Magnesium alloys are routinely used in automobile components, electronic appliances and sporting goods because they are lightweight. However, the materials need to be coated during processing to improve their corrosion properties, which limits the applications that they can be used in.
Morinobu Endo of Shinshu University in Nagano and colleagues may have found a solution to this problem. The researchers have found that the alloys' corrosion resistance can be improved by adding around 5wt% of short, linear, well-ordered multiwalled carbon nanotubes. And as a bonus to this "breakthrough" result, the mechanical properties improve too (25 and 11% increases in the elastic modulus and tensile strength, respectively).
Preparation
Endo and colleagues prepared their carbon nanotube-filled magnesium alloy composites using a powder-powder blending technique followed by vacuum hot pressing and extruding processes. The researchers tested the corrosion resistance of the composites by immersing them in salt water and measuring how much weight the materials lost.
The scientists found that new composites hardly lost any mass after 20 hours in the salt bath. In contrast, pristine magnesium alloys lost up to 13% of their weight.
According to the team, the corrosion properties of the alloys improve thanks to the formation of stable oxide films along the grain boundaries of magnesium. "Moreover, when the nanotubes are incorporated into the magnesium alloy, the tubes prevent the oxide layer detaching from the alloy, which further slows the formation of subsequent oxide layers," Endo told nanotechweb.org.
"We envisage that the new composites are possibly the best candidates for constructing lightweight materials for automobiles," added Endo. "We even believe that they could replace aluminium alloys and engineering plastics in commercial applications where lightweight, hardness and mechanical strength are required."
The team will now develop ways to control the thermal and electrical properties of the alloys.
The work was reported in Applied Physics Letters.