Magnesium and Magnesium Alloys

treatment-the tensile strength rising from 70,000 psi in the annealed state to 200,000 psi in the heat-treated state. The resistance of beryllium copper to fatigue and wear makes it suitable for diaphragms, precision bearings and bushings, ball cages, spring washers, and nonsparking tools. Monel Monel, the leading high-nickel alloy, combines the properties of high strength and excellent corrosion resistance. This metal consists of 67 percent nickel, 30 percent copper, 1.4 percent iron, 1 percent manganese, and 0.15 percent carbon. It cannot be hardened by heat treatment; it responds only to cold-working. Monel, adaptable to castings and hot- or cold- working, can be successfully welded and has working properties similar to those of steel. It has a tensile strength of 65,000 psi that, by means of cold-working, may be increased to 160,000 psi, thus entitling this metal to classification among the tough alloys. Monel has been successfully used for gears and chains, for operating retractable landing gears, and for structural parts subject to corrosion. In aircraft, Monel has long been used for parts demanding both strength and high resistance to corrosion, such as exhaust manifolds and carburetor needle valves and sleeves. K-Monel K-Monel is a nonferrous alloy containing mainly nickel, copper, and aluminum. It is produced by adding a small amount of aluminum to the Monel formula. It is corrosion resistant and capable of hardening by heat treatment. K-Monel has been successfully used for gears, chains, and structural members in aircraft that are subjected to corrosive attacks. This alloy is nonmagnetic at all temperatures. K-Monel can be successfully welded. Magnesium and Magnesium Alloys Magnesium, the world’s 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 450°F to 650°F, which is a disadvantage However, com-pensations 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 600°F, but hard-rolled sheet should not be heated above 275°F. 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 1,200°F, However, magnesium dust and fine chips are ignited 1-34