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Aluminum

Aluminum’s evolution

By Gretchen Salois

Honing in on the pros and cons of aluminum lithium alloys in high-tech applications

June 2013 - Technological advancements place bigger expectations on materials used for the aerospace industry. Composite materials are popular, but newer alloys are being used, also. Metallurgists continue to fine tune alloys, and aluminum lithium alloys are being increasingly used to provide strength, as well as versatility. Those working with these advanced alloys can speak to the benefits and learning curves presented when working with the metal.

Adding lithium to aluminum alloys decreases the density and increases structural strength and increases corrosion resistance. Use of aluminum lithium alloys has increased due in part to use on space shuttle fuel tanks and for commercial aircraft. “Experience [working] with these applications has increased the body of knowledge regarding processing and performance characteristics,” says Don Graham, manager, education and technical services at Seco Tools Inc., Troy, Mich. “This in turn leads to an increased comfort level with the material and increased consumption.”

The use of these alloys grows every day, says Kevin Lowery, director of corporate communications, Alcoa Inc., Pittsburgh, which produces the alloy. The aluminum producer is in the process of finalizing its expansion in the U.K. and has broken ground on a greenfield aluminum lithium facility adjacent to its Indiana facility in Lafayette. “Based on feedback from customers in the aerospace market, we’ve launched these expansion efforts,” he says. “We developed the alloys and took it to the OEMs in the aerospace market. They wanted it and they wanted more than we were able to produce so we had to increase capacity in three areas.”

Easier to handle

One of the best-known characteristics associated with these alloys is resistance to high fatigue. “In applications where the loads imposed during use vary with time, reliability and resilience are high,” he says. “Crack initiation and propagation is hindered.” The newer alloys on the market are more easily welded.

Having worked with previous generations, Graham finds those alloys more abrasive than more traditional aluminum alloys. “This results in increased abrasive wear of the cutting edge,” he says. “To combat this and improve tool life, hard coatings and hard cutting edges are used.” Commonly, diamond-like carbon and chemical vapor deposition diamond coatings are commonly used. Polycrystalline diamond tools are even more common, he adds. 

Aluminum lithium alloys are challenging popular composites and Alcoa’s third-generation aluminum lithium alloys don’t require the industry to completely retool. Alcoa released its third-generation aluminum lithium alloys two years ago. “Some of the older versions of the aluminum presented challenges in terms of corrosion; there were also issues with what it looked like,” Lowery explains. “The third generation has enhanced corrosion resistance, so much so that when we show people a sheet of it, they often think it’s been polished.”

Although aluminum lithium alloys are primarily used for the aerospace industry, and as a means to reduce the weight of defense systems and weaponry, Lowery says there is potential for their use in other markets. “If someone knocks on our door and wants this alloy for some different use, part of our job at Alcoa is to find the right thing for the right application,” he says. “If people are insistent, we’re ready to work on it.” 

Lowery says the third-generation alloys are dramatically different than previous generations and don’t require any real special fabrication approaches. “It’s very simple to work with,” he says. MM

 

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