Monday 29 July 2024

Purdue University material engineers have created a patent-pending process to develop ultra-high-strength aluminium alloys that are suitable for additive manufacturing because of their plastic deformability.

Haiyan Wang and Xinghang Zhang lead a team that has introduced transition metals cobalt, iron, nickel and titanium into aluminium via nanoscale, laminated, deformable intermetallics. Wang is the Basil S Turner Professor of Engineering and Zhang is a professor in Purdue's School of Materials Engineering. Anyu Shang, a materials engineering graduate student, completes the team. 

Purdue University professor Xinghang Zhang (right) and graduate research assistant Anyu Shang prepare to use a 3D printer at the Flex Lab in Discovery Park District at Purdue. Zhang and Haiyan Wang, Purdue’s Basil S Turner Professor of Engineering, have developed a method to create ultra-high-strength aluminium alloys that also demonstrate high plastic deformability. Their research has been published in Nature Communications. Image: Purdue University photo/Huan Li.

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

Wang and Zhang disclosed the innovation 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 has been published in the peer-reviewed journal Nature Communications. The National Science Foundation and the US Office of Naval Research provided support for this work.

Drawbacks of traditional aluminium alloys

Lightweight, high-strength aluminium alloys are used in industries from aerospace to car manufacturing.

"However, most commercially available high-strength aluminium alloys cannot be used in additive manufacturing," says Shang. "They are highly susceptible to hot cracking, which creates defects that could lead to the deterioration of a metal alloy."

A traditional method to alleviate hot cracking during additive manufacturing is the introduction of particles that strengthen aluminium alloys by impeding the movements of dislocations. 

"But the highest strength these alloys achieve is in the range of 300 to 500 megapascals, which is much lower than what steels can achieve, typically 600 to 1,000 megapascals," says Wang. "There has been limited success in producing high-strength aluminium alloys that also display beneficial large plastic deformability."

A patent-pending Purdue University method creates ultra-high-strength aluminium alloys that also demonstrate high plastic deformability. The innovation has practical applications in industries ranging from aerospace to car manufacturing. Image: Purdue University photo/Anyu Shang.

The Purdue method and its validation

The Purdue researchers have produced intermetallics-strengthened additive aluminium alloys by using several transition metals including cobalt, iron, nickel and titanium. Shang said these metals traditionally have been largely avoided in the manufacture of aluminium alloys. 

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

"Also, the heterogeneous microstructures contain hard nanoscale intermetallics and a coarse-grain aluminium 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 nano-laminates."

The research team has conducted macroscale compression tests, micropillar compression tests and post-deformation analysis on the Purdue-created aluminium alloys.

"During the macroscale tests, the alloys revealed a combination of prominent plastic deformability and high strength, more than 900 megapascals. The micropillar tests displayed significant back stress in all regions, and certain regions had flow stresses exceeding a gigapascal," says Shang.

"Post-deformation analyses revealed that, in addition to abundant dislocation activities in the aluminium alloy matrix, complex dislocation structures and stacking faults formed in monoclinic Al9Co2-type brittle intermetallics."