More than 72 percent of the cab structure of the 2015 Chevrolet Colorado comprises advanced HSS, according to Jody Hall, vice president of the automotive market for the Steel Development Institute. The center pillar is made with one piece of press hardened Martensitic steel that’s thinner on the top and bottom than in the middle to optimize performance. “They don’t need as much mass in the top and bottom, so there’s less material there,” says Hall. “And in today’s market, every gram counts.” Photo Credit: General Motors
“Only 2 percent of a vehicle’s mass is aluminum structure,” said Bertolini. “The low-hanging fruit has been harvested. Taking simple parts and converting them to aluminum has been done for quite a while. Now the hard part has to be done: We have to design for aluminum.”
Bertolini cites the Cadillac CT6, which debuted in 2016, as an example. The body of the mixed-material luxury sedan is 64 percent aluminum and weighs approximately 200 pounds less than a similar size vehicle using predominantly steel. The structure also uses less parts. For example, the front-door hinge pillars feature 13 high-pressure aluminum die castings, each one replacing 35 steel stampings, according to Motor Trends magazine.
The aluminum industry hopes to gain traction with customers by touting its benefits: short production lead times, low tooling costs, recyclability and the ease with which it can be fabricated into integral shapes. But aluminum faces significant hurdles, many of which will sound familiar to composites professionals. The first is convincing automakers to design for aluminum, rather than simply replace steel components.
Bertolini shared the story of an OEM that asked Pennex Aluminum to convert a steel chassis to an aluminum one. Afterward, the automaker complained that the chassis was still too heavy and it was expensive. “We told the OEM, ‘You must focus on the design point. You have to start over, design for aluminum and take advantage of the geometry,’” said Bertolini. In addition, automakers will need to change their manufacturing processes to integrate aluminum into the assembly line.
Another hurdle involves the supply of highly-engineered alloys. Bertolini said Tesla pushed the envelope with new alloys, which worked great when the company was building fewer cars. But demand for aluminum skyrocketed for the Tesla Model 3, he said. “We don’t have enough industry capability to provide this exotic material at the required tolerances,” said Bertolini. So Tesla opted for more common alloys to expand its supplier base. “That’s a challenge for the extrusion industry – to bring the tide up so more people can supply more highly-engineered products,” said Bertolini. (For more on aluminum, check out the Aluminum Extruders Council’s website at www.aec.org.)
For now, material selection is often about trade-offs, said Bertolini. OEMs want the ultimate in high strength, the closest tolerances available and the best crash performance. “I tell them to pick two,” said Bertolini. “But that’s what the customer wants, and to move forward we need to learn how to do all three and balance them properly to give the best performance for the dollar and the pound.”
It’s a challenge faced by all material suppliers. “The reality is if we don’t do it on the aluminum side, the automakers will walk over to the next guy and say, ‘What are you going to do for me?’” said Bertolini. “And if the next guy is CFRP or magnesium, then the automakers will get on that horse and ride it. The OEMs are material neutral, as long as it does what they want and it’s cost effective.”
If you’re interested in staying up-to-date on new developments in the automotive industry, then join the Automotive Composites Alliance (ACA), one of ACMA’s Composites Growth Initiative committees. The ACA represents manufacturers and material suppliers who actively promote the benefits and use of composites in the automotive industry. For more information or to join, contact Sarah Boyer at sboyer@acmanet.org or 703-682-1653.
