US researchers produce ultra-strong aluminum alloys for additive manufacturing

A team at Purdue University have developed a patent-pending process to create ultra-high-strength aluminum alloys that are suitable for additive manufacturing due to their plastic deformability.

The team, led by Haiyan Wang and Xinghang Zhang, both professors at Purdue University’s School of Materials Engineering, introduced transition metals such as cobalt, iron, nickel and titanium into aluminum. These metals were integrated into the aluminum using nanoscale, lamellar and deformable intermetallic compounds. This new method makes it possible to develop ultra-strong and at the same time highly formable aluminum alloys that are particularly suitable for use in 3D printing. Anyu Shang, a materials science graduate, completes the team.

“Our work shows that the proper introduction of heterogenous microstructures and nanoscale medium-entropy intermetallics offers an alternative solution to design ultrastrong, deformable aluminum alloys via additive manufacturing,” Xinghang Zhang said. “These alloys improve upon traditional ones that are either ultrastrong or highly deformable, but not both.”

The innovation was reported to the Purdue Innovates Office of Technology Commercialization, which has applied for a patent from the US Patent and Trademark Office to protect the intellectual property. The research results were published in the journal Nature Communications. The work was supported by the National Science Foundation and the US Office of Naval Research.

Lightweight, high-strength aluminum alloys are used in industries such as aerospace and automotive. However, most commercially available high-strength aluminum alloys are unsuitable for additive manufacturing because they are susceptible to hot cracking, which can lead to material defects. A traditional method of avoiding hot cracking is to introduce particles that impede the movement of dislocations and thus increase strength. However, these alloys usually only achieve a strength of 300 to 500 megapascals, while steels typically reach 600 to 1,000 megapascals.

Researchers at Purdue University have succeeded in producing intermetallically reinforced additive aluminum alloys by using transition metals such as cobalt, iron, nickel and titanium.

“These intermetallics have crystal structures with low symmetry and are known to be brittle at room temperature,” Shang said. “But our method forms the transitional metal elements into colonies of nanoscale, intermetallics lamellae that aggregate into fine rosettes. The nanolaminated rosettes can largely suppress the brittle nature of intermetallics.”

Wang said, “Also, the heterogeneous microstructures contain hard nanoscale intermetallics and a coarse-grain aluminum matrix, which induces significant back stress that can improve the work hardening ability of metallic materials. Additive manufacturing using a laser can enable rapid melting and quenching and thus introduce nanoscale intermetallics and their nanolaminates.”

The research team carried out macroscopic compression tests as well as micro-column tests and post-deformation analyses on the developed aluminum alloys. The macroscopic tests showed a combination of pronounced plastic deformability and high strength of more than 900 megapascals. The micro-column tests showed significant back stresses in all areas, with certain areas reaching yield stresses of over one gigapascal.

These new findings and methods for producing ultra-high strength aluminium alloys could revolutionize additive manufacturing and open up new possibilities for the use of these materials in various industries.