Commercial aluminum alloys are grouped into two classifications: wrought alloys and cast alloys.
Wrought Alloys
Wrought alloys are those alloys which are designed for mill products for which final physical forms are obtained by mechanical working, such as rolling, forging, extruding and drawing. Wrought aluminum mill products include sheet, plate, wire, rod, bar, tube, pipe, forgings, angles, structural items, channels, and rolled and extruded shapes.
Cast Alloys
Cast alloys are those alloys which are shaped into final form by filling a mold with molten metal and allowing it to solidify in the mold.
Sand Casting
Sand casting utilizes a mold in sand made around a previously formed pattern to the exact shape desired in the final casting, but slightly larger in size to allow for shrinkage of the cast metal as it cools.
Permanent Mold Castings
Permanent mold castings are made by pouring molten metal into steel or iron molds.
Die Castings
Die castings are also made in steel molds, but the molten metal is forced under pressure into the die or mold cavities. Die casting yields a denser casting with a better surface finish, closer dimensional tolerances, and thinner sections when desired.
Clad Alloys
Clad alloys, which may be up to 5% of the total thickness on each side, yield a composite product which provides the high strength of the core alloy protected by the cladding. Copper and zinc, when used as major alloying elements, reduce the overall resistance to corrosion of aluminum alloys. To gain the desired corrosion resistance in these alloys in sheet and plate form, they are clad with high purity aluminum, a low magnesium-silicon alloy, or an alloy of 1% zinc.
Wrought Alloy Designations
The Aluminum Association, an organization composed of manufacturers of aluminum and aluminum alloys, has devised a four-digit index system for designating wrought aluminum and wrought aluminum alloys. The first digit indicates the alloy group, ie; the major alloying element, as shown in Table A-2. The second digit indicates a modification of the original alloy, or the impurity limit of unalloyed aluminum. The third and fourth digits identify the alloy or indicate the aluminurn purity. See UNIFIED NUMBERING SYSTEM.
Wrought Alloy Temper Designations
In this index system, the letter following the alloy designation and separated from it by a hyphen indicates the basic temper designation. The addition of a subsequent digit, when applicable, refers to the specific treatment used to attain this temper condition.
Alloys which are hardenable only by cold working are assigned “H’ designations; alloys hardenable by heat treatment or by a combination of heat treatment and cold work are assigned “T” designations. Table A-3 shows the basic temper designations and resulting condition of the alloy.
Casting Alloy Designations
A system of four-digit numerical designations is used to identify aluminum casting alloys, as shown in Table A-4. The first digit indicates the alloy group, the second two digits identify the aluminum alloy within the group, and the last digit (which is separated from the first three by a period) indicates the product form. A modification of the original alloy or impurity limits is indicated by a letter before the numerical designation. The temper designation system for castings is the same as that for wrought product shown in Table A-3.
