Magnesium is the lightest structural metal, a desirable trait for making vehicles when weight matters. It’s also common, making up 2.7 percent of the Earth’s crust. Unfortunately, however, it is both brittle and formed at high temperatures. A newly announced technique addresses both these problems, paving the way for lighter, and therefore more fuel-efficient cars and planes, whilst also increasing the prospect of combining the two.
Magnesium is a quarter as dense as steel. Even the same volume of aluminum is 50 percent heavier. When 90 percent of the fuel used in a car moves a vehicle, rather than its occupants, the potential savings are considerable. The automotive industry recognizes this, using magnesium for features like steering wheels that can be cast, but not for things like panels that need to be beaten into shape.
Dr Zhuoran Zeng and Profesor Nick Birbilis of Monash University, Australia, are out to change that. In Nature Communications they announced the creation of a type of magnesium that is super-formable at room temperature, even without the introduction of alloys. The product can experience strains at least eight times greater than ordinary magnesium without breaking, and all it takes is patience.
The secret lies in producing magnesium made of tiny grains. Although the grains themselves remain resistant to changing shape, if they are small enough, the structure as a whole can bend easily because they rotate relative to one another.
Conventional magnesium processing doesn’t use the super-high temperatures some metals require but still needs to be done at 200-400ºC (390-750ºF). Zeng, Birbilis, and colleagues pushed pure magnesium through a die at a range of temperatures. In the 150-400ºC (300-750ºF) range, the product was predictably brittle. However, at temperatures below 80ºC (176ºF) the grains kept their size and shape, leaving a product easy to work with at room temperature, provided the process was done slowly.
“We can even roll it to the thickness of aluminum foil and bend it 180° after rolling,” Zeng said in a statement.
Birbilis told IFLScience that slower extrusion means lower productivity, but in this case, the product was well worth the wait.
Even with magnesium’s existing drawbacks, only iron and aluminum are more widely used as structural metals, and its lightness is particularly appreciated by the aerospace industry.
Birbilis told IFLScience current airplanes rely on scarce metals, and if flying cars are to become a reality, we’ll need something that is common and light. Magnesium has a reputation for being highly flammable, but Birbilis added it’s only a problem in powdered or ribbon form. Nevertheless, the aluminum industry has done its best to encourage the view that magnesium vehicles might easily burst into flames.
Examples of the exceptional malleability of the slow-extruded magnesium. Monash University