Magnesium is hot right now. Like a supermodel from the 1990s, the element combines characteristics that are seemingly at odds: It is lightweight yet powerful, when paired with the right designer. The element is also accessible to the public, but not so much that it might be considered attention seeking. Not like ‘iron’: the Penney’s model of alloy metals.
Despite falling out of favour in the 20th century, magnesium has returned to the scene. In fact, it has been keeping materials scientists up at night for the past two decades as they all try to capitalise on its attractive properties.
Light metal
Increased understanding of materials at the nanoscale is providing much insight for those engaged in the science of making things harder, better, faster and stronger.
In the case of the chemical element magnesium, it was widely agreed that if nanoparticles could be positioned in an orderly way, this would enhance the strength of the light metal, without damaging its plasticity. Until now, however, no one could figure out how to do that.
Prof Xiaochun Li and his research team from the department of mechanical and aerospace engineering at UCLA spent 10 years attempting to demonstrate the process of nanoparticle uniform dispersion. They recently had a breakthrough in their painstaking research, the findings of which were published in a recent edition of the journal Nature.
“Theoretically we knew that if we spread the particles correctly, we could achieve really high strengths,” he says. “We learnt the hard way just how difficult and time-consuming it would prove to be.”
The research team achieved a dense uniform dispersion of silicon carbide nanoparticles (14 per cent by volume) in magnesium through nanoparticle self-stabilization in molten metal. The outcome: a material with the kind of strength, stiffness, plasticity and high-temperature stability to make Iron Man quiver in his boots.
Blueprint for material
Equally significant to this research achievement, perhaps, is the context in which it was conducted. “We were conscious throughout the process that we needed to provide a blueprint for a material that could be scaled,” says Li.
“Through the successful combination of physics and materials-processing methods, we’re confident this technology can be scaled to the point where it can replace a variety of heavier metals currently in use and pave the way for more high-performance lightweight metals. I would guess early applications are likely to happen in vehicles of all kinds – from cars to airplanes – as well as body armour for police and soldiers. But we’re likely to see this technology developing in a lot of different directions.”
One obvious industry that can always use more light, yet strong, material is electronics. “A lot of smartphones and computers already use magnesium but every computer manufacturer would benefit from the introduction of a lighter material capable of withstanding greater stress,” says Li.
Common element
Magnesium is the eighth most common element found in the Earth’s crust. It can also be mined from seawater. “It is considered an emerging material, mainly because it is lightweight,” says Li. “It is about two-thirds the density of aluminium.”
Despite its attractive girth, it hasn’t always been the alkali earth metal á la mode. Popularity ebbed and flowed in the 20th century. It was one of the chief ingredients for German aerospace construction during both the first and second World Wars.
However, high extraction costs combined with chemical properties including flammability, reaction to water and most acids, as well as having both the lowest melting and boiling points of any alkali earth metal, all contributed to its later reputation as a talented but unpredictable element.
Magnesium can now be mass-produced at a lower cost. More recently, its resurgence is in part related to the ease by which the element can be recycled when compared with polymers. It is considered a more environmentally conscious choice.
Several unsuccessful approaches have been taken to strengthen it.
“People have tried every process from heat treatment to deformation as well as cohesion with numerous composites in attempts to strengthen the metal,” says Li.
“A lot of research into alloys has also been based on the dispersion of micro- rather than nano-sized particles,” says Li. Now that magnesium and silicon carbide have shown promise, there are likely to be a number of raised eyebrows in the materials industry.
Adoption should be swift if the researchers’ claims of scalability can be substantiated. “Our mission throughout was always to provide a casting method for anyone wanting to scale production,” says Li. “So I have no doubt we will see this technology in commercial use very soon.”
