three-eighths of an inch.
WIRE, COLD-HEADING- This is a wire product with a make up and quality suitable for use in the manufacture of cold-headed items such as rivets and bolts.
YEILD 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 a0.2% (of the gauge length) permanent set.