Read Part 1, Part 2, Part 3, Part 4 and Part 6 of this series.
When it comes to improving fuel economy, engines, powertrains, fuels and batteries seem to get all the attention.
But what about the car's traditional steel side panel or rooftop?
Using advanced lightweight materials on even the most basic car parts can improve overall fuel efficiency, too. According to the Department of Energy, reducing a vehicle's weight by 10 percent can improve fuel economy by 6 to 8 percent.
Steel has traditionally made up about 60 percent of a vehicle's total weight. But in order to meet consumer demands and increasingly stringent federal fuel economy standards, automakers are looking to alternatives, including advanced high-strength steel, aluminum, magnesium and carbon fiber.
Lightweight materials are a cost-effective way to boost fuel efficiency on conventional combustion engine vehicles and advanced automobiles like hybrids, electric vehicles and hydrogen fuel-cell vehicles.
"There are literally hundreds of different technologies that can be brought to bear to help improve fuel efficiency, but all of them begin with lightweighting," said Kevin Lowery, a spokesman with the aluminum company Alcoa Inc.
Luxury vehicles, like the Audi A8 sedan, have been using lightweight materials for years so that the car could take on a larger powertrain without adding weight and compromising on horsepower. But a new push for better fuel efficiency across the passenger vehicle fleet has more automakers using these materials across their lineup.
New federal fuel economy standards will require automakers to improve fleet efficiency to 54.5 mpg by 2025. Building upon that progress, Energy Secretary Steven Chu announced seven new research projects last month to accelerate the development of stronger and lighter automotive materials for cars and trucks.
"With strong, lightweight materials, we have an opportunity to dramatically increase vehicle fuel economy while helping America maintain its competitive edge in automotive design and manufacturing," he said following the announcement.
Aluminum in demand; steel gets stronger
Aluminum is the second-most common material in cars on the roads today after steel. But auto manufacturers have said they intend to double their use of aluminum by 2025, Lowrey said.
Ford Motor Co. announced this year it is looking to make the body of its popular F-150 light-duty truck largely out of aluminum, which would reduce the truck's weight by about 700 pounds and produce about 10 percent in fuel savings. On a hybrid vehicle, aluminum could improve the fuel economy by more than 13 percent compared to an equivalent car made of steel, according to Alcoa.
"There's not an OEM [original equipment manufacturer] anywhere in the world that isn't, as we speak, talking to an aluminum company," he said. "In years past, it wasn't that way."
Car components made of aluminum are anywhere between 10 and 40 percent lighter than conventional steel. But aluminum is about 35 percent more expensive than steel, and concerns linger that it might not be as durable.
So steel is still in the game. And new advanced high-strength steels can actually provide up to 35 percent in weight savings, according to the Steel Market Development Institute (SMDI).
The industry achieved these gains using a different chemistry to produce a stronger but more formable type of steel, dubbed "dual phase steel." Making these steels didn't add much any extra cost because it simply required changing the cooling rates on existing process lines, said Ronald Krupitzer, vice president of automotive applications for SMDI.
The industry can now make multiple types of steel that are two to three times stronger than they were a decade ago.
"If you make a component stronger, it can carry the same load as it did before, but you don't need as much steel to do it. You can make parts thinner, but they can absorb the same about of energy and hold the same load," Krupitzer said.
Earlier this month, Volkswagen AG announced that the seventh-generation Golf was 220 pounds lighter than its predecessor in part because it incorporated nearly 15 percent more high-strength steel.
General Motors Ventures, a GM subsidiary created to invest in innovative automotive technologies, announced in August that it was investing an undisclosed amount in the NanoSteel Co., a leading manufacturer of advanced high-strength steel.
Jon Lauckner, president of GM Ventures, said NanoSteel's nano-structured alloys are "a potential game-changer."
So far, crash tests show safety unchanged
But before they can transform the auto industry, both high-strength steel and aluminum have to address concerns that they are as safe as conventional steel parts.
The Department of Transportation and U.S. EPA wrote in the final rule for fuel economy standards from 2017-2025 that they expect lightweighting to play an increasingly important role in helping automakers meet the 54.5 mpg mark.
