Study shows nano-architectured aluminum has steely strength

A North Carolina State University researcher and colleagues have figured out a way to make an aluminum alloy, or a mixture of aluminum and other elements, just as strong as steel.

That’s important, says Dr. Yuntian Zhu, professor of materials science and the NC State researcher involved in the project, because the search for ever lighter — yet stronger — materials is crucial to devising everything from more fuel-efficient cars to safer airplanes.

In a paper published in the journal Nature Communications, Zhu and his colleagues describe the new nanoscale architecture within aluminum alloys that have unprecedented strength but also reasonable plasticity to stretch and not break under stress. Perhaps even more importantly, the technique of creating these nanostructures can be used on many different types of metals.

Zhu says the aluminum alloys have unique structural elements that, when combined to form a hierarchical structure at several nanoscale levels, make them super-strong and ductile.

The aluminum alloys have small building blocks, called “grains,” that are thousands of times smaller than the width of a human hair. Each grain is a tiny crystal less than 100 nanometers in size. Bigger is not better in materials, Zhu says, as smaller grains result in stronger materials.

Zhu also says the aluminum alloys have a number of different types of crystal “defects.” Nanocrystals with defects are stronger than perfect crystals.

Now, Zhu plans on working on strengthening magnesium, a metal that is even lighter than aluminum. He’s collaborating with the Department of Defense on a project to make magnesium alloys strong enough to be used as body armor for soldiers.

Zhu’s colleagues on the Nature Communications paper are affiliated with the University of Sydney in Australia; the University of California, Davis; and Ufa State Aviation Technical University in Russia.

The Department of Materials Science and Engineering is part of NC State’s College of Engineering.

Note: An abstract of the paper follows.

“Nanostructural hierarchy increases the strength of aluminium alloys”

Authors: Yuntian Zhu, North Carolina State University; Peter Liddicoat, Simon P. Ringer and Xiao-Zhou Liao, University of Sydney; Yonghao Zhao and Enrique J. Lavernia, University of California, Davis; Maxim Y. Murashkin and Rusian Z. Valiev, Ufa State Aviation Technical University

Published: Sept. 7, 2010, in Nature Communications

Abstract: Increasing the strength of metallic alloys while maintaining formability is an interesting challenge for enabling new generations of lightweight structures and technologies. In this paper, we engineer aluminium alloys to contain a hierarchy of nanostructures and possess mechanical properties that expand known performance boundaries — an aerospace-grade 7075 alloy exhibits a yield strength and uniform elongation approaching 1 GPa and 5%, respectively. The nanostructural architecture was observed using novel high-resolution microscopy techniques and comprises a solid solution, free of precipitation, featuring (i) a high density of dislocations, (ii) subnanometre intragranular solute clusters, (iii) two geometries of nanometre-scale intergranular solute structures and (iv) grain sizes tens of nanometres in diameter. Our results demonstrate that this novel architecture offers a design pathway towards a new generation of super-strong materials with new regimes of property-performance space.

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