Density magnesium alloys

Lithium magnesium alloys, developed during World War 11, have found uses in aerospace appHcations. Lithium alters the crystallization of the host magnesium from the normal hexagonal stmcture to the body-centered cubic stmcture, with resultant significant decreases in density and increases in ductibiHty. 

Because of iheir low density these alloys are attractive for use v.-herc weight is at a premium. The majoi drawback to the use of these alloys is their ability to ignite in air (this can be a problem in machining) they are also costly. Magnesium alloj-s are used in both the wrought and Hie-casi forms, the latter being the most frequently used form. 

Strength and low density are important properties in the manufacture of airplanes, automobiles, metal luggage, ladders, shovels and other gardening equipment, racing bikes, skis, race cars, cameras, and power tools. A typical magnesium alloy contains about 90 percent magnesium, 2 to 9 percent aluminum, and small amounts of zinc and manganese. 

The primary benefit of magnesium in structural applications is its low density which is two-thirds that of aluminum. However, the use of magnesium alloys in the automotive sector continues to be restricted for more arduous applications where improved designs have increased component temperatures. Creep is considered a most important factor at working temperatures at or more than 423 K. 

Magnesium is thermodynamically one of the less noble metals, and it can protect most other metals when used as sacrificial anodes (see Section 10.4). In the atmosphere the metal is covered by an oxide film. Therefore it resists rural atmospheres but is subject to pitting in marine atmospheres. Magnesium alloys are also liable to SCC and erosion corrosion, and are attacked by most acids. Mg alloys are used in automobile engines, aircraft, missiles and various movable and portable equipment, in all cases primarily because of their low density (1.76 g/cm ). 

Magnesium has the lowest density (1.7g/cm ) of all structural metals, having about one-fourth the density of iron and one-third that of aluminum. This very low density makes magnesium and magnesium alloys useful wherever low weight is important, if not required. 

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