Magnesium, the worlds lightest structural metal, is a silvery-white material weighing only two-thirds as much as aluminum. Magnesium does not possess sufficient strength in its pure state for structural uses; but when it is alloyed with zinc, aluminum, and manganese, it produces an alloy having the highest strength/weight ratio.

Magnesium is probably more widely distributed in nature than any other metal. It can be obtained from such ores as dolomite and magnesite, from underground brines, from waste liquors of potash, and from seawater, With about 10 million pounds of magnesium in 1 cubic mile of seawater, there is no danger of a dwindling Supply.

Magnesium is used extensively in the manufacture of helicopters. Its low resistance to corrosion has been a factor in reducing its use in conventional aircraft. The machining characteristics of magnesium alloys are excellent. Usually the maximum speeds of machine tools can be used with heavy cuts and high feed rates. Power requirements for magnesium alloys are about one-sixth of those for mild steel. An excellent surface finish can be produced, and, in most cases, grinding is not essential. Standard machine operations can be performed to tolerances of a few ten-thousandths of an inch. There is no tendency of the metal to tear or drag. Magnesium alloy sheets can be worked in much the same manner as other sheet metal with one exception-the metal must be worked while hot. The structure of magnesium is such that the alloys work harden rapidly at room temperatures. The work is usually done at temperatures ranging from 450F to 650F, which is a disadvantage However, compensations are offered by the fact that in the ranges used, magnesium is more easily formed than other materials. Sheets can be sheared in much the same way as other metals, except that a rough flaky fracture is produced on sheets thicker than about 0.064 inch. A better edge will result on a sheet over 0.064 inch thick if it is sheared hot.

Annealed sheet can be heated to 600F, but hard-rolled sheet should not be heated above 275F. A straight bend with a short radius can be made by the Guerin process, as shown in figure 1-24, or by press or leaf brakes. The Guerin process is the most widely used method for forming and shallow drawing, employing a rubber pad as the female die, which bends the work to the sharpe of the male die.

Magnesium alloys possess good casting characteristics. Their properties compare favorably with those of cast aluminum. In forging, hydraulic presses are ordinarily used; although, under certain conditions, forging can be accomplished in mechanical presses or with drop hammers.

Magnesium embodies fire hazards of an unpredictable nature. When in large sections, its high thermal conductivity makes it difficult to ignite and prevents its burning. It will not burn until the melting point is reached, which is approximately 1,200F, However, magnesium dust and fine chips are ignited

easily; precautions must be taken to avoid this if possible. If they are ignited, you should extinguish them immediate y with an extinguishing powder such as powdered soapstone, clean, dry, unrusted cast iron chips, or graphite powder.

Water or any standard liquid or foam extinguisher causes magnesium to burn more rapidly and may cause small explosions.