ASM Specialty Handbook: Magnesium and Magnesium Alloys Copyright © 1999 ASM International® M. Avedesian and H. Baker, Editors All rights reserved www.asminternational.org

Introduction: History, Production, Applications, and Markets l.j. Polmear, Department of Materials Engineering, Monash University, Victoria, Australia

MAGNESIUM is the lightest of all structural many using a modification of Bunsen's cell (Ref heating in air, after which further heating is dis­ metals. As such, it forms the basis for commer­ 3-5). In 1896, this process was jointly taken advantageous because it leads to formation of cial alloys that have found successful use in a up by Chemische-Fabrik Griesheim-Elektron undesirable oxides and oxychlorides. The Dow wide variety of applications. It is a plentiful and Aluminium und Magnesium Fabrik as the sole Chemical Company relies on flashing off the element, comprising 2.7% of the earth's crust significant producer of magnesium metal in remaining water by adding small quantities of (Ref 1). Although magnesium does not occur the world untill914-1915 (Ref6). the partially dehydrated chloride directly into in nature in the metallic form, magnesium By 1900, worldwide production had only reached a large mass of a liquid mixture of magnesium, compounds occur worldwide, and commercial approximately 10 tonnes per annum. and by 1915, sodium, and calcium chlorides contained in amounts of magnesium ores are found in most yearly production had risen to only 350 tmmes. the electrolytic cell. Norsk Hydro, the major countries. The most common ores are the car­ At that time, however, several other countries European producer, employs complete dehydra­ bonates: dolomite (MgC03·CaC03) and magne­ (notably the United States) began production, tion by heating in an atmosphere of dry hydro­ site (MgC03). The double chloride carnallite and worldwide annual output jumped to more than chloric acid (HCI). Plants in the Commonwealth (MgC12·KC1·6H20) is found to form salt depos­ 3000 tonnes by the last year of the First World its in natural brines and evaporites, such as in the War, only to fall again to 330 tonnes in 1920. Raw materials Great Salt Lake in Utah. However, the major By 1939, production was 32,000 tonnes per source of magnesium is ocean water. Magne­ annum; under the impetus of the Second World Seawater Oyster shells sium constitutes 0.13% of the world's oceans War it again increased nearly tenfold, only to fall (calcium carbonate) Natural gas (Ref 2); therefore, seawater provides a virtually again in the late 1940s. During the 1990s, pro­ inexhaustible supply of the metal. duction in the Western world has been close to 250,000 tonnes per annum, which represents ap­ c$==J proximately 90% of productive capacity. In ad­ Calcium oxide History dition, the annual estimated capacity of the (unslaked lime) Hydrochloric Commonwealth of Independent States is 50,000 acid In 1808 Sir Humphrey Davy established that tonnes, and that of The People's Republic of magnesium oxide was the oxide of a newly rec­ China is 50,000 tonnes (Ref7). ognized metal. Magnesium metal was first iso­ lated in 1828 by the French scientist Antoine­ Alexander Bussy, who fused magnesium chloride Production Processes with metallic potassium to obtain metallic mag­ ' Calcium Magnesium hydroxide chloride nesium. The first production of magnesiwn by Currently, two basic processes are used to pro­ ! solution electrolytic reduction from the chloride was ac­ duce magnesium metal; the electrolysis of fused Neutralizer complished by Michael Faraday in 1833 (Ref anhydrous magnesium chloride (MgC12) derived 3-5). from magnesite, brine, or seawater, which ac­ Magnesium chloride solution Corrnnercial production commenced in Paris counts for about 80% of the output, and thermal in the middle of the nineteenth century with the reduction of magnesium oxide (MgO) by fer­ Deville-Caron process, which uses potassium to rosilicon derived from carbonate ores. A third reduce magnesium chloride in a heated closed process has been· recently developed that uses container. For several years, the world produc­ electrolysis of fused anhydrous MgCI2 derived Sol$ide tion of magnesium metal was used almost en­ from serpentine ores. tirely in wire or powder form for photographic The electrolytic process used by many of the purposes. About 1860, Johnson Matthey & Co. producers is similar to the Dow seawater process Dry magnesium chloride in Manchester, England began British produc­ (Fig. 1), the differences residing mainly in the tion using a similar process. methods used to produce the anhydrous MgCI2 Chloride gas In 1852, Robert Bunsen, a German, construct­ (Ref 7, 8). While it is comparatively easy to ed a small laboratory