Making aluminum more formable

The biggest obstacle most automakers and suppliers face in substituting aluminum for steel is the cost. By volume, aluminum is about three times more costly than steel, so while producers are using more of the lighter metal every year, they’re applying it strategically, saving it to shave off the most weight where it matters most to boost fuel economy.

The second obstacle, however, has been equally prohibitive – aluminum is a much more difficult metal to bend. In stamping presses, it can’t always handle the deep draws that are no problem for steel parts. Where steel bends and stretches, aluminum may tear. Engineers have been able to get around this problem by redesigning aluminum-intensive parts, limiting complex geometries and cool exterior shapes, saving those sorts of designs for steel.

J. Michael Murphy, Alcoa Inc.’s vice president of commercial global automotive, says producers are well aware of the formability gap between the two metals, and Alcoa has a solution that is closing some of the distance.

“Alcoa has achieved some significant breakthroughs in the past year, especially in processes which are more-formable aluminum, with some really big gains in terms of scale,” Murphy says. He adds that the company’s Micromill technology “isn’t exactly new, but it’s advanced to the point where we’re seeing groundbreaking improvements in formability and strength.”
 

Easier to bend

Anyone who has wrapped the uneaten half of a sandwich in foil knows that some types of aluminum are simple to form into complex shapes. It’s only when the metal gets thick enough to work as a structure or offer protection in a crash that it gets problematic. So Murphy says Alcoa looked to thin-gauge aluminum producers for formability inspiration.

“The roll-casting system we’re talking about isn’t exactly a new idea. It’s what has been used for disposable pie pans and foil. The problem was that those are slow processes, and the alloys are very sensitive,” Murphy says.

Applying the company’s 125-plus years of metallurgy experience, Alcoa engineers adapted thin-gauge processes into the Micromill technology, boosting the strength of aluminum sheets by 30% and increasing formability by 40%. Both of those improvements should make the metal a more-attractive option to manufacturers, Murphy says. The increase in strength means companies can shrink parts and reach the same safety and durability targets, while the formability will make aluminum viable for some of the complex shapes previously reserved for steel.

The improvements don’t erase the differences between the two metals. Steel still has a formability edge compared to Alcoa’s new sheets, and the commodity price of aluminum is still much higher than that of steel. But narrowing the gap can make Alcoa’s materials viable in applications that had been limited to only steel.

“We’re closing that gap. We’ve still got a long way to go, but the combination of weight improvements and formability puts us on the radar for a lot of components,” Murphy says. “The opportunity for us is to make the pie bigger, to expand the applications where you can use aluminum.”
 

Roll-casting technology, opportunities

Most of the aluminum sheet sold today comes from a lengthy, capital-intensive process called direct-chill casting, Murphy states. Metals companies pour molten aluminum into ingot molds and let it harden. The ingots then get heated to a specific temperature and rolled into very thick sheets. Those thick sheets cool, get reheated, and then get rolled into thinner gauges. Producers repeat the heat, roll, cool process multiple times until the sheets are thin enough to send to automakers. Typically, that process requires 20 days to go from initial metal creation to final sheet.

Alcoa’s Micromill process, on the other hand, requires roughly 20 minutes to go from molten metal to sheet. Murphy says the company pours the molten metal onto a system that cools it and rolls it into thin gauges in one pass, eliminating the multiple heat-roll-cool steps. More important, the quick-cooling system results in a microstructure that can bend further without tearing, making it suitable for deeper die draws.

“It’s creating products unlike any that our customers have ever seen,” Murphy says.

Another benefit is a smaller footprint. Micromills take up about 25% of the space of a traditional mill. Alcoa has a pilot facility in San Antonio, Texas, that it is using to make test materials and show off its capabilities. As customers study the system and start placing metal orders, Murphy says that expanding capacity by adding Micromill equipment to other plants would be worth considering.

The 2025 federal fuel economy mandate of 54.5mpg has automakers willing to consider lightweight metals more than ever before, and aluminum made huge inroads in 2014, most notably making up the entire vehicle body of Ford’s F-150 pickup. Higher costs and limited formability have discouraged automakers from adopting the material en masse, Murphy says. But the landscape is shifting toward aluminum.

“I’d love to see every steel part get replaced by aluminum, but we’re more likely to see more multi-metal cars,” Murphy says. “The discussion in the industry has shifted from everyone wanting to use one process or material.”

He adds that aluminum won’t always be the metal of choice for components. In some cases, more exotic materials such as magnesium and carbon fiber might offer even greater weight savings. In others, steel will be suitable, keeping costs down. Alcoa’s goal with Micromill is to have a shot at competing as often as possible.

“Last year was a fun year for us with the launch of the Ford F-150. You only get an opportunity like this – this massive shift from steel to aluminum – once in a lifetime,” Murphy explains. “Now, it’s about fighting for every part, and we think we’ve got a good shot at winning.”

Alcoa Inc.
www.alcoa.com

About the author: Robert Schoenberger is the editor of TMV and can be reached at 216.393.0271 or rschoenberger@gie.net.