Magnesium and its alloys are being considered for structural applications in every type of vehicle because of their favorable combination of tensile strength, elastic modulus, and low density, according to ASM International, the materials information society.
In the article “Magnesium in the 21st Century,” Robert E. Brown of the Magnesium Assistance Group Inc., Prattville, Ala., describes magnesium alloys as having high strength-to-weight ratios and relatively good electrical and thermal conductivity, as well as high damping capacity.
“Magnesium is the eighth most abundant element in the Earth’s crust, and the third most plentiful element dissolved in seawater,” Brown said. “Because magnesium is found in seawater, it is available in almost limitless quantities: A cubic mile of seawater contains six million tons of magnesium metal.”
Magnesium as a structural material has been “up and down” during the 20th Century, Brown explained. “As the world supply increases and a new legion of energized researchers and scientists address the many aspects of the most abundant structural metal, magnesium will again rebound to new heights. The present trend indicates that China will be a major contributor to this development.”
Two major magnesium alloy systems are available. The first includes alloys that contain 2 to 10% aluminum, combined with minor additions of zinc and manganese. These alloys are widely available at moderate cost, and their mechanical properties are good at temperatures up to 95 to 120°C (200 to 250°F). However, above these temperatures properties deteriorate rapidly.
The second group consists of magnesium alloyed with elements such as rare earths, zinc, thorium, silver, and silicon (but not aluminum), all containing a small but effective zirconium content that imparts a fine-grain structure (and thus improved mechanical properties). These alloys generally possess better elevated-temperature properties, but they are more expensive because of their more costly elemental additions and specialized manufacturing technology.
Aluminum metal, which is not easy to get from its ores, has become a 30 million ton per year business, while magnesium has struggled to reach about 800,000 tons per year. “Realistically, world production must grow to over one million metric tons per year if it is to be seriously considered for widespread applications,” Brown said.
The largest amounts of magnesium will continue to be for aluminum alloying, but Brown expects that it will continue to be needed for desulfurization of steel “if the price is competitive.” Interest in magnesium is growing in technologies such as thixomolding, extrusions, sheet, and forgings. “Magnesium can also provide huge provide huge structural and economic advantages in automotive and aerospace applications, based on life cycle analysis,’ Brown said.
“Magnesium in the 21st Century,” a complete description of the current state of the magnesium industry and future opportunities, can be accessed and downloaded free of charge at www.asminternational.org/amp.