In the mid-19th century, aluminum was one of the most expensive metals on Earth, even though it's one of the most abundant metals in the Earth's crust. That was because of the expensive and complicated process needed to turn it from its natural state to the metal we all enjoy. In the late 1880s, that changed with the development of the Hall–Héroult process, which enabled aluminum to be cheaply manufactured and led to its widespread use in everything today from building frames to soda cans to airplanes.
As a side effect, the Hall-Héroult process also makes magnesium easy and cheap to manufacture. This has some potential manufacturing benefits as well, as magnesium is even lighter than aluminum, is also very abundant in the Earth's crust, and can be used in many similar applications - opening the door for more energy efficiency and other benefits.
The problem, though, is that magnesium is pretty soft. Its properties make it ideal for composing alloys of aluminum and other metals, but alloys composed primarily of magnesium end up being less useful for the same structural applications we use aluminum in.
Left: Pure magnesium. Right: A new magnesium/silicon carbide composite. (Credit: UCLA Scifacturing... [+]
However, a new paper from a team of researchers at UCLA indicates the potential for magnesium to be for the 21st century what aluminum was for the 20th.
One idea for improving the structural stability of soft metals like magnesium proposed by materials scientists has been to disperse silicon carbide nanoparticles in a molten metal. Then when the metal is cooled, the nanoparticles should, in theory, provide a lot more structural strength to metals, making them more useful for certain applications.
In practice, this has turned out to be more difficult. The challenge has been to get those nanoparticles to disperse uniformly within magnesium or other metal matrices, because they have a tendency to clump together. Without uniformity, you can't rely on the metal to build things like skyscrapers or airplanes.
It wasn't easy, but the UCLA team was able to successfully develop a process that achieved a uniform dispersion of silicon carbide nanoparticles into a molten magneisum-zinc alloy.
The metal was then subjected to a process called high-pressure torsion. During this procedure, the metal was compressed while undergoing torsional strain, a process that's been successfully used in recent decades to produce highly-homogeneous metals with great strength.
The result, according to the researchers, is a material that's 86% magnesium alloy and 14% silicon carbide - with some promising properties for applications. "An enhancement of strength, stiffness, plasticity and high-temperature stability is simultaneously achieved, delivering a higher specific yield strength and higher specific modulus than almost all structural metals," they wrote in their paper.
"It’s been proposed that nanoparticles could really enhance the strength of metals without damaging their plasticity, especially light metals like magnesium, but no groups have been able to disperse ceramic nanoparticles in molten metals until now," said Xiaochun Li, principal investigator on the research, said in a press release. "With an infusion of physics and materials processing, our method paves a new way to enhance the performance of many different kinds of metals by evenly infusing dense nanoparticles to enhance the performance of metals to meet energy and sustainability challenges in today’s society."
