Future pickups: Steel or aluminum?

By Christopher A. Sawyer
The Virtual Driver

(June 29, 2014) First, Ford stunned the industry with the announcement that its mega-successful F-150 pickup would be shifting from steel to aluminum body construction. (Ford doesn’t break out specific models like the F-150, but a good rule of thumb is that it accounts for about 2/3, or about 534,000 units, of Ford’s 800,000-unit F-Series sales volume.)

Then came rumors that GM would be following Ford’s lead, despite just launching a two-truck strategy built around conventional full-size pickups and lighter, more fuel-efficient midsize pickups.

The only company that seemed wedded to steel was Chrysler, whose all-steel Ram 1500 is lighter than most of its competition. Yet even that bubble was burst when a study by Drucker Worldwide claimed that 70% of new pickup trucks will be aluminum-bodied by 2025. Suddenly it looked like the only large-scale steel on future pickups would be in the frame.

There’s only one problem. There are no firm plans for 2025 model year pickups in place, though there are many ongoing engineering studies. Decisions on what materials will be used won’t begin to be settled until 2020 at the earliest.

“We’ve had incursions like this before,” says Ron Krupitzer, vice president, Automotive Market, Steel Market Development Institute (SMDI), “though in the past it was composites and plastics with vehicles like the Pontiac Fiero, Saturn and GM’s APV minivans.”

Unfortunately, GM’s hopes for improved cost and quality didn’t pan out. “There was too much given up for the economies they thought they were going to gain.” Might the same be true of Ford’s shift to aluminum? “Certainly it has caught our attention but, to be honest, we’re a little puzzled. With the weight reduction achievable with high-strength steel — which is very, very close to aluminum in many cases — the ultimate difference in weight and fuel saved in the real world is fairly small.”

According to SMDI estimates, reducing the weight of a vehicle by 10% brings a 3% reduction in fuel consumption. “That’s a tank or two of fuel over the life of most full-size vehicles,” says Krupitzer. However, starting from a clean sheet, and sizing the powertrain to give you exactly the same payload and acceleration that you had in the heavier version brings the fuel economy improvement up to 7%.

Ford has done just that with the 2015 F-150 by switching to a clean-sheet aluminum body design and using an optimized 2.7-liter EcoBoost V6 in the most economical versions. Some insiders suggest Ford is targeting a 10% fuel economy improvement, but the 7% number cited by Krupitzer is a good rule of thumb. This would put Ford’s fuel economy improvement at twice what most automakers switching to lighter weight steel formulations traditionally have gained.

“Our current work and research on new grades show that applying steel technology can save the weight required to get car companies to the mass and fuel economy goals they are targeting in 2025, and at a lower cost [than aluminum],” says Krupitzer.

And while this may seem a bit hard to believe, David Anderson, Automotive Technical Panel, Long Products Program, SMDI puts it all in context. “The Cadillac ATS is the most optimized steel-bodied vehicle currently in production.” It has an average steel strength of about 410 MegaPascals, but that is just over half that of the steel used in the Future Steel Vehicle concept. There’s a lot of room left for lightweighting. “Over the years we have been very good at making the evolutionary changes that allow OEMs to meet their next, short-term weight reduction goal (the 3%-4% mentioned earlier),” says Anderson, “and this has created the impression that steel is only capable of making incremental improvements.”

Krupitzer and Anderson also suspect there’s insufficient appreciation for the fact that aluminum gets its strength via lower density, while steel does the same through stronger, thinner-gauge materials. This has led steel makers to invest heavily in computer-aided design and engineering.

“Varying the architecture for greater efficiency,” says Krupitzer, “brought us to topology optimization; looking at the package space, subtracting that away, and optimizing the remaining structure. This results in some very interesting solutions that are quite effective. Even though the gauge is thinner, we use the geometry to restore or enhance stiffness.”

This has resulted in what he describes as the front primary load path “elephant nose” structure of the Future Steel Vehicle, and roof bows that travel diagonally instead of laterally from span-to-span. This is combined with weld bonding — welding and gluing panels at the same time — in order to get a continuous join that is many times less expensive than laser joining.

Anderson admits that, “these tools are applicable to all OEM designs and materials, and those material providers would gain from the same clean-sheet approach and topology optimization we have used with our advanced steels.”

However, whereas aluminum still uses the same 5000 and 6000 series alloys they’ve traditionally offered to both automotive and military users for years (Krupitzer likens referring to the alloys used in the 2015 F-150 as “military grade” to the fishing industry’s renaming of the Patagonian toothfish as “Chilean Sea Bass”), steel potentially has more to offer on the materials front.

“Our current portfolio includes 45 advanced high-strength steels, and approximately 19 manufacturing techniques like roll-forming, tailor-rolled blanks and hydroforming that other materials can’t match. And we don’t need five years to build extra capacity like the aluminum providers. We have it in place now.” It is this new aluminum production capacity that the steel folks believe will fall well below that predicted will be necessary in the recent Ducker Worldwide study.

The Virtual Driver