IT'S ELEMENTAL!
MAGNESIUM GERALD D. COLE, LIGHTWEIGHTSTRATEGIES
M
Magnesium's first uses in flares, tracer bullets, incendiary bombs, fireworks, and flash photography were based on its significant chemical reactivity In fact, most of us learned about magnesium from our high school teachers as we watched a lit ribbon produce a bright flare. And it is this fiery perception that remains to this day It was only in the late 1990s that magnesium was reclassified from a reactive to an engineering metal by the Minerals, Metals & Materials Society, the dominant North American metals society A quick search on Google reveals over 1.5 million citations for "magnesium." More than 1.4 million are connected to nutritional and medicinal uses, since it is an important element in both plant and animal life. Magnesium has valuable chemical uses: in reducing uranium and titanium from their ores, in eliminating sulfur from steel, and in F L Y I N G H I G H A Convair B-36A nuclear bomber. producing high-strength (spheroidal graphite) cast iron. MagThe plane contains about 10,000 kg of Mg. nesium oxides are also central to al, with a density that is about the same as high-temperature refractories. Up until recently magnesium's main use was as a 1-3% engineered plastics, two-thirds the density of aluminum, and one-quarter that of steel. alloy in the 20 million tons of aluminum alIt is a little weaker (except in fatigue) and a loy produced annually bit softer than aluminum; conventional alloys The recent history of magnesium is creep at temperatures above 125 °C, but new- marked by two events. First, 70,000 World er alloys almost equal aluminum. War II Messerschmitt and StuMost properties are significandy ka dive bombers contained magbetter than engineered polymers. nesium fuselages, engine parts, Magnesium's main limitations are and wheels. (U.S. Convair B-36 its low formability at room tembombers contained 10,000 kg.) perature, but this is much imThere is no magnesium in today's proved at temperatures greater aircraft, but there is in some jet than 200 °C. Molten magnesium engine parts, rockets, missiles, alloys have outstanding fluidity THIS ELEMENT and helicopter rotor housings BROUGHT and can be cast into very large (machined from high-temperaTO YOU BY (1 m X 2 m), ultrathin (1-2 mm), ture alloy castings). Second, the CAMBREX high-surface-detail shapes. 1939-2003 Volkswagen Beetle It was the influence of war showed the world that magnethat changed magnesium's stature from a sium has significant automotive applicacuriosity to an industrial material. And it tions, with almost 25 kg ofmagnesium castwas in Germany where the body of knowlings in its transmission housing and edge originated on how easily magnesium air-cooled engine. could be alloyed (with aluminum, zinc, and Five years ago, magnesium's cost was manganese) and formed (cast, forged, extwice that of aluminum (about $4.00 per truded, welded, and machined). In fact, kg). This was based on 4 0 , 0 0 0 - 6 0 , 0 0 0 magnesium was referred to as "the Gerton expensive, continuous, chemical plants man metal" well into the 20th century that reduced the combined magnesium in AGNESIUM IS T H E E I G H T H
most common element and the sixth most abundant metal, making up about 2.5% of Earth's surface; seawater contains 0.14% magnesium. The element is concentrated in the minerals carnallite (MgCr»6H 2 0), magnesite (MgCO^, and dolomite (MgCCyCaCO^. Magnesium is the lightest industrial met-
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MAGNESIUM AT A GLANCE Name: From the Greek Magnesia, a city in Thessaly. Atomic mass: 25.31. History: Recognized as an element by Joseph Black in 1755 and isolated in 1808 by Sir Humphry Davy. Occurrence: Isolated from seawater, carnallite, magnesite, and dolomite. Appearance: Silvery white, solid metal Behavior: Ignites at temperatures near 500 °C. Lustrous, soft, and malleable. Uses: Essential component of many enzymes and chlorophyll. It is used as a bulk metal, in lightweight alloys, and as a "sacrificial" electrode. ,
magnesite, carnallite, and seawater to MgCl 2 ; smelters (with their expensive electricity) reduced the chloride to metal. Using thousands of small, low-cost, coal-fired kilns, Chinese producers now directly reduce dolomite in low-vacuum steel tubes and condense magnesium "crowns" in 60kg batches at one-fortieth the cost per ton of capacity compared with Western producers. From nothing six years ago, China now produces one-half the world's supply and has forced magnesium prices down to nearly those of aluminum ($1.60 per kg). Magnesium production is one-fortieth that of aluminum, but it is growing five times faster, at 5-10% annually as its valuable properties are increasingly exploited to reduce weight, increase fuel efficiency and reduce emissions. The automotive industry is the largest user. Light, rugged, "handheld everything" that requires electronic shielding can be made from ultra-thin (about 1 mm) high-pressure die castings, injection-molded semisolids (Thixomolding), and stamped sheets. Tens of millions of laptop computers, PDAs, cellphones, camera bodies, and projection equipment are produced annually this way There is a growing use for magnesium in power tools; kitchen appliances; and lawn, garden, and sporting equipment where magnesium's excellent vibration absorption adds consumer value. Unlike most polymeric materials, magnesium alloys have outstanding impact and dent resistance—and they are 100% recyclable. As prices decrease, new alloys will be invented and new uses found to make magnesium the wonder metal ofthe 21st century Gerald D. Cole is the principal in LightWeightStrategiesLLC. He was a FordMotor Co. global lightweighting expert for 35years until his retirement in 2001. HTTP://WWW.CEN-ONL-|NE.O.'RG.'-
