Understanding Magnesium Corrosion Mechanisms

Magnesium has low density and high strength which makes it very useful for lightweight applications in the automotive and aerospace industries. However, it has a high rate of corrosion, which hinders its widespread use.

Anodic hydrogen evolution enhances the rate of corrosion of magnesium at anodic potentials which cannot be predicted by Faraday's laws. Poorwa Gore, a researcher at IITB-Monash Research Academy, is therefore attempting to establish the dependence of anodic hydrogen evolution rates on the alloyed noble elements. She is working on a research project titled, 'Electrochemical corrosion of magnesium alloyed with noble alloying elements' under the supervision of Prof V S Raja and Prof Nick Birbilis.

Established in 2008, the IITB-Monash Research Academy is an important collaboration between Australia and India. It offers graduate research scholars the opportunity to study for a dually-badged PhD from both IIT Bombay in India and Monash University in Australia, spending time in both countries over the course of their research.

"Anodic hydrogen evolution is a peculiar phenomenon present in magnesium", explains Poorwa, "where hydrogen evolution reaction—which is a cathodic reaction—continues to occur on the magnesium anode and in fact the rate of hydrogen evolution goes on increasing with an increase in applied anodic potential. This is counterintuitive to conventional wisdom. The dependence of the hydrogen evolution rates on the alloying elements is important from the fundamental point of view in understanding the mechanisms of corrosion of magnesium."

This has implications not only on structural applications of magnesium and its alloys but also in other areas of magnesium usage like batteries to sacrificial anodes and hydrogen storage. Many different theories have been proposed to explain this phenomenon. In recent years techniques like in-situ ICP-MS along with polarisation have been used to study it. Besides, advanced characterisation methods like particle-induced X-ray spectroscopy have been used to characterise the corrosion films formed on magnesium to get insights into the mechanism of this so-called anodic hydrogen evolution.

Poorwa is confident that the correlation of rate hydrogen evolution with the alloying element during anodic polarization will definitely help in the design of more corrosion-resistant magnesium alloys. "In addition, she says, "understanding the rate of anodic hydrogen evolution during anodic dissolution of magnesium is key to extensive use of Mg and its alloys which is at the moment being hindered by high corrosion rates." Hence the research outcomes of this project will assist in understanding the basic mechanisms of magnesium corrosion which, in turn, will help design magnesium alloys useful in corrosive environments."

Fig. 1 : Some applications of magnesium and its alloys in the aviation and automotive sectors

Says Prof Murali Sastry, CEO, IITB-Monash Research Academy, "The research being carried out at the Academy is along thematic lines. This was a deliberate choice. The research themes represent key national research priorities of both India and Australia. We must address important research questions in areas such as Clean Energy, Water, and Infrastructure development which are vital for progress in both countries."

In trying to explain the value of her work, Poorwa adds, "If we understand magnesium corrosion mechanisms, it opens vistas for designing new alloys which can be used in structural applications in the aerospace and automotive sectors, batteries, bio-implants, or as sacrificial anodes. This project excited me because we are trying to understand a very fundamental aspect of magnesium corrosion and the outcomes could have far-reaching implications."

Research scholar: Poorwa Gore, IITB-Monash Research Academy

Project title: Electrochemical corrosion of magnesium alloyed with noble alloying elements

Supervisors: Prof V S Raja and Prof Nick Birbilis

Contact details: poorwagore@gmail.com

This story was written by Mr Krishna Warrier based on inputs from the research student and IITB-Monash Research Academy. Copyright IITB-Monash Research Academy.