https://phys.org/news/2023-02-counterin ... lloys.html
by Kelly Oakes, Norwegian University of Science and Technology
Humans have been mixing metals to create more useful materials for thousands of years. The Bronze Age, which started around 3300 BC, was characterized by the use of bronze, an alloy of copper and tin which is stronger than either metal alone.
Now, researchers at NTNU have discovered a counterintuitive way to make a much more recent invention—nanograined alloys, featuring nano-sized grains of the alloying element—even stronger.
Aluminum is a metal that is widely used to make components in the aerospace, transport, and construction industries, in part because it is lightweight yet durable. Alloys of aluminum retain these qualities but are stronger than aluminum alone.
"If it was a pure aluminum, of course, it's not strong enough," says Yanjun Li, Professor of Physical Metallurgy in the Department of Materials Science and Engineering at NTNU.
Large particles decrease strength
But in recent years, researchers attempting to make nanograined alloys of aluminum containing copper have run into a problem: the copper atoms have a tendency to clump together, forming coarse particles with aluminum inside the material, especially at temperatures higher than 100°C.
When the copper is no longer evenly distributed throughout the material, the alloy becomes weaker.