IN the 21St CENTURY Magnesium Will Become the Material of Be a Major Contributor to This Development

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The Convair RB-36D Peacemaker was the jet-augmented version of the U.S. Air Force’s intercontinental strategic bomber. It was the world’s largest bomber, and contained 19,000 pounds of magnesium. Service experience in all environments proved that magnesium could satisfy all the requirements of a structural material. Four General Electric J-47 jet engines, mounted in pairs under the outer wing edges, supplement six Pratt & Whitney piston engines. (U.S. Air Force photo) MAGNESIUM IN THE 21st CENTURY Magnesium will become the material of be a major contributor to this development. Two major magnesium alloy systems are avail- choice as designers strive to improve able. The first includes alloys that contain 2 to 10% energy efficiency in transportation. aluminum, combined with minor additions of zinc and manganese. These alloys are widely available at moderate cost, and their mechanical properties are Robert E. Brown* good at temperatures up to 95 to 120°C (200 to Magnesium Assistance Group Inc. 250°F). However, above these temperatures prop- Prattville, Alabama erties deteriorate rapidly. The second group consists of magnesium al- agnesium and its alloys are being con- loyed with elements such as rare earths, zinc, tho- sidered for structural applications in rium, silver, and silicon (but not aluminum), all every type of vehicle because of their containing a small but effective zirconium content favorable combination of tensile that imparts a fine-grain structure (and thus im- Mstrength, elastic modulus, and low density. Magne- proved mechanical properties). These alloys gener- sium alloys have high strength-to-weight ratios and ally possess better elevated-temperature proper- relatively good electrical and thermal conductivity, ties, but they are more expensive because of their as well as high damping capacity. Magnesium is more costly elemental additions and specialized the eighth most abundant element in the Earth’s manufacturing technology. crust, and the third most plentiful element dissolved Aluminum metal, which is not easy to get from in seawater. Because magnesium is found in sea- its ores, has become a 30 million ton per year busi- water, it is available in almost limitless quantities: ness, while magnesium has struggled to reach about A cubic mile of seawater contains six million tons 800,000 tons per year. Realistically, world produc- of magnesium metal. tion must grow to over one million metric tons per Magnesium as a structural material has been up year if it is to be seriously considered for widespread and down during the 20th Century. As the world applications. This article discusses the magnesium supply increases and a new legion of energized industry today and what may happen in the future. researchers and scientists address the many aspects of the most abundant structural metal, Magnesium development magnesium will again rebound to new heights. It has been 200 years since the great Cornish in- The present trend indicates that China will ventor, Sir Humphrey Davy, developed methods *Member of ASM International to isolate aluminum, sodium, calcium, barium, ADVANCED MATERIALS & PROCESSES/JANUARY 2009 31 Magnesium.qxp 12/17/2008 11:30 AM Page 2

