A very light metal with a corrosion problem
Magnesium has long attracted engineers for its low weight, but it corrodes easily. That is the gap the Monash University work towards stainless magnesium set out to narrow. It focuses on corrosion control in a magnesium alloy, which, if solved, could widen the use of these materials in industries such as the automotive sector. Magnesium is the lightest of the common structural metals, and precipitation-hardened magnesium alloys have a strength-to-weight ratio comparable to strong aluminium alloys. It is about a third lighter than aluminium and roughly three quarters lighter than steel, so it suits applications that require low weight. However, because it corrodes easily, magnesium is used less than its low weight would suggest. Cathodic poisoning, a technique already known in other alloy systems, is the strategy the Monash team applied to magnesium to reduce its corrosion.The key is slowing the corrosion
The researchers found that adding about a third of a percent of arsenic to the alloy made it corrode almost ten times more slowly in tests in a salt solution. Cathodic poisons slow the hydrogen-producing half of the corrosion reaction, which reduces the free hydrogen gas that the corrosive reaction needs. The study was a first demonstration of the principle, and Monash described it as a step towards stainless magnesium rather than the finished material. Magnesium weighs roughly a quarter as much as steel, so a version that corroded far less could be useful in some automotive applications. Monash argued that a more corrosion-resistant magnesium would allow wider use in transport, with savings in weight and energy. Corrosion in these alloys depends strongly on their chemical makeup. The presence of elements such as iron, nickel, copper, and cobalt promotes corrosion at active sites in the alloy, and the effect of iron can be offset by adding manganese. Arsenic works differently: as a cathodic poison it slows the corrosion reaction instead of stopping it.Who did the work and what has happened since
The Monash team was led by Nick Birbilis, then an Associate Professor in the Monash Department of Materials Engineering. Earlier research had already eased other weak points of magnesium alloys: high-temperature creep (slow deformation under heat and load) with rare-earth additions such as gadolinium, and flammability with a little calcium. Corrosion had improved far less. In this work the team added small amounts of arsenic, a cathodic poison, to a standard magnesium structural alloy. In 2013, Birbilis said the arsenic effect was being trialled as an additive to existing commercial alloys, and New Atlas reported that his lab was working with corporate sponsors on commercially practical versions. We have not found a later public report of a commercial product. The results were published in 2013 in the journal Electrochemistry Communications, and were announced on Monash University’s official webpage. The research was carried out with Swansea University in Wales and CSIRO. This is a laboratory result on slowing the corrosion of magnesium alloys, not an engine or a vehicle prototype. If more corrosion-resistant magnesium does reach vehicles, the expected gain is weight and energy savings in transport, as Monash pointed out.First published on September 3, 2024. Corrected on October 28, 2026 to remove inaccurate statements: the research is a 2013 magnesium alloy study, not an engine.
