The battle lines have been drawn now that Ford’s ground-breaking F-150 – made with aluminum – is in full production. Speculation about the spread of aluminum into other steel-dominated platforms is rampant these days. The U.S. Department of Energy has added fuel to that debate, announcing a conditional commitment for a $259 million loan to Alcoa Inc.
If finalized, the loan would support the company’s Alcoa, Tennessee, manufacturing facility. Alcoa, the largest producer of aluminum in the United States, hopes to use the facility to produce high-strength aluminum for North American automakers looking to lightweight their vehicles.
“This is good news for Alcoa and Tennessee,” said Senator Lamar Alexander. “Today, more than one-third of Tennessee manufacturing jobs are auto related, and investment in advanced manufacturing is an important part of how our state will continue to attract good-paying jobs.”
Alcoa estimates that its expanded production will create 200 permanent full-time jobs – in addition to 400 jobs at the peak of construction. The plant’s expansion will provide additional aluminum sheet manufacturing capacity intended for the U.S. automotive market.
The goal is to boost fuel economy by reducing vehicle weight, while still maintaining safety. High volume models such as the F-150, for example are using aluminum-intensive designs to do just that. Ford’s new model features weight savings of more than 700 pounds per vehicle.
Alcoa’s Micromill system is ideally suited to making aluminum sheet with short lead times. This may be the high volume production enabler for OEMs and Tier Ones in the auto industry
Aluminum for Mercedes?
The Tennessee location of Alcoa’s new facility is quite a statement. It’s clearly not aimed at the current high-volume aluminum automotive product, the F150. That pickup is built in two plants in Dearborn, Michigan and Kansas City, Missouri (i.e. nowhere near Tennessee). The southern state, however, is not far from several major players, including Mercedes-Benz, who builds SUVs at the firm’s massive Tuscaloosa County Alabama plant.
If the F150 proves a sales success (early indications suggest so), it will be difficult to imagine that a premium automaker could resist the temptation to adopt the lightweight metal. Mercedes-Benz has yet to announce such a move. That being said, the luxury carmaker used an aluminum structure in a limited production sports car. Similarly, it has announced that the battleship weight S-Class will go on a diet using aluminum, high-strength steel and composites. Don’t be surprised if future Mercedes SUVs’ surface with a light alloy shell.
Steel fights back
The steel industry is understandably fighting back against the new interest in aluminum for mass-market automobiles. “HSLA,” High Strength Low Alloy steels, were the first to offer an alternative to aluminum by allowing down gauging of sheet stampings with no loss of strength.
However, that weight advantage came at a cost, namely some highly anisotropic (directionally dependent) physical properties. Standing and forming operations produced cracking depending on the direction in which a sheet was rolled, requiring changes in tooling and handling procedures.
Increasing strength while maintaining ductility is the classic problem of sheet steel alloys. But formability is just as important. Some HSLA steels can require up to a third more power than conventional carbon steels in stamping and forming operations.
ArcelorMittal VP Global Research Greg Ludkovsky discusses steel for auto applications
Steel has another trick up its sleeve in the fight against aluminum: tailored blanks. Typically laser welded, the concept is simple. It involves making the blank thicker where the mass is needed and thinner where it is not, reducing part weight.
It’s an expensive solution, but in most cases steels must be one third the sheet thickness of aluminum grades. This is to maintain equivalent strength with matching weight in common automotive applications.
Aluminum has formability issues as well. With up to three times the springback of a steel sheet of the same thickness, tooling commonality is impossible in many cases. Sheet aluminum also has anisotropic physical properties; many automotive grades have poor performance in deep drawing applications.
Another factor is the ever-present surface passivation layer on aluminum sheets. This thin layer of aluminum oxide is caused by reaction with air. It is extremely hard and abrasive to tooling. Surface coatings and lubricant choices are important for high-volume stamping and forming operations. Many users also report that compared to steel, aluminum stamping is very sensitive to blank geometry.
Tooling is getting more expensive for OEM’s and Tier Ones processing either material. And the engineering of blanks and rolls are more critical to high-volume close tolerance stamping and forming. With alternative fastening technologies like those recently adopted at Cadillac, massive fixtures forcing broad-flanged margins together for spot welding just do not cut it.
We’re living in an age when the lowliest Hyundai Accent has outstanding fit and finish. Can high-strength steels and aluminum coexist? In the short to medium term, the answer is yes. But when the light alloy shows up in the most conservative of auto segments (light trucks), the battle between steel and aluminum will get even more interesting.