In federal crash tests, the agencies found that advanced lightweight materials -- in this case a mix of high-strength steel and aluminum, and a small amount of magnesium and composite material -- performed just as well as baseline vehicle models.
EPA and DOT's lightweighting studies showed that a baseline vehicle's mass could be reduced by about 20 percent without affecting its safety performance.
But at the same time, the agencies acknowledged that lightweighting techniques could create concerns that may require extra safety equipment, such as better air bags or seat belts.
Krupitzer admitted lightweight cars could pose safety risks in crash scenarios but said the steel industry has been able to engineer solutions that pass all the existing tests. Vehicles made with high-strength steel even perform better in side-impact and rollover situations, he said.
The aluminum industry has made the same assertions. According to Alcoa, automotive aluminum can maintain or even increase the size and strength of a vehicle's front- and back-end crumple zones, which absorb energy upon crash impact without increasing overall weight. Steel, the group says, cannot.
A palpable sense of competition has risen in the automotive materials industry along with the push for better mileage.
"I can guarantee our competition -- the aluminum, magnesium and plastics folks -- are working real hard to take some of the parts [currently made of steel] and acquire them," Krupitzer said. "And we're working at least as hard, if not harder, to improve on the parts we already have."
In discussions between automakers and Alcoa, Lowrey said that the car companies are deciding whether to bypass high-strength steel altogether and jump to aluminum, which provides better weight savings. They are asking, "Why don't we just get there faster?" he said.
But manufacturers indicated that a universal material substitution -- a complete switch from steel to aluminum in car bodies, for instance -- would not be viable in the 2017-2025 time frame because of cost and engineering barriers, according to EPA and DOT's technical assessment of technologies to meet higher fuel economy goals.
Carbon fiber moves off the race track
Most manufactures said they had already invested in high-strength steel to meet 2012-2016 fuel economy standards, but that a shift may be required to meet more aggressive goals. Most estimated that vehicle mass could be reduced by 10 to 15 percent between 2010 and 2025.
Other advanced materials like plastics, magnesium and carbon fiber may gain more of automakers' attention beyond the 2025 time frame and are already being adopted in parts of the industry.
Today, Ford announced it is collaborating with the company Weyerhaeuser to use plastic composite material car parts made of cellulose fibers from sustainably grown trees instead of fiberglass or mineral reinforcements. Ford research found that the cellulose-based plastic composite met its stringent durability requirements but weighs 10 percent less than the alternative.
Carbon fiber, an ultra-light and durable material, is no stranger on the race track, where speed is paramount and price is no object. But high costs have largely limited carbon fiber to the luxury section of the consumer market.
The passenger compartment of BMW's concept electric vehicles, the i3 and i8, are made entirely out of carbon-fiber-reinforced plastic. The composite material is at least as strong as steel but around 50 percent lighter, and is 20 percent lighter than aluminum, according to the company.
BMW has made big investments in carbon fiber in the hope of bringing down costs. Last year, BMW opened a carbon fiber production plant in Moses Lake, Wash., where it will manufacture the material for the i-class vehicles. The i3 is expected to launch in 2013, and the i8 in 2014.
"Carbon fibers are a key construction material for the automotive industry of the 21st century and will change the way we develop and build cars," said Norbert Reithofer, BMW's CEO and board chairman, upon announcing the new production facility.
The Tesla Roadster, a $100,000 high-performance all-electric sports car, is made with a carbon-fiber body panels and an aluminum chassis for better efficiency. On the new Tesla Model S all-electric sedan, a more affordable option at around $50,000, the company used aluminum for the body but passed on the carbon fiber.
"For limited or low-volume production cars like the Roadster, carbon fiber is a great material to reduce weight. It's not a solution for higher-volume production due to cost and manufacturing time," said Tesla Design Director Franz von Holzhausen in a statement earlier this year. "For Model S, we are using aluminum for the body panels and chassis. Aluminum is as strong as steel but lighter in weight, and has similar manufacturing capabilities. Lighter weight translates directly to efficiency."