Innovative materials allow automakers to attract buyers

February 2014 - As the automotive sector steadily recovers in 2014, many industry analysts predict vehicle production will reach record levels by the end of the decade. Much of this growth will be a result of pent-up demand from both new buyers and lease returners, given that the average age of all light vehicles on the road increased from 11.2 years in 2012 to 11.4 years in 2013.

Morningstar Inc., Chicago, estimates 16 million units of pent-up automotive demand, according to Richard Hilgert, securities analyst, automotive, who presented at the 7th North American Steel Conference, held in November 2013 in Chicago. This backlog is due to myriad factors, including an increase in both miles driven and average vehicle age. In addition, total vehicle population is still down from the peak in 2009, while the number of licensed drivers continues to grow. High used car prices are also encouraging consumers to buy new cars. “The less the difference between new and used pricing, the more consumers will choose new for the warranty,” Hilgert said.

Better economic conditions will contribute to increased sales, as well. Before the crash, home equity loans were “a major source of funding for new car purchases,” Hilgert noted. Today, home prices are on the rise, which may allow “consumers to tap into the home equity piggy bank to purchase new cars.”

However, despite some improvement in the economy, the slow pace of growth will be the main drag on automotive sales, according to Edmunds.com. There are still a fair number of sidelined buyers, “including young people, lower-income households and small businesses.”

HSS steps up to the plate

As buyers return to dealers’ lots, they’re finding safer, more fuel-efficient vehicles. Evolving regulations are pushing automakers and metals producers to work together to develop new materials to meet these standards. New European regulations for tailpipe emissions will come into effect in 2015, and U.S. regulations for tailpipe emissions and fuel economy will come into effect in 2021. Even tougher standards are being considered.

Developing and producing high-end products, including high-strength automotive steels, is one of the industry’s competitive advantages, said John Ferriola, CEO and president of Nucor Corp., Charlotte, N.C., in his presentation at the North American Steel Conference. 

This past summer, ArcelorMittal, Chicago, unveiled a new ultra-lightweight car door solution that used a combination of advanced high-strength steels and ultra high-strength steels. This includes MS 1500 and Usibor for structural parts, and dual-phase steels such as FF289DP for the outer panel. Using these materials in the door reduced weight and costs by 27 percent without compromising safety and structural requirements. The company indicated further weight savings will be possible with new steel grades that are in development and will be available by 2017. 

The company’s hot stamping steels, such as Usibor 1500, also are being used in the new Volkswagen Golf VII, which is up to 100 kilos lighter in weight than the Golf VI. Armin Plath, Volkswagen’s head of materials research and manufacturing, said in a January 2013 press release following the Golf VII’s launch, “Volkswagen is using high-strength steels in increasing amounts. It is a very cost-effective way of reducing weight. Using new innovations in steel engineering ... it is possible to reduce weight without the use of more costly materials such as aluminum and carbon fiber.”

In addition to helping engineers design lighter cars, AHSS can be used to increase vehicle performance. North Carolina-based Mack Trucks, which is part of the Volvo Group, won the 2013 Swedish Steel Prize for its new wheel suspension, which replaced conventional leaf springs with two Y-shaped components made of AHSS. 

“The design of the suspension requires the blade to flex in the lateral (side-to-side) direction,” says Greg Kiselis, principal engineer, Mack Trucks. “The blade needs to be strong enough to carry the vertical (up/down) and fore/aft loads but soft enough to flex laterally, similar to a leaf spring. High-strength steel is required to carry the load while still allowing the blade to be thin enough to flex.”

He says this is the first suspension that uses two blades. “The blade is unique in that it is a stamping made from 700 mPa (100 ksi) Domex 100 XF. The combination of good forming properties, excellent fatigue properties and consistent material properties are required to make consistent parts.”

The new design provides improved driver comfort and roll stability in addition to reduced braking distance and bogie weight. Tire wear also is reduced, which leads to improvements in transport economy and environmental performance. The suspension has been fitted to the Mack Pinnacle, a truck designed for hauling heavy loads over long transcontinental routes in North America. 

“Although it’s currently being used on a heavy truck, the Twin Y concept could be applied to smaller vehicles, such as medium- or light-duty trucks,” says Kiselis. “Actually, any vehicle with a solid rear axle could take advantage of the Twin Y benefits,” he notes. “To make it work would require adjusting the characteristics of the blades and the bushings that mount the blades to the axle.”

