Making metals lighter, but stronger than steel.

• Position: INSIDESCIENCE+TECHNOLOGY

* The military truck industry relies upon iron and steel components that are hardy enough to withstand blasts on the battlefield. But the strength of such parts comes with a trade-off; the dense materials weigh down vehicles making them less maneuverable than desired.

Manufacturers for years have been seeking lighter materials that offer the same protective qualities of steel and iron. Many of them are turning to aluminum and magnesium alloys that are reinforced with small particles for strength. But these composites require expensive and complicated tooling processes to cast or machine the material into parts.

A team of researchers at the University of Wisconsin-Madison has come up with an experimental casting technique that doubles the strength of alloys by incorporating tiny ceramic particles into the molten metals, or melts. The new manufacturing process could open the doors for commercial-scale production of metal matrix nanocomposite components in the coming decade.

Nanoparticles are widely used in polymers and plastics, but are rarely mixed in with metals from a casting standpoint. When added to molten metals, nanoparticles tend to clump together. Dispersing them evenly throughout the mixture strengthens the cast metal. But it is difficult to separate the particles, which are smaller than blood cells.

"One of the biggest problems in the nanotechnology field is dispersion of the nanoparticles," says Xiaochun Li, a materials engineering professor at the university.

He and his team discovered that employing high-intensity ultrasonic waves--a process called cavitation--inside the molten metal solves that problem. The sound waves generate bubbles that expand and contract rapidly at 20,000 cycles per second. Eventually they burst, and create a huge shock wave, says Li, the lead investigator. The energy generated by that "micro nuclear bomb" is enough to disperse nanoparticle clusters evenly within the melt, he adds. So far, the team has been able to produce two-pound ingots.

The National Institute of Standards and Technology in January awarded $10.1 million to the team to continue the research. Wisconsin-based companies including aluminum casting specialist Eck Industries Inc., truck manufacturer Oshkosh Corp. and Houston, Texas-based Nanostructured & Amorphous Materials Inc. are contributing resources to the five-year project. The goal is to achieve mass production of lightweight, strong-performance aluminum and magnesium nanocomposites.

...