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Downsizing through unibody construction, aerodynamics lead lightweight charge


Every bright spot comes with a dark side. Such is the case with the auto industry's efforts to slim down vehicles to improve fuel economy and meet ever-tightening emissions standards. Automakers are racing to incorporate lightweight materials to meet their goals, but some of the lightening efforts come with serious sticker shock.

"The use of advanced materials such as magnesium, aluminum and ultra high-strength boron steel offers automakers structural strength at a reduced weight to help improve fuel economy and meet safety and durability requirements," said Robert Parker, director of product communications at Ford Motor Co., Dearborn, Mich.

High-strength steels (HSS) played prominently in the efforts of Japan's Mazda Motor Corp. to shave more than 220 pounds off its much-anticipated 2010 Mazda2 subcompact compared with its predecessor. And Tokyo-based Nissan Motor Co. Ltd. slimmed down its new 370Z roadster by 95 pounds thanks to a wider application of HSS, and for the first time aluminum door panels, an aluminum hatch and an all-aluminum hood (the previous aluminum hood design utilized steel reinforcements).

"We are working to reduce the thickness of steel sheet by enhancing the strength, expanding the use of aluminum and other lightweight materials, and reducing vehicle weight by rationalizing vehicle body structure," a Nissan spokesman said. The automaker has committed to reducing the weight of its vehicle fleet by an average of 15 percent by 2015 from its 2005 models.

Aluminum and advanced high-strength steels (AHSS) are expected to figure prominently in General Motors Co.'s future. The Detroit-based automaker's use of AHSS is expected to top 120,000 tonnes in 2010, up from less than 10,000 tonnes in 2004, according to the American Iron and Steel Institute.

Aluminum, meanwhile, will be making its way into the wheels, blocks, hoods, tailgates and bumpers of GM vehicles at an increasing rate, according to Mark Verbrugge, director of the Chemical Sciences and Materials Systems Laboratory at GM's Research and Development Center. "We use a lot of aluminum today—about 300 pounds per vehicle—and are likely to use more lightweight materials in the future," he said.

Composites also are making inroads into automotive design, albeit it at a slower pace than AHSS and aluminum.

Magna International Inc., Canada's biggest auto industry supplier, has announced plans to create a $7.2-million research facility in collaboration with the Canadian government that would develop auto parts technology using lightweight composites.

The U.S. Energy Department's Oak Ridge National Laboratory in Tennessee was recently allocated $34.7 million to establish the Carbon Fiber Technology Center to identify and develop low-cost carbon fiber automotive applications.

The challenge many of these alternative materials face, however, is cost. A Porsche Cars Canada Ltd. spokesman noted that while carbon fiber, magnesium and aluminum have shown promise, their price tags can be intimidating to automakers.

Automotive steel for the most part is still relatively cheap, with hot-rolled band, used for vehicle body panels, costing an average of 23 to 27 cents per pound, according to industry estimates, with high-grade steel about 10 to 30 percent more expensive. Aluminum, however, can cost upward of $1 per pound, while magnesium is often above $2 per pound and carbon fiber, in some cases, can cost four to eight times more than magnesium.

"While carbon-fiber is sexy, it is expensive, difficult to work with and doesn't make sense for a mainstream car," the Porsche Canada spokesman said, noting that the Mississauga, Ontario, automaker's new Panamera four-door sedan optimizes different grades of steel. The company also has targeted aluminum use in its door skins and hood, with magnesium used in its bumper carriers and door frames, but to a more limited degree. "The way magnesium is used, because it's difficult to work with and expensive, is something that I'd be surprised to see in such a great extent in any other cars."

While lightweight metals might continue to grab the spotlight, many auto executives expect some of the more notable changes to be in size, not substance.

Several analysts believe that weight reduction, including segment shift to different vehicles, will account for only one-quarter of the overall fuel economy improvement and carbon dioxide reduction required by 2020. The remainder will come from powertrain changes, aerodynamic improvements, low-rolling-resistance tires and battery improvements.

Parker expects to see more platform shifts from body-on-frame—where a vehicle's body and bed are separate components bolted on top of the frame—to unibody designs.

Verbrugge said he expects automakers to continue their focus on smaller vehicles, which will reduce the volume of certain materials required in manufacturing. He noted that the majority of Chevrolet, Buick, GMC and Cadillac vehicles in coming years will be cars and crossovers. "Trucks still are an important part of our portfolio, but we expect they will largely return to their original customers—those using them for work or specific needs." he said. DARCY KEITH

Jamie Zachary contributed to this story.

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