Lower Cost Key to Magnesium’s Lightweighting Uses

For automakers, “lighten up” is not mood-altering advice but an imperative to shave hundreds of pounds of mass from cars and trucks to meet rising fuel-economy standards that kick in during the next decade.

One of the most promising materials for achieving weight reduction is magnesium. But because of its high cost and energy consumption in the manufacturing process, the metal is uncompetitive for most applications.

Government and industry now are partnering to boost magnesium use in lowering vehicle weight in coming years. The Advance Research Products Agency-Energy recently awarded $32 million in grants to develop processes for cost-effective and energy-efficient manufacturing of lightweight metals for vehicles.

Research will focus on less-expensive and more energy-efficient ways of producing magnesium for vehicles designed to meet increasingly stringent emissions and fuel-economy regulations. ARPA-E, part of the U.S. Department of Energy, also is funding better ways to make aluminum and titanium for vehicles.

Magnesium currently is sparingly used in vehicles because it is about seven times more expensive to make than steel. Its price ranges from about $2.90 to $3.50 per pound – about 75% more than steel and 33% more than aluminum.

Part of that is due to stiff tariffs levied on imported magnesium. One-third of the metal is imported from China, which has the world's largest reserves and is the biggest global producer of magnesium. Chinese producers use the Pidgeon process that depends on a lot of inefficient coal-fired energy – creating massive amounts of carbon-dioxide emissions.

The U.S. has only one bulk magnesium plant in Utah that uses electrolysis to extract magnesium from molten salt brine in the Great Salt Lake.

Three of the ARPA-E grants encourage cleaner and cheaper magnesium production. A $2.43 million grant to the Pacific Northwest National Laboratory funds research into an organic process of extracting magnesium salt from seawater, which normally has low concentrations of the metal, making extraction difficult, energy-intensive and expensive.

“Reinventing the magnesium production process so it's more affordable can help grow the magnesium market and decrease U.S. reliance on foreign-made materials,” says Pete McGrail, a PNNL laboratory fellow. “We expect our method will be 50% more energy-efficient than the U.S. current magnesium production process.”

McGrail tells WardsAuto in an email that PNNL's process breaks magnesium down to an “organo-magnesium compound.” He says this produces magnesium flakes that are hot-pressed into ingots. “So, we actually take maximum advantage of magnesium’s ductility in the process,” he says.

The PNNL process requires temperatures no greater than 572° F (300° C), one-third the level required by the conventional U.S. process.

Global Seawater Extraction Technologies and the owner of the Utah plant are partnering with PNNL in the research.

Another approach funded by ARPA-E employs solar power to produce magnesium and synthesis gas, or syngas. The 3-year, $3.6 million grant to University of Colorado-Boulder professor Alan Weimer seeks to create magnesium with a cooling process that produces a gas-to-solid metal phase change inside a reactor.

Magnesium production today uses electricity 24 hours a day, a method whose high energy consumption during daylight hours makes it particularly expensive. “Our plan is to use solar energy to power our reactor in the daytime and use electricity (from the grid) only at night during off-peak hours,” Weimer says.

The Colorado process involves the reaction of carbon and magnesium oxide, which are heated to high temperatures in a hybrid solar-electrical reactor to produce magnesium vapor and carbon-monoxide gas. The magnesium vapor is converted into a solid metal. The carbon monoxide is combined with hydrogen produced by using excess heat recovered from the reactor to split water into its component parts of hydrogen and oxygen, resulting in the production of syngas that can be made into diesel fuel or gasoline.

“We anticipate that the demand for magnesium will increase as industry looks to produce lower- weight, higher-mileage vehicles,” Weimer says.

Another ARPA-E grant to Valparaiso University in Indiana also seeks to produce magnesium with solar-thermal energy. The 3-year, $2.3 million project could result in lower carbon emissions and less electricity use.

Magnesium is 75% lighter than steel and 33% lighter than aluminum. By 2020, magnesium parts will contribute to a 15% weight reduction in cars and trucks, leading to fuel savings of 9% to 12%, according to the U.S. Automotive Materials Partnership comprising Chrysler, Ford and General Motors.

The partnership says automakers used only 10 lbs. (4.5 kg) of magnesium per vehicle in 2005. That has grown slightly since then, but is still severely limited because of cost.

The industry target is to use an average of 350 lbs. (159 kg) of magnesium components in vehicles by 2020. This would significantly lower the weight of the average car from the current 3,360 lbs. (1,524 kg).

Such weight reduction would result in better performance and less noise, vibration and harshness, mainly by replacing multipart components with large castings. A magnesium third-row seat frame, for instance, could weigh 40 lbs. (18 kg) less than steel.

Ford uses one of the industry’s largest die-cast magnesium structures in the liftgate of the Lincoln MKT. The metal also is used in Ford Explorer seats.

Matthew Zaluzec, global materials and manufacturing manager for Ford, predicts that beyond 2020, magnesium holds the potential for reducing vehicle weight 20%. But he says one of the big concerns about the metal is that it lacks ductility for energy absorption and shears easily.

Ford has done some developmental work on magnesium sheet meant to overcome this characteristic. “If I could get (magnesium sheet) wide enough, I would use it for fenders and roofs,” Zaluzek says. “But I wouldn't use it for a crash rail or a bumper beam.” His goal is to modify magnesium's chemistry to improve its ductility.

Zaluzec says magnesium could compete with aluminum in non-crash critical applications. “If we can crack the chemistry to make magnesium more ductile, it could be used in front and rear shock towers, some suspension components and in lower pillars,” he says, noting the metal could be used in instrument panels in the near term if its price came down.

“We can push the envelope and make experimental door inner panels, but magnesium will never be cost-competitive with steel,” Zaluzec adds.

General Motors recently ended production in China of the Cadillac SLS, which had a decklid with a magnesium inner panel made in a GM facility using 50% less heat than is conventionally used in forming high-strength steel stampings.

GM researcher Jon Carter says the use of magnesium for that application stopped when the SLS went off sale in late 2012. But he says the automaker is using the metal in steering wheels, instrument panels and roof-panel frames.

“Probably every car in the GM portfolio has some die-cast magnesium (content),” he says, adding. “Magnesium is just one of many candidates for lightweighting.”