Cars and Concepts

The race to find the perfect aluminum alloy

GM will use advanced mixed-material manufacturing techniques to build the Cadillac CT6 sedan. Techniques include material joining processes such as aluminum laser welding. Photo credit: GM

KENNESAW, Ga. -- Tom Boney, who runs the automotive business for aluminum giant Novelis, sees a steady migration to the lightweight metal as fuel economy standards get tougher in the years ahead.

If he’s disappointed that Jeep didn’t choose aluminum for the entire body of the next-generation Wrangler, he doesn’t show it. If he is concerned that Chevrolet, GMC, Ram, Toyota and Nissan are sticking with steel for the majority of the metal in their big pickups, he won’t say it.

Automakers are striving to meet the government’s 54.5 mpg average fuel economy standard per fleet that is on the books for 2025. And Boney believes sooner or later all manufacturers will be forced to turn to aluminum for a greater number of body panels to reduce weight and improve fuel economy.

But he understands not every company can do what Ford did to make the switch: That is, tear up plants at a cost of nearly a billion dollars to convert from steel to aluminum manufacturing.

So, if an automaker keeps a steel body-in-white, but switches the hang-on parts -- doors, hoods and trunk lids -- to aluminum, that’s fine with Boney.

“It’s going to be a multi-material industry,” he says at Novelis’ research and technology center here on the outskirts of Atlanta. “We’re glad to be on the same stage as steel.”

I recently took a tour through the facility and saw some of the areas where Novelis researchers are working to perfect next-generation aluminum alloy sheet metal that can win more share in the coming years.

Aluminum alloy is a blend of several elements -- magnesium, copper, silicon, zinc, etc. Finding the right combination of the materials is a lot like baking.

To displace steel, aluminum faces at least two big obstacles in addition to manufacturing hurdles. In the future, aluminum has to become thinner and stronger, and it has to be more formable so that designers can shape future vehicles with deep curves.

Steel got dinged last year when Ford moved the F-150 to aluminum, but the steel industry is offering a greater variety of lightweight products. And it still has one very huge advantage: Nearly all automakers’ manufacturing systems are set up to weld steel to steel. The majority of aluminum body panels are joined with rivets and industrial adhesive, a complex and costly assembly process compared with the spot welds used to join steel.

At a giant convention in Detroit for owners of body shops and collision repair professionals, Cadillac recently showed off a sectioned body of the upcoming CT6 luxury sedan.

The CT6 is one of the first vehicles to mix steel and aluminum in the body structure to add strength for safety and lightness for fuel economy. About 65 percent of the CT6’s body-in-white is aluminum, the rest is steel, some of it new ultra high strength steel. The CT6 cutaway also shows GM’s manufacturing process.

An example of two welds, the circular dots, and a fastener, or self-piercing screw, that GM uses to combine two sheets of aluminum.

GM will use its new, patented aluminum welding process, bonding, and mechanical fasteners including self-piercing rivets and self-tapping screws.

As with the Ford F-150, many of the CT6’s body parts have been designed to be serviced. So, most accident damage, even some that is structural, can be repaired.

GM figures using aluminum in the CT6 body saved around 200 pounds. GM is expected to use this same approach for the next generation of the Chevrolet Silverado and GMC Sierra pickups.

Looking at the way the CT6 body is assembled, you can see that Novelis, its chief competitor, Alcoa, and automakers have a lot of work to do if aluminum is going to make further inroads. The method of joining the metals could be the deciding factor.

If an automaker can simply replace steel with lighter weight aluminum by changing the welding tips on the assembly line robots like GM can do with its patented multi-ring domed electrode system and use mechanical fasteners in select areas, the cost to go aluminum will be dramatically reduced.

Todd Summe, vice president of global research and development for Novelis, sees welding eventually replacing bonding and riveting.

“That’s something we are actively working on,” says Summe. “How can we fit into existing spot-welding [manufacturing technology.

“I believe in the long run the trend will be towards welding processes, both a combination of spot welding and laser welding,” he said. “The reality of where we stand today self-piercing rivets and adhesives are very robust and they are the right answer in many of the applications.”

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