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High-strength Al alloy for 3-D printing is moving into commercial production

By Scott Jenkins |

The first high-strength, wrought-aluminum alloy powder designed for use in additive manufacturing (3-D printing) applications is moving into commercial production. The powder was developed by HRL Laboratories (Malibu, Calif.; www.hrl.com) for use in laser powder-bed fusion 3-D printers. The company recently announced that the material has been registered by the Aluminum Association (Arlington, Va.; www.aluminum.org). The alloy material was originally described in a 2017 Nature paper.

High-strength wrought aluminum alloys in the 7000 and 2000 series have been used for decades because of their strength and low-cost alloying additives (Zn, Mg and Cu), explains HRL’s Zak Eckel. These alloys are used widely, from aircraft components and industrial equipment to sporting goods, but they have not been successfully 3-D-printed before.

The main barrier to 3-D-printing of high-strength Al alloys from metal powder is that rapid melting and solidification of the feed material in 3-D printing gives rise to suboptimal crystal structure in the metal product. Because aluminum’s coefficient of thermal expansion and other properties strain the crystal structure, cracks develop easily in the solidified aluminum.

Grain refinement in metal alloys refers to strategies to control the nucleation and growth of crystal structures with desired properties. With its Al 7A77.60L alloy, HRL has developed a targeted grain-refinement method that controls the solidification of the metal in additive manufacturing to avoid the cracking phenomenon in the end product.

“We have developed an inoculant selection method, based on matched lattices, to grow aluminum grains in a way that will generate the strength and other required properties in the product,” says HRL metallurgist Hunter Martin. By functionalizing the melt pool from which solid Al can grow when solidifying in 3-D printers, we avoid large, columnar grains, Martin explains. Using zirconium, we create many points for aluminum crystal growth to occur in the desired way.

HRL is hoping to use the commercial powder to attract strategic customers looking for the performance and cost benefits of high-strength Al-alloy systems combined with the freedom of additive manufacturing. Among the initial applications of 3-D-printed Al-alloy parts is replacement parts in aging, high-value equipment for which tooling for components no longer exists.

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