Although cars have been around for more than a century, the material they are made of (steel) has mostly stayed the same. It has only been in the past few decades that advanced materials ranging from aluminum and magnesium alloys, to carbon fiber composites, have made their way into mass-produced passenger cars.

Advanced materials are essential for boosting the fuel economy of modern automobiles while maintaining safety and performance. Because it takes less energy to accelerate a lighter object than a heavier one, lightweight materials offer great potential for increasing vehicle efficiency. A 10% reduction in vehicle weight can result in a 6 to 8 percent fuel economy improvement. Replacing traditional steel components with lightweight materials such as high-strength steel, magnesium (Mg) alloys, aluminum (Al) alloys, carbon fiber, and polymer composites can directly reduce the weight of a vehicle’s body and chassis by up to 50 percent, and therefore reduce a vehicle’s fuel consumption. Using lightweight components and high-efficiency engines enabled by advanced materials in one-quarter of the U.S. fleet could save more than 5 billion gallons of fuel annually by 2030.

By using lightweight structural materials, cars can carry additional advanced emission control systems, safety devices, and integrated electronic systems without increasing the overall weight of the vehicle. While any vehicle can use lightweight materials, they are especially important for hybrid electric, plug-in hybrid electric, and electric vehicles. Using lightweight materials in these vehicles can offset the weight of power systems such as batteries and electric motors, improving the efficiency and increasing their all-electric range. Alternatively, the use of lightweight materials could result in needing a smaller and lower-cost battery while keeping the all-electric range of plug-in vehicles constant.

Scientists already understand the properties of these materials and the associated manufacturing processes. Researchers are working to lower their cost and improve the processes for joining, modeling, and recycling these materials.

The U.S. Department of Energy’s Vehicle Technologies Office (VTO) develops advanced materials that help boost the fuel economy of modern vehicles, while maintaining safety and performance. Further developing advanced materials requires increasing understanding of their composition and morphology. Computational materials science should bring advanced materials into the market much faster than in the past. Researchers can also use computational approaches to create vehicle designs that maximize the potential of these materials. To improve these tools, VTO works with the Lightweight Materials National Laboratory Consortium (LightMAT), a network of 10 national laboratories with technical capabilities highly relevant to lightweight materials development and utilization.

Research and development into lightweight materials is essential for lowering their cost, increasing their ability to be recycled, enabling their integration into vehicles, and maximizing their fuel economy benefits. Although many materials show promise in reducing vehicle weight, there are pros and cons to each, ranging from production costs to property deficiencies.

Advanced High-Strength Steel: Pillars and door rings

Stronger and more ductile than typical steel, advanced high-strength steel could reduce component weight by up to 25 percent, particularly in strength-limited designs such as pillars and door rings. It is generally compatible with existing manufacturing and materials currently used in vehicles.

Pros: High strength, stiffness, formability, and corrosion performance, as well as low cost.

Cons: High cost, and wears out stamping molds faster than for lesser grades. Ductility decreases as strength increases, adding issues in forming and joining. Challenges also include design, component processing, and behavior in harsh environments.

The Audi A8L features a mix of steels, aluminum, polymers, and magnesium. These metals are increasingly used on the components of powertrains
The Audi A8 L features a Multimaterial Space Frame that relies on a mix of steels, aluminum, polymers, and magnesium. (©Audi AG)

Aluminum: Powertrains, vehicle Hoods, and Panels

Because of aluminum’s use in aerospace and construction, scientists have a good understanding of its characteristics and processing. Manufacturers currently use it in vehicle hoods, panels, and powertrain components, but face barriers in cost and manufacturing. Manufacturers also face issues with joining, corrosion, repair, and recycling when they combine aluminum with other materials. A lighter, more expensive alternative to steel, aluminum is increasingly being utilized for hoods, trunk lids, and doors, and has the potential to reduce weight by up to 60 percent.

Pros: Technology is fairly mature; good stiffness, strength, and energy absorption.

Cons: Higher cost than steel, joining to other materials, and limited formability issues.

Magnesium: Powertrains and sub-assembly closures

With the lowest density of all structural metals, magnesium alloys have the potential to reduce component by weight up to 70 percent. Magnesium is presently used in castings for power-trains or sub-assembly closures. The increased use of magnesium for automotive applications is limited by several technical challenges. Even though magnesium (Mg) can reduce component weight by more than 60 percent, its use is currently limited to less than 1 percent of the average vehicle by weight. Although incorporation of multiple, individually cast, or wrought Mg components into articulated sub-assemblies appears unlikely in the near-term, Mg will continue to have a role in vehicle lightweighting, predicated on its attractive features of low density, high specific stiffness, and amenability to thin-wall die casting and component integration.

Pros: High stiffness and strength, compatible with existing infrastructure for stamping.

Cons: Expensive, lack of availability from U.S. manufacturers in large quantities to meet automotive needs. Other challenges include ductility, joining, repair, recycling, and corrosion. Rare earth additives may also be needed to improve energy absorption to meet crash requirements.

The Ford Escape features aluminum wheels. Alumnium is increasingly used to make powertrains, driveshafts, differential gears, and transmissions.
The Ford Escape features machined-aluminum wheels. (©The Ford Motor Company)

Carbon Fiber Composites

While manufacturers use carbon fiber in high-performance vehicles, the expense of the input material and process to develop it are generally too high for use in popular models. Despite being half the weight of steel, carbon fiber composites are four times stronger and have the potential to reduce vehicle weight by up to 70 percent.

Pros: High stiffness, high strength, enables the manufacture of highly complex shapes, and offers tremendous weight savings.

Cons: High production cost of carbon fiber and difficulty joining into vehicles, along with associated challenges in modeling performance, infrastructure, and sufficient amounts of fiber to meet automotive needs.

Titanium: POwertrains, valves, springs, suspensions

This high-temperature metal is used in powertrain systems to reduce weight by up to 55 percent. Titanium is also used in valves, springs, suspensions, wheels, and gearbox housings.

Pros: High strength-to-weight ratio, can withstand high temperatures.

Cons: High cost of materials, and formability challenges.

Conclusion

Lightweight structural materials — advanced high-strength steel, aluminum, magnesium, and carbon-fiber polymer composites — enable improvements in fuel economy by providing properties that are equal to or better than traditional materials, and by providing flexibility in design that enables additional lightweighting.

Although each lightweight structural material has strengths and weaknesses that render it more suitable for certain applications than others, the most effective way of reducing the overall weight of a vehicle is to use the right structural material for the right application. Multi-material crosscutting endeavors must include evaluations of both safety and cost.

For more information, visit the DOE’s Vehicle Technologies Office here .


Tech Briefs Magazine

This article first appeared in the March, 2018 issue of Tech Briefs Magazine.

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