Magnesium is an extremely light metal, is white in color, has a low melting point, excellent machinability, and is weldable. Welding by either the arc or gas process requires the use of a gaseous shield. Magnesium is moderately resistant to atmospheric exposure, many chemicals such as alkalies, chromic and hydrofluoric acids, hydrocarbons, and most alcohols, phenols, esters, and oils. It is nonmagnetic. Galvanic corrosion is an important factor in any assembly with magnesium.
Uses. Magnesium is used as a deoxidizer for brass, bronze, nickel, and silver. Because of its light weight, it is used in many weight-saving applications, particularly in the aircraft industry. It is also used in the manufacture and use of fireworks for railroad flares and signals, and for military purposes. Magnesium castings are used for engine housings, blowers, hose pieces, landing wheels, and certain parts of the fuselage of aircraft. Magnesium alloy materials are used in sewing machines, typewriters, and textile machines.
Capabilities. Magnesium can be forged, cast, welded, and machined.
Limitations. Magnesium in fine chip form will ignite at low temperatures (800 to 1200°F (427 to 649°C)). The flame can be mothered with suitable materials such as carbon dioxide (CO2), foam, and sand.
Properties. Pure magnesium has tensile strength of 12,000 psi (82,740 kPa) (cast) and tensile strength of 37,000 psi (255,115 kPa) (rolled); Brinell hardness number of 30 (cast) and 50 (rolled); specific gravity of 1.7; and a melting point of 1202°F (650°C). Magnesium alloy has Brinell hardness number of 72 (hard) and 50 (forged); and tensile strength of 42,000 psi (289,590 kPa) (hard) and 32,000 psi (220,640 kPa) (forged).
Appearance test. Magnesium resembles aluminum in appearance. The polished surface is silver-white, but quickly oxidizes to a grayish film. Like aluminum, it is highly corrosion resistant and has a good strength-to-weight ratio, but is lighter in weight than aluminum. It has a very low kindling point and is not very weldable, except when it is alloyed with manganese and aluminum. Magnesium is distinguished from aluminum by the use of a silver nitrate solution. The solution does not react with aluminum, but leaves a black deposit of silver on magnesium. Magnesium is produced in large quantities from sea water. It has excellent machinability, but special care must be used when machining because of its low kindling point.
Fracture test. Magnesium has a rough surface with a fine grain structure.
Spark test. No sparks are given off.
Torch test. Magnesium oxidizes rapidly when heated in open air, producing an oxide film which is insoluble in the liquid metal. A fire may result when magnesium is heated in the open atmosphere. As a safety precaution, magnesium should be melted in an atmosphere of inert gas.
Magnesium may ignite and burn when heated in the open atmosphere.