Aluminum that’s as strong as steel

UC DAVIS (US) — An aluminum alloy of unprecedented strength can be made using a new technique that involves high-pressure twisting.

The aluminum alloy has a strength of one gigapascal, a quality usually only found in very heavy steel, says Enrique Lavernia, distinguished professor of chemical engineering and materials science at the University of California, Davis.

“Normal aluminum has only a percentage of that strength,” he says.

Details about the work were reported this month in the journal Nature Communications.

Engineers have known for some time that nanostructured metals, those with a very small grain size, are very strong, Lavernia says. But at the same time, these metals lose ductility—meaning that they can absorb less energy before breaking.

UC Davis researchers had previously pioneered materials with grain sizes at multiple scales, which combine both strength and ductility, Lavernia says.

In the new study, researchers treated aluminum 7075—a widely used alloy of aluminum that contains 2 percent zinc and magnesium—to create even smaller clusters of atoms within grains and at grain boundaries.

“Think of a hierarchy of length scales, from atomic clusters to grains of different sizes,” Lavernia says.

The researchers subjected the alloy to a high-pressure twisting step and a natural aging treatment, then studied the fine structure of the treated alloy. They found nanometer-sized grains and, concentrated within those grains and at grain boundaries, clusters of zinc and magnesium atoms.

The material was about twice as strong as conventional aluminum alloys while retaining ductility.

“By combining information on grain orientation and solute (zinc) arrangement, we can engineer materials of great strength,” Lavernia says.

Other collaborators include researchers from the University of Sydney, North Carolina State University, and Ufa State Technical Aviation University in Russia.

The work was supported by the Australian Research Council, the U.S. Department of Energy and the U.S. Office of Naval Research.

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