Aluminum is a lightweight, soft, low strength metal which can easily be cast, forged, machined, formed, and welded. It is suitable only in low temperature applications, except when alloyed with specific elements. Commercial aluminum alloys are classified into two groups, wrought alloys and cast alloys. The wrought alloy group includes those alloys which are designed for mill products whose final physical forms are obtained by working the metal mechanically. The casting alloy group includes those alloys whose final shapes are obtained by allowing the molten metal to solidify in a mold.
Uses. Aluminum is used as a deoxidizer and alloying agent in the manufacture of steel. Castings, pistons, torque converter pump housings, aircraft structures, kitchen utensils, railways cars, and transmission lines are made of aluminum.
Capabilities. Aluminum can be cast, forged, machined, formed, and welded.
Limitations. Direct metal contact of aluminum with copper and copper alloys should be avoided. Aluminum should be used in low-temperature applications.
Properties. Pure aluminum has a Brinell hardness number of 17 to 27; tensile strength of 6000 to 16,000 psi (41,370 to 110,320 kPa); specific gravity of 2.7; and a melting point of 1220°F (660°C). Aluminum alloys have a Brinell hardness number of 100 to 130, and tensile strength of 30,000 to 75,000 psi (206,850 to 517,125 kPa). Generally, aluminum and aluminum alloys have excellent heat conductivity; high electrical conductivity (60 percent that of copper, volume for volume; high strength/weight ratio at room temperature; and unfairly corrosion resistant.
Appearance test. Aluminum is light gray to silver in color, very bright when polished, dull when oxidized, and light in weight. Rolled and sheet materials are usually pure metal. Castings are alloys of aluminum with other metals, usually zinc, copper, silicon, and sometimes iron and magnesium. Wrought alloys may contain chromium, silicon, magnesium, or manganese. Aluminum strongly resembles magnesium in appearance, it is distinguished from magnesium by the application of a drop of silver nitrate solution on each surface. The silver nitrate will not react with the aluminum, but leaves a black deposit of silver on the magnesium.
Fracture test. A fracture in rolled sections shows a smooth, bright structure. A fracture in an aluminum casting shins a bright crystalline structure.
Spark test. No sparks are given off from aluminum.
Torch test. Aluminum does not turn red before melting. It holds its shape until almost molten, then collapses (hot shorts) suddenly. A heavy film of white oxide forms instantly on the molten surface.