cell for the electroly­ extract MgC12·6H20, complete removal of the Magnesium Ingots sis of the fused chloride (Ref 3--5). In 1886, water of crystaUization has proven to be diffi­ commercial production also commenced in Ger- cult. The first four moles can be evaporated by Fig. 1 The Dow Process 4 I Metallurgy and Alloys of Independent States have a different approach; for night aerial photography, miscellaneous fire­ lubricating oils; in the purification of argon and it involves the use of a cell feed of dehydrated works, high-energy fuels, and incendiary de­ hydrogen gases; as a "getter" in the manufacture carnallite, which is easier to reduce to the anhy­ vices. of vacuum tubes; for the production of boron, drous form (Ref7). Metallurgical Applications. In the metallur­ lithium, and calcium hydride; and for deoxygen­ Recently, a completely new process for pro­ gical field, magnesium is used in the manufac­ ating and dechlorinating boiler water. ducing the basic feedstock of anhydrous MgCI2 ture of nodular cast iron where the magnesium Electrochemical- applications of magnesium has been developed by the Australian Magne­ removes some of the sulfur and spheroidizes the and magnesium-alloy cast and wrought products sium Corporation. Gylcol is added to a MgC12 graphite to provide greatly improved ductility include cathodic protection, batteries, and photo­ solution, water is removed by distillation, and and strength. It also is used extensively to desul­ engraving. Sacrificial galvanic anodes of mag­ magnesium chloride hexammoniate is fonned furize steel. In addition, it is useful as a deoxidizer, nesium are used to extend the life of household by sparging with ammonia. Calcining then pro­ or "scavenger," in the manufacture of copper­ and industrial water heaters; underground struc­ duces a high-quality anhydrous MgC12; solvents base alloys, such as brass and bronze, and in the tures such as cables, pipelines, well casings, tanks, and ammonia can be recycled. manufacture of nickel alloys. Magnesium used and tower footings; and seawater condensers, The Magnola process (Fig. 2), an electrolytic in combination with calcium is indispensable in ship hulls, ballast tanks, and steel piling in process that uses magnesium chloride derived the Betterton-Kroll process used to remove bis­ marine environments. Magnesium has also been from serpentine ore, was developed in Canada to muth from lead. used in the construction of batteries, both dry­ take advantage of the magnesium silicate con­ By far, the largest use of magnesium is as an cell and reserve-cell types such as seawater­ tained in the tailings from asbestos mines (Ref alloying element in aluminum where it is added activated cells, and its good etching qualities 9). The tailings are leached with a strong hydro­ to improve strength and corrosion resistance. In combined with good mechanical properties and chloric acid in a novel process to produce MgClz addition, magnesium is added to zinc dieMcasting ability to withstand wear have contributed to its solution, which is purified by pH adjustment and alloys to improve mechanical properties and di­ use as photoengraving plate. ion exchange techniques to generate a concen­ mensional stability. Magnesium is also a con­ Structural Applications. Due to its many at­ trated ultra-high-purity brine for dehydration stituent in other zinc products, such as roofmg tractive properties, magnesium has been suc­ and electrolysis. sheet, photoengraving plate, the sheet used in cessfully used in various structural applications. The thermic-reaction processes are batch op­ dry-cell batteries, and galvanizing baths. Nickel, Its extreme lightness alone makes it attractive in erations carried out under a vacuum and gener­ nickel-copper, and copper-nickel-zinc alloys also all parts that are moved or lifted during their ally use dolomite as the ore and ferrosilicon as benefit from the use of magnesium additives. manufacture or use. Low inertia, which results the reductant. Volatile magnesium is produced, Chemical Applications. In the chemical from the low density of magnesium, is especially which distills off and is collected in a container. field, magnesium is used in the well-known The oldest of these thermic-reaction processes Grignard process for the production of complex was developed in 1941 by the Canadian scien­ and specialized organic and organometallic Raw materials tist Lloyd Montgomery Pidgeon. The Pidgeon compounds. It is also used in the production of Volomlte ore Slllca ore Coke + process (Ref 8) uses externally heated retorts magnesium alkyls and aryls; as a neutralizer in (magnesium carbonate + (quartizite) scrap iron of relatively small diameter, each producing calcium