Steel is one of the strongest and most robust materials found on earth. But on its own, the durability of steel is poor. Galvanizing steel with zinc (Zn) increases its corrosion resistance, making it a sustainable and economical choice to use in construction and infrastructure.
In the last decade, however, Zn reserves have fallen appreciably—prompting many in the industry to switch to using Zn alloys. Magnesium (Mg) is among the most commonly used alloy minerals, and when used in small amounts, it can improve the corrosive resistance of Zn.
With that in mind, a group of scientists from Korea Maritime & Ocean University (Busan, South Korea) are proposing a novel multilayer coating method to increase steel’s longevity.1 The work is led by Prof. Myeong-Hoon Lee, head of the school’s Center of Surface Corrosion Control Engineering.
Motivations for the Study
“During my time in the Navy, I noticed a lot of machines that were rusting,” Lee says. “So, I engaged in this research, hoping to produce better anticorrosive steel.
“To survive in harsh environments, high anticorrosive materials need to be developed,” he adds. “Steel is one such material, and increasing its lifespan makes the steel more sustainable.”
A study by Lee and his colleagues, published in Corrosion Science, was made available online on April 25, 2022, and subsequently published in Volume 202 of the journal on July 1, 2022.
Three Fabricated Layers
The proposed multilayer coating comprises three layers fabricated using physical vapor deposition (PVD), with a Zn-Mg layer sandwiched between two Zn layers. In this arrangement, the top Zn layer protects the Zn-Mg layer from being in contact with corrosive environments. The last line of defense for the steel is the bottom Zn layer.
In the study, two samples were prepared to test the corrosion resistance of this modified steel. One contained 10% Mg, while the other had 25% Mg. The team found that the signs of rust appeared at 208 h and 408 h for the 10% and 25% compositions, respectively, as compared to 96 h and 120 h for conventional Zn coatings.
Contradictory Finding
Next, they compared the corrosion resistance of the two compositions, and they found the 25% composition as having a higher resistance to rust than the 10% one. This was contrary to previous reports, which had suggested that an Mg content higher than 8% would lower the corrosion resistance of steel.
The scientists attributed this contradictory finding to the presence of