Five grades of high-strength low-alloy material, plus aluminum, pump muscle into the full-size Chevrolet pickup without adding heft 

May 2019 - A corporate change of mind at General Motors Co. has produced a new pickup truck that incorporates arguably the most high-strength low-alloy steel of any vehicle in the full-size pickup market. The 2019 Chevrolet Silverado (and its GMC Sierra counterpart) contains nearly 64 percent high-technology steels; and 21.6 percent is conventional mild steel and 14.5 percent is aluminum.

The weight savings are dramatic.

The total base curb weight of the new crew cab model is 4,796 pounds (2,175 kilograms) for the two-wheel drive version. That is a reduction of 450 pounds (204.1 kg), with less than one-eighth of the structure made from aluminum. Maximum payload is rated at 2,180 pounds (989 kg), for a gross vehicle weight rating (GVWR) of 7,100 pounds (3,220.5 kg).

The front of the 2019 Silverado is an integral, welded structure, converted from a bolted assembly in the 2018 model. Mass savings is 15 percent. Silverado High Country Crew Cab courtesy of Walker Chevrolet, Franklin, Tennessee

Monster market

Pickup trucks are a monster market, the competition is ferocious, and the passionately partisan customer base tolerates no missteps with their favorite make. To show how dependent automakers are on light trucks, the online service Statistics Portal reported that in the U.S. last year, 11.9 million pickups were sold out of total retail sales of 17.2 million units. That’s a 70-percent chunk of the vehicle business.

GM’s original plan was to build an aluminum-intensive vehicle to compete head-on with Ford Motor Co. The Blue Oval converted to an all-aluminum body for the 2015 model year, with the frame remaining steel. (The May 2017 issue of FFJournal, Modern Metals’ sister publication, detailed this project.) Ford’s effort produced a standard cab body-in-white weighing 660 pounds including closure panels, 700 pounds less than the all-steel version.

On their own

GM is a frequent partner with the Steel Market Development Institute in design and engineering projects. (The SMDI is a business unit of the American Iron and Steel Institute.) But this time they ventured out on their own, according to Jody N. Hall, Ph.D., vice president of automotive market for the SMDI.

“The automaker would typically submit a design, and we would provide different grades of steel and their properties. Usually, we hire a third party engineering firm to optimize our materials. Because of all the collaborations we’ve done with GM over the decades, they have the latest and greatest technology in steel.”

Shelving an all-aluminum structure for a combined steel/aluminum build is a no-brainer for the understandably partisan Hall. “We did a cost estimate that priced aluminum at $1,200 per vehicle just for materials,” she states. “That much money buys a lot of other technology that you can put into a truck.

“We think that the only benefit you get from all that extra cost is a very small improvement in fuel economy. With gas prices as low as they are, consumers can never get their investment back through savings at the pump.”

New take on an old material

The SMDI emphasizes the lower cost of steel, even high-performance grades. “The auto industry’s infrastructure is set up for steel,” Hall points out. Nevertheless, she concedes, conventional tooling, presses and skills require revisions for HSS. “The tooling has to change, and the presses needed are generally higher tonnage. Design of the parts has to change also,” she adds.

Material thicknesses are reduced, and wear on the dies is accelerated with high-strength steels. Tooling wear is also a factor with aluminum, due to the presence of abrasive oxides.

“The tooling costs for HSS and aluminum are about the same,” Hall continues, “but aluminum is not as compliant for complex shapes as steels. In aluminum, you may have to either change your design or break up a component into a multiple-part assembly to produce the same shape.”

Great Designs in Steel

Chevrolet shared much of its technical data on the Silverado with the SMDI’s Great Designs in Steel seminar, held last May in Livonia, Michigan. Jeff Sulik, engineering group manager, and Joy Geeraerts, senior design release engineer, both from the GM Technical Center in Warren, Michigan, were the presenters.

The high-tech steels in the Silverado, they said, are divided into five categories. HSLA and bake-hardenable steels are 39.4 percent; advanced high-strength steels (AHSS) are 11.9 percent. UHSS or ultra high-strength steels are 7.2 percent, and press-hardened steel (PHS) is 5.5 percent. (See sidebar, page 17.) The vehicle has a traditional body-on-frame architecture, and the frame also incorporates HSLA steel.

The mass reduction in the frame is 88 pounds (40 kg), and frame construction incorporates six manufacturing processes. Weldments, roll forming, hydroforming, tailor rolled parts, aluminum extrusions and formed tubing all make up the ladder frame.

HSLA grade 500 is used for the truck bed, which allowed reducing the metal thickness from 0.037 inch (0.95 mm) to 0.033 inch (0.85 mm). A nearly 0.004-inch (0.10 mm) reduction had no effect on structural performance. Sulik and Geeraerts report that puncture and impact strength are the same as last-year’s version.

Aluminum for closures

Aluminum hasn’t been ignored. Hoods, doors and tailgates consume both 5000- and 6000-series alloys, with a weight reduction of 92.9 pounds (42.1 kg). While the aluminum hood cut only 1.3 pounds (0.6 kilograms) from the cab, the tailgate trimmed mass by 21 pounds or 9.5 kg from the bed.

Manufacturing technology also contributed to mass reduction. The rear frame side members are tailor rolled blanks, and roll forming produces the front and rear tips and mid-rails.

The bolted front assembly of the 2018 Silverado has been replaced with an integrated stamped and welded structure for 2019, and the front end employs  adhesive bonding. Mass savings: 15 percent over the prior year’s model.

The new front end, according to Chevy engineers, has higher dynamic stiffness for improved ride and handling, and a more quiet cabin interior. Lateral bending strength of the front-end structural module is 21.8 Hertz, global vertical bending is 20.9 Hertz, and global torsion is 29.8 Hertz. These numbers outperformed competitive benchmark data, Sulik and Geeraerts emphasized.

Long lasting

Chevrolet promotes the Silverado as “the longest-lasting full-size truck on the road,” pointing out that improved cab sealing “enhances corrosion resistance.” Sealer is applied both before welding and on the paint line, and double-sealed flanges prevent water intrusion on both sides of flanges. Compared to the 2018 Silverado, almost 20 pounds (9 kg) of sealer have been added, totaling 111.5 feet or 34 meters.

The 2019 Silverado is taller than its predecessor, and the wheels have been moved forward for a reduced front-end length. Nevertheless, the wheelbase is 4.5 inches longer and overall length rose 1.5 inches, increasing both passenger volume and cargo room. Cab space is up, providing more comfortable seating. In spite of the higher structure, aerodynamics are improved 7 percent.

With its investment in HSS, why hasn’t Chevrolet capitalized on what it considers a competitive advantage? “Actually, they have,” said Gary Mason, manager of automotive communications at the SMDI. “Remember the toolbox dropped in the bed? But they seem to be promoting steel generically, not the attributes of high-performance metals.”

A cutaway of the all-new 2.7-liter turbo engine found in the Chevrolet Silverado, illustrated by David Kimble.

The next 100 years

The new Silverado was launched in December 2018 during an event at Texas Motor Speedway in Dallas, commemorating 100 years of Chevrolet trucks. The Silverado was also featured at Detroit’s North American International Auto Show in January, and at the Chicago Auto Show a month later.

The GM division inaugurates its second 100 years of light truck production with a technological tour de force in design and engineering. Some 85 million trucks have been built since 1919, and The General’s design and manufacturing prowess seems poised for 85 million more. MM