The strength of steel makes it one of the strongest materials known to man. Zinc (Zn) zinc plating makes it more resistant to corrosion. This makes it an economical choice for use in construction and infrastructure.
Over the past decade, Zn reserves have decreased markedly, forcing us to switch to Zn alloys. Magnesium (Mg) is the most commonly used mineral alloy, and when used in small amounts, it can improve the corrosion resistance of Zn.
Now Professor Myung-Hoon Lee, head of the Center for Surface Corrosion Engineering Control at Korea Maritime and Ocean University, and his colleagues have proposed a new coating for steel that promises to increase its durability. “During my time in the navy, I noticed a lot of machines that were rusting. So I did this research, hoping to produce a better anti-corrosion steel,” says Professor Li, explaining the motivation behind this research.
“In order to survive in harsh environments, it is necessary to develop materials with high anti-corrosion capacity. Steel is one such material, and increasing its lifespan makes steel more resistant,” explains Professor Lee. Their study, published in Corrosion Science, was available online on April 25, 2022, and was subsequently published in the journal’s volume 202 on July 1, 2022.
The proposed multilayer coating consists of three layers produced by physical vapor deposition (PVD). The Zn-Mg layer is sandwiched between two Zn layers. The upper Zn layer protects the Zn-Mg layer from contact with the corrosive environment. The last line of defense for steel is the underlying Zn layer.
To test the corrosion resistance of this modified steel, two samples were prepared – one containing 10% Mg and the other containing 25%. The team found that signs of rust appeared after 208 hours and 408 hours for the 10% and 25% compositions, respectively, compared to 96/120 hours for conventional Zn coatings.
Next, they compared the corrosion resistance of the two formulations. They found that the 25% compound had higher rust resistance than the 10% compound. This is contrary to previous reports suggesting that Mg content above 8% reduces the corrosion resistance of steel. Scientists attribute this contradictory finding to the presence of an upper layer of Zn, which made it possible to increase the Mg content in the Zn-Mg layer.
“The multi-layered coating on the steel makes it very stable, cost-effective and durable, making it an ideal choice for use in harsh environments,” Professor Lee concludes.
These findings can certainly have far-reaching applications in infrastructure and construction, where durable steel is an important requirement.