strontium, and magnesium. Sir Humphrey first iso- grew to forgings, extrusions, and rolled products, lated aluminum in 1807 and identified magnesium mostly in Germany. However, magnesium ap- in 1808. He also recognized the anesthetic proper- plications did not expand rapidly in the United ties of nitrous oxide (laughing gas), and invented States until the military buildup of World War II. a safety lamp for miners. Perhaps his most impor- Postwar development was more ambitious than tant contribution was his discovery of Michael successful. However, the industry persevered, Faraday. and magnesium applications and consumption Michael Faraday produced magnesium metal have been growing slowly but steadily over the by the electrolysis of fused anhydrous magnesium past 50 years. chloride in 1833. Commercial production of magnesium by electrolysis is credited to German sci- Magnesium production entist Robert Bunsen, who made magnesium in a Magnesium production grew slowly over the laboratory cell in 1852. In the electrolytic cell, mag- period from 1950 to 1990. At this point, China be- nesium chloride is decomposed by an electric cur- came very involved in building small magnesium rent into molten magnesium and chlorine gas. The production plants that were based on the Pidgeon magnesium metal is drawn off and cast into pri- Process of thermal reduction of calcined dolomite mary ingots for remelting. The chlorine is collected by ferrosilicon. In this process, calcined dolomite, and recycled in gaseous form. ferrosilicon, and fluorspar are finely ground in a After a long slow introduction, magnesium ball mill and then briquetted dry into almond size structural applications began as castings and pieces that are charged into horizontal alloy steel ten-inch retorts. The retorts are placed under vacuum and the released magnesium vapor is condensed in a steel condenser located in the water-cooled end of the retort outside the furnace. The solid condensate is melted, refined, and cast into ingots. Many provinces in China have large quantities of dolomite, and in a remarkable demonstration of both free enterprise and indus- trial cooperation, magnesium production soared. The rapid increase in supply drove the world price down, and eventually the older magnesium plants based on the electrolytic process started closing, as they could no longer remain profitable at the new price levels. In 1999, Dow Chemical closed its plant in Freeport, Texas. The plant produced magnesium by an electrolytic process with sea water as feed- stock, but could no longer compete. Dow had been producing magnesium for over 80 years. The electrolytic magnesium production plants operated by Norsk Hydro at Becancour, Quebec, and the Timminco Plant in Haley, Ontario, were This pie chart shows the consumption of magnesium by application. both closed in 2007. For the first time since 1941, no primary magnesium was produced in Canada. The major European producers in France and Norway closed their electrolytic plants as Chinese imports drove prices down. There was a brief at- tempt to put anti dumping penalties on the magnesium coming into Europe, but they were not effective. The United States has imposed heavy anti dumping penalties on imports of magnesium from China, protecting the sole remaining primary magnesium production plant in North America, US Magnesium LLC, Salt Lake City, Utah. US Mag uses the brines from the Great Salt Lake as the source of magnesium. Its electrolytic plant has been very successful and was recently upgraded to 52,000 metric tons per year of capacity. At this time, the plant is operating at full capacity.

Magnesium growth Magnesium production will reach the million This is the 1970s BMW Rennsport motorcyle. It contained a magnesium engine ton per year mark in a few years, if it just con- and magnesium gearbox castings. tinues to grow at the same pace that it has for 32 ADVANCED MATERIALS & PROCESSES/JANUARY 2009 Magnesium.qxp 12/17/2008 11:30 AM Page 3

many years. The recent drive to reduce energy consumption in transportation may help increase the Summary of magnesium future rate of growth. • Production reached about 789,000 tons in 2007. Production of magnesium sheet and extrusions was developed and expanded during WWII. The • Production has been increasing about 10% per year for the past B-36 bomber included very large quantities of mag- ten years. nesium sheet, and the smaller Northrop XP-56 also • The largest amounts of magnesium will continue to be for was a magnesium intensive aircraft. Northrop de- aluminum alloying. veloped a shielded arc welding process for the XP- • It will continue to be needed for desulfurization of steel, but the 56 construction program. They named it Heliarc, price must be competitive. because helium gas acted as the shielding. Magnesium parts were developed by Chrysler • Interest is growing in technologies such as thixomolding, during the 1950’s, but the programs were short extrusions, sheet, and forgings. lived. Recently Chrysler built an all-magnesium • Automotive applications by U.S. automakers have declined from car, but at last check, had no plans for large 75,000 mt per year in 2000 to an estimated 34,000 mt in 2008. At quantities of magnesium in regularly produced present, China is showing the fastest development in this area. automobiles. • Magnesium can provide huge structural and economic Magnesium predictions advantages in automotive and aerospace applications based on This predicted development of magnesium was life cycle analysis. made in early 2008. Needless to say, there have • Demand must grow to push production. been amazing economic changes in the world over • Demand can be pushed by higher production. the past few months, and these will surely impact the timetable of magnesium growth. At the moment, much development depends on the U.S. automakers should also create more oppor- the expansion of magnesium applications in the tunities for the number of magnesium applications auto industry world wide. The Chinese are leading to grow. the efforts at the present time. They produce the most magnesium and are quickly learning to use For more information: Robert E. Brown is president of it in their domestic operations. the Magnesium Assistance Group Inc., 226 Deer Trace, The recent uptick in gas prices and downfall of Prattville, AL 36067; tel: 334/365-9184; [email protected].

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