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
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.