Benefits of aluminum and magnesium

In addition to innovative uses for advanced and ultra high-strength steels, engineers are choosing aluminum and magnesium to reduce overall vehicle weight. Ford’s 50th anniversary Mustang will shed 200 pounds from its curb weight by featuring aluminum front fenders in addition to its existing aluminum hood. “When performance cars like the 2015 Mustang employ low-weight designs with aluminum, they are able to accelerate more quickly, brake in shorter distances and handle the corners better than their heavier, less-efficient counterparts,” according to the Aluminum Association.

The redesigned Mercedes-Benz C class, which debuted in Detroit at the 2014 North American International Auto Show, is 220 pounds lighter due to a hybrid body structure made of 48 percent aluminum. The structure will contribute to a 20 percent cut in fuel consumption without a decrease in power. The vehicle’s suspension is mounted on aluminum die-cast elements that the automaker says are much more rigid than the steel components used on the current model.

Magnesium is another option to help lower weight in vehicles. Mike Schultze, executive vice president of the International Magnesium Association, Wauconda, Ill., points out many automotive manufacturers are choosing to make parts out of magnesium, including “steering wheels, door frames, seat frames, cylinder head covers, crankcases and wheels.”

The IMA notes that magnesium use in automotive applications is increasing, and Schultze says factors that will drive future growth “will be cost, availability and effectiveness in meeting the automakers’ objectives.” He points out a great deal of research and development regarding “expanding the use of magnesium in vehicle construction is being done by IMA members as well as organizations such as the United States Automobile Materials Partnership LLC.”

Gearbox housings, transmission housings and instrument panels can be made with cast magnesium parts. “In the development of new concept cars, automakers are pursuing different solutions in their quest to make vehicles lighter,” Schultze says. The Volkswagen XL1 concept car, for example, has magnesium-forged wheels, magnesium-alloy-cased transmission housing and a steering unit with magnesium sheets. “Some automakers are focusing their efforts on carbon fiber composite materials while others are including magnesium, aluminum and other alloys in their research and development,” he notes.

The future of material use

At the Worcester Polytechnic Institute, Worcester, Mass., Diana Lados, associate professor of mechanical engineering, is conducting research that addresses questions regarding performance and reliability of transportation vehicles and energy savings using an integrative approach to sustainable materials and structural design and manufacturing. 

Lados, who is also the founding director of the university’s Integrative Materials Design Center, recently received the inaugural Constance Tipper Medal from the World Academy of Structural Integrity for her research and contributions in the fields of metal fracture and fatigue and her efforts to transfer this knowledge to industrial applications. In addition, she is the recipient of a five-year $525,000 CAREER Award from the National Science Foundation, which, she notes, “is aimed at boosting vehicle energy efficiency and decreasing greenhouse gas emissions by replacing heavy fatigue-critical structural materials, like steel and cast iron, with lighter metals such as aluminum, titanium and magnesium.”

Lados says this research will help automakers meet CAFE standards for all new cars and light-duty trucks, which were set to 54.5 miles per gallon by 2025. She points out each 10 percent reduction in vehicle weight results in a 5 percent to 8 percent increase in fuel economy and corresponding reductions in CO2 emissions.

“One way to reduce vehicle weight is to replace ferrous materials in structural components with well-engineered lighter metals,” she says. “In structural components, the dynamic properties and fatigue performance of the materials are critical considerations because more than 90 percent of all mechanical failures are fatigue related. Therefore, a transition to lighter metals in such applications needs to be based on a robust fundamental understanding and optimization of the dynamic response and fatigue performance of these materials.”

Using accurate life-prediction tools can also help reduce vehicle weight by allowing designers to construct vehicles “with a higher degree of confidence,” Lados says. The ability to access fatigue data and interpretations of this data means they can apply “sufficient” but not “excessive” safety factors, “which will result in further weight, energy and cost reduction.”

Understanding materials’ fatigue mechanisms at the micro- and nano-structural scale, “will lead to an increased use of lightweight metals like aluminum, titanium and magnesium in cars, trucks, airplanes, boats and other transportation applications.” In addition, Lados says, this knowledge will help metals producers “ develop and optimize new, lighter alloys for current and future transportation applications where light metals are not used extensively or to their highest potential today, while also permitting designers to more accurately predict the lifespan of light-metal components used in high-integrity, fatigue-critical applications. Thus, the results of this work will have an important impact on both materials processing and design communities, and ultimately on the environment and society.” MM