Rust-proof ultra-light alloy could open door to new engineering possibilities Monday, 30 November 2015

Australian researchers have worked together and discovered a rust-proof ultra-light magnesium-lithium alloy which could lead to new engineering applications, improve fuel efficiency, and greatly reduce global greenhouse gas emissions.

The researchers, from the UNSW School of Materials Science and Engineering and Melbourne's Monash University, found that the magnesium-lithium alloy not only displays high strength, and weighs half as much as aluminium and is 30% lighter than magnesium, but is also effectively rust-proof. These properties make it an attractive candidate to replace commonly used metals in transport applications.

The alloy effectively protects itself from corrosion and rust, by forming a protective layer of carbonate-rich film on its surface upon exposure to air.

According to Professor Michael Ferry from UNSW’s School of Materials Science and Engineering, the researchers found the corrosion-resistant properties of the alloy by chance, when the team noticed a heat-treated sample of magnesium-lithium alloy from Chinese aluminium-production giant, CHALCO, sitting inert in a beaker of water in their laboratory.

"This is the first magnesium-lithium alloy to stop corrosion from irreversibly eating into the alloy, as the balance of elements interacts with ambient air to form a surface layer which, even if scraped off repeatedly, rapidly reforms to create reliable and durable protection," Professor Ferry said.

To confirm the formation of the protective surface film, the UNSW team partnered with scientists on the Powder Diffraction (PD) beamline at the Australian Synchrotron. The research found that the alloy contains a unique nanostructure that enables the formation of the protective film.

The researchers also compared the surface condition of two samples of the magnesium-lithium alloy after immersing them for 20 hours in salt water. The first sample was a non-processed alloy, while the second was first heat-treated and water quenched. The surface of the processed alloy was found to have remained in near pristine condition, when examined under an optical profilometer.

The researchers are now investigating the molecular composition of the underlying alloy and the carbonate-rich surface film, seeking to understand how this alloy impedes the corrosion process.

Professor Nick Birbilis, School of Materials Science and Engineering at Monash University, says viewing unprecedented structural detail of the alloy through the Australian Synchrotron will enable the team, involving researchers from Monash University, CHALCO, and Nanjing University of Technology in China, to work toward commercialising the new metal.

"We’re aiming to take the knowledge gleaned at the Australian Synchrotron to incorporate new techniques into the mass-production of this unique alloy in sheets of varying thickness, in a standard processing plant," Professor Birbilis said.

“These panels will make many vehicles and consumer products much lighter and, eventually, just as durable as today’s corrosion-resistant stainless steel, another example of how advanced manufacturing is unlocking the potential of materials that have been under investigation, in too narrow a manner, for centuries.”