The Case for Aluminum in Lightweighting Electric Vehicles
September 7, 2012
By:  Jim Motavalli

It’s all about the weight. The range of an electric car is determined by a simple formula involving mass and inertia and some other things I’d have known if I’d paid attention in physics class. The bottom line is that reducing that mass pays big dividends—either greater range or a lower price because of a smaller battery pack and electric motor.

Not the New Kid on the Block

The aluminum industry thinks it has the answer to a green automaker’s prayers. Aluminum is not a new high-tech miracle material like carbon fiber (used for the body structure in the electric BMW i3 “Megacity” vehicle); it’s been around since the dawn of the auto age. But Randall Scheps, director of ground transportation for Alcoa and chairman of the Aluminum Association’s automotive group, thinks it’s due for a renaissance, and he’s willing to trample all over the alternatives—including the aforementioned carbon fiber and high-strength steel—to make his case.

“In electric cars, every 10 percent of weight reduction can reduce battery size four to six percent, or give you a 10 percent improvement in range,” Scheps said. “And because lithium-ion batteries are so expensive, still around $750 per kilowatt-hour, every dollar invested in light-weighting saves you $3 in battery costs.”

The Tesla Model S, with an all-aluminum structure, is the industry’s poster child. With its big battery capacity, the car weighs a not-inconsiderable 4,647 pounds, but Scheps estimates it would be over 5,000 with a body in steel. Tesla’s Roadster and the Fisker Karma also use extensive amounts of aluminum.

The Magic Bus

To demonstrate what it can do, Alcoa built an aluminum body for the battery-powered BYD Electric Bus that reduced weight 10 percent from its existing steel platform, and also increased range 10 percent, to 200 kilometers. That bus is going into production in China, and is also likely to appear on other world markets.

The-54.5-mpg-by-2025 Corporate Average Fuel Economy (CAFE) standards are a boon to aluminum and other lightweight materials. “We anticipate that the use of aluminum sheet will triple by 2015 because of CAFE,” said Libby Archell, an Alcoa spokeswoman. Aluminum sheets are used to make hoods and trunks and other non-structural parts, which are the parts of the car most commonly made from the material. Thirty percent of all car hoods today are made from aluminum, and the industry expects that to grow to 50 percent by 2050.

The Audi A8 is a good example of a car that mixes big dollops of aluminum with the steel, and it’s a model for what we’re likely to see going forward. The new Cadillac ATS also makes extensive use of aluminum, including hood, front suspension, engine block and transmission, wheels and shock tower castings. The material will be used not only for under-hood components, but for body parts and, increasingly, entire platforms. The 2012 Mercedes SL has the company's first-ever all-aluminum body, saving 300 pounds. It's the lightest SL ever produced. Want more? The new Range Rover is all-aluminum, too, with a 20 percent weight savings over outgoing models.

The Cost Barrier

But if aluminum’s been around forever, why isn’t it already being used extensively? That’s a simple one: cost. There’s still a bare minimum $100 per-car cost premium for a body in aluminum, even when the savings from a smaller drivetrain, brakes and transmission are factored in, and Scheps admits that, “pound for pound, we’re not going to close the price gap with steel.” CAFE mandates make the extra investment worthwhile.

BMW is preaching the weight-saving mantra, but is addressing it with a complicated carbon fiber supply chain that sees Japanese-made fibers shipped to Washington State to be made into sheets, then to Germany for finishing.

Carbon fiber is lighter than steel or aluminum, but stronger than either one. But Scheps is ready with an argument. “Carbon fiber has some fundamental issues that will keep it from mass penetration in the auto market,” he said. “It’s too expensive and the cycle times are too long—if it takes five to 10 minutes to make a single part, it creates huge problems in the supply chain. Plus there are recyclability and repairability issues. Carbon fiber doesn’t crash in a predictable way; it shatters and panels made from it are often not repairable.”

What about high-strength steel, which is that industry’s bid to grab onto the light-weighting boom? Scheps has got that one covered, too. “We did a study about a year ago and found that with high-strength steel in a best-case scenario, you could have maybe 11 percent of weight reduction,” he said. “With aluminum, the potential savings was 40 percent.”

The Aluminum Association Makes the Case:

  • Using aluminum in an electric car can save $3,000 per vehicle, because of reductions in required battery size (down up to 10 percent);
  • The driving range can be improved approximately equal to the mass saved—cut weight 20 percent, go 20 miles further.


That’s the industry’s case. The steel and carbon-fiber industries can and do make convincing arguments to the contrary. Carbon fiber prices are quite likely to come down, especially if current research bears fruit. And steel will always have huge price advantages. The industry counters all of the arguments for aluminum. It claims that advanced high-strength steel can deliver a car with 30 percent weight savings over conventional models, with costs that are 30 percent lower than a comparable aluminum-bodied car.

More than 70 percent of the Chevy Volt’s structure is high-strength steel. Hyundai, which has its own steel plant, has also done a lot with high-strength materials. The Hyundai Santa Fe owes its weight savings—approximately 450 pounds less than most of its competition—because of high-strength steel. And part of Mazda’s Skyactiv approach is saving weight with lightweight steel platforms.

Some of the best innovation uses aluminum and steel together. The new 2013 Honda Accord features the world’s first use of a steel-and-aluminum bonded front subframe. Combining the best of both metals saves 13 pounds in that application.

Other tech isn’t standing still, but the aluminum argument goes beyond hype and is likely win fans and influence engineers in the run-up to the CAFE mandates. And any benefits for internal-combustion cars are 2X or 3X on EVs.

Photo by:
BYD needed help in reducing weight on its electric city bus; aluminum saved the day, with a 10 percent savings. (BYD photo)



Photo by:
Tesla's Model S uses a lightweight aluminum structure, and that was key to achieving range goals. (Tesla photo)



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