carbonate) about 120 kg (265 !b) of magnesium per day (Fig. 3). Plants are located in Canada, China, Raw materials and India. Natural gas ll~i-11 Asbestos tailings c$=J The Magn6thenn process (Fig. 4) of France's (serpentine, magnesium Calcined dolomite Pechiney Electrometallurgie, which was devel­ silicate) (magnesium oxide + Ferro-silicon oped shortly after the Second World War, differs calcium ox!de) from the Pidgeon process in that it produces a molten slag that can be tapped off without t breaking the vacuum (Ref 8, 10). The furnace is Magnesium electrically heated internally, and alumina is chloride brine Calcined used as a flux to reduce the melting point of the Hydrochloric dolomite powder Ferro-silicon slag. Batch sizes can run as high as II ,000 kg acid powder (24,000 !b). Planlll are located in France, the I United States, and the former Yugoslavia. I· Purified brine Calcined+· dolomite + ferrosilicon powder Applications Hydrochloric acid Magnesium has been used for a wide variety synthesizer of applications, including pyrotechnics and met­ allurgical, chemical, electrochemical, and struc­ Calcined dolomite - tural applications. Although the main focus of ferrosi!icon pellets this Handbook is the use of magnesium and mag­ nesium alloys to produce cast and wrought prod­ ucts for structural applications, the nonstructural 1 Chlorine uses of the metal are important in many industries. Anhydrous Pyrotechnics. Because finely divided powder magnesium chloride Magnesium crystals of magnesium-aluminum alloy containing up­ wards of 30% AI burns with a brilliant white light, the first industrial use of magnesium was in pyrotechnics. (Because this light is even ~ore suited for photographic film than natural light, Magnesium ingots Magnesium ingots it was used for flashlights for photography.) Mag­ nesium powder also has been used for flares Fig. 2 The Magnola process Fig. 3 The Pidgeon process Introduction: History, Production, Applications, and Markets I 5 advantageous in rapidly moving parts. In addi­ Consumption and Markets sources, suggests that consumption of magne­ tion, the low density of magnesium allows sium per vehicle could increase 40 fold during thicker sections to be used in parts, eliminating Consumption of magnesium in the Western the current decade (Ref 11). On the other hand, a the need for a large amount of stiffening, simpli­ world in 1997 is summarized in Fig. 5, which more mOOest prediction relating to the use of fying the part and its manufacture. While light shows that almost half of the 333,700 tonnes magnesiwn die castings in cars and trucks indi­ weight is probably the most important factor in was used as an alloying element in alwninum, cates an increase in consumption in the Western the selection of magnesium in most structural and a further 18% was added to ferrous alloys to world from 24,000 tonnes in 1992 to between applications, otherproperties are also significant desulfurize steel or to prOOuce nOOular cast iron. 92,000 and 142,000 tonnes in 2002 (Ref 12). for different uses. Other important factors in­ Of the remainder, only some 101,000 tonnes, or This represents a change from 0.6 kg (1.3 !b) to cludeelevated-temperaturepropertiesinaircraft 30% of the total, were actually used to produce between 2.5 and 3.5 kg (between 5.5 and 7.71b) and missiles (compared to plastics and polymer­ structural magllesium alloys, with die castings per vehicle. matrix composites), fatigue strength in wheels, (95,300 tonnes) being the primary product. Trends in magnesium alloys for the automo­ damping in electronic housings for aircraft and In the aeronautical market, air-frame appli­ tive market were analyzed more recently by missiles, dimensional stability in electronic cations for magnesium in new designs have Magers (Ref 13). He estimates that the market housing an din jigs and :fixtures, machinability in virtually disappeared, and the most significant for magnesium die castings will grow from the tooJing plate, dent resistance in luggage, non use of magnesium alloys has been cast engine 51,000 tonnes of parts produced in 1996 to marking qualities in textile machinery, alkaline and transmission housings, notably for heli­ slightly more than 100,000 tonnes in 2000 and resistance in the concrete industry, and low re­ copters. will reach close to 200,000 tonnes by 2006. Ap­ sistance to the passage of x-rays and thermal Historically, the Volkswagen Beetle automo­ proximately 80% of this market is expected to neutrons in x-ray cassettes and nuclear fuel cans. bile has represented the largest single applica­ go towards die casting automotive parts. This Historically, magnesium has been used to tion of magnesium alloys, which were used for growth will be led by the market in North Amer­ make military equipment, such as shelter frames, the crankcase and transmission-housing cast­ ica, followed by Europe, South America, and the mortar bases, and missiles. It has been used in ings. These castings weighed a total of 17 kg Pacific Rim, in that order. Growth to the year aircraft and surface-vehicle frames, panels, (37.5 lb), which was said to represent a savings 2000 will see a continuation of the types of parts of 50 kg (110 1b) when compared with using cast floors, brackets, and wheels, as well as in engine that have been developed in magnesium over the iron. This saving of weight was critical for the components, such as pistons and housings. In­ last 10 to 15 years. stability of the rear-engined vehicle. More than dustrial machinery, such as textile warp beams The importance of magnesium die castings in and electric-motor end bells, use magnesium, as 20 million units were produced since the Bee­ the automotive market is emphasized by the re- do pieces of goOOs-handling equipment, such as tle was first introduced in the 1930s, repre­ dock boards and bulk shipping containers. Plas­ senting a consumption of more than 400,000 terers' tools and other manually handled tools tonnes of magnesium. Chemical ~- W''""'"h' products use magnesium, as do computer cases and other Currently, the average amount of magnesium 2% 1% office machines. Magnesium is also used in used in the production of automobiles is 3 kg Electrochemical Metal household items, such as sewing machines, and (6.6 !b). Future estimates vary widely. For ex­ 2.5% ---~ reduction 1.5% sporting goOOs, such as archery bow handles. ample, Table 1, which is quoted from Japanese Nodular cast iron

Raw materials I~-- Other 2% Dolomite ore Alumina Ferro-silicon (magnesium carbonate +calcium carbonate)

Pulverized Calcined Alumina-dolomite dolomite dolomite'* blend Fig. 5 Consumption of magnesium in Western world in 1997 (total 333,700tonnes). Amount used for Pelletized magnesium alloys is shown shaded. Courtesy of Interna­ blend tional Magnesium Association

Calcined dolomite Crushed ferro­ c$=J silicon Table 1 1993 forecast of major materials Calcined blend usage in the average motor car ~ Retort furnace 1989 1995 2000 1989to2000 Material actual, kg forecast, kg forecast, kg change,% L------+-Calcium silicate +iron Steel 900 600 200 -77 Magnesium crystals Aluminum 55 130 270 +390 Plastics 115 170 220 ~100 Glass 30 15 0 +3900 Magnesium I 5 40 -40 Other 200 180 120 Total 1300 1100 850 Magnesium ingots Source: Ref 12 Fig. 4 The Magnetherm process 6 I Metallurgy and Alloys cent trend set by major automobile producers in dead weight of a motor vehicle corresponds to five AM20 and AM50 magnesium alloy die who align themselves with magnesium produc­ an increase in fuel economy of 5.5%. This, in castings and weighs 8.4 kg (18.5 lb). It is ers. Volkswagen has invested in the Israel pro­ tum, means reduced exhaust emissions. This is claimed that a comparable steel seat design ject to produce magnesium from Dead Sea the purpose ofthe United States government's would weigh an estimated 35 kg (77 lb) and brine; Ford has invested in the pilot produc­ "Corporate Average Fuel Economy" (CAFE) require between 20 and 30 stampings and weld­ tion plant in Queensland, Australia; the Aisin legislation, which requires manufacturers to ments (Ref 15, 16). Figure 7 shows the assembly (Toyota) group has invested in the new No­ achieve progressive improvements in the fuel of a Ford steering column, which is composed of randa project in Canada; and General Motors economies of vehicles they produce. This leg­ three magnesium alloy die castings and weighs has signed a long-term supply contract with islation is providing much of the stimulus to 1.2 kg (2.61b). Magnesium castings in the Volvo Norsk Hydro. weight-reduction programs through material LCP 2000 concept motor car have a total fin­ The future of magnesium will be controlled substitutions. Table 2 presents a selection of ished weight of 50 kg (110 !b) (Ref 17). by metal prices and the role of government magnesium alloy components being used in Another major area in which the structural use legislation, particularly in the United States various new production vehicles, two exam­ of magnesium is expanding is the use of magne­ and Japan. Regarding such legislation, it has ples of which are shown in Fig. 6 and 7. Fig­ sium die castings for such applications as com­ been estimated (Ref 14) that each 10% saving ure 6 shows the seat frame for a Mercedes­ puter housings and mobile-telephone cases Benz roadster, which has been produced from where lightness, ability to be thin-wall cast, and provision of electromagnetic shielding are spe­ cial advantages.

REFERENCES

I. R.J.L. Stanner,Am. Sci., Vol64, 1976, p 258 2. C.M. Shigley, J. Met .• Vol3, 1951. p25 3. W.H. Gross, The Story of Magnesium, Ameri­ can Society for Metals, 1959. p 17 4. C.J. Ball, 1./nst. Met., Vol84, 1955-56, p 399 5. N. Hoy-Petersen. Proc. 47th Annual World Magnesium Conf, VoltS, futemational Mag­ nesium Association, 1990, p 18 6. E.V. Pannell, Magnesium, Its Production and Us~ Pitman Publishing Carp., 1944. p 25 7. B.B. Clow, Proc. Im. Conf on Magnesium Al­ Fig.6 Die-cast magnesium alloy seat frame for Mer­ Fig. 7 Ford motor car steering column assembly composed loys and Their Applications, Deutsche Gesell­ cedes Benz motorcar of three magnesium die castings. Source: Ref 16 schaft fiir Materialkunde E.V .• 1992, p 13 8. L.M. Pidgeon, Encyclopedia of Materials Sci­ ence & Engineering, Vol 4, Pergamon Press, 1986 9. C. Celik, N.E. Ghatas. J. Lenz, C. Letourneau, Table 2 Selection of magnesium alloy components in new production motor cars and trucks and R. Santiago, Proc. Int. Symp. on Advances in Production and Fabrication of Light Metals and Metal Matrix Composites, Metallurgical Company Model Alloy Society, Canadian Institute of Mining and Met­ Foro Clutch housing, oil pan, steering cohunn Ranger AZ91HP allurgy. 1992, p 3 AZ91B 10. E.F. Emley, Principles ofMagnesium Technol­ Four-wheel-drive transfer case housing Aerostar 1994 AZ91D ogy, Pergamon Press, 1966. p 59 Manual tmnsmission case housing Bronco AZ91D General Motors Valve cover, air cleaner, clutch housing Corvette AZ91HP II. R.L. Koenig and G.L. Dunlop, Mater. Aus­ (manual) tra/as .• Vol24, 1992, p 12 Inductioncover NorthStarV-81992 AZ91D 12. D.J. Lewis, Magnesium: Opportunities for Aus­ Clutch pedal, broke pedal, steering cohunn "W" Oldsmobile, AZ91D tralian Industry, Department of Industry, Tech­ brackets Pontiac, Buick Chrysler Drive bmckets, oil pan Jeep 1993 nology & Regional Development, Steering column bmckets LH midsize 1993 Commonwealth of Australia, 1993 Drive bmckets, oil pan Viper 13. D. Magers, International Outlook, Magnesium Daimler-Benz Seat fmmes 500 SL AM20/SO in Automotive, IMA Automotive Seminar, Alfa-Romeo Miscellaneous components (45 kg, or99 GTV AZ91B Im) 1997 PorscheAG Miscellaneous components (53 kg, or 120 911 14. R. Brown, Light Meta/Age, Vol 50 (No.5 and lffi) 6), 1992, p 21 Wheels (7 .44 kg, or 16.4 \bs, each) 944Turbo AZ91D 15. T.J. Ruden, Int. Symp. on Production, Refining Honda Cylinder head cover City Turbo AZ91D and Fabrication of Light Metals, Metallurgical Wheel<; (5.9kg, or 130lbs, each) Prelude AM60B Toyota Steering wheel Lexus AM60B Society, Canadian Institute of Mining and Met­ Fueling engineering Cylinder block, oil sump, camshaft SHQ AZ91E allurgy, 1990 cover,front cover assembly Quad4 ZE41A 16. D.L. Albright, T.J. Ruden, and J. Davis, Light Aerotech ZC63 Metal Age, Vol 50 (No. 1 and 2). 1992. p 31 17. A. Wickberg and R. Ericsson, SAE Tech. Paper Source: Ref 12 Ser., No. 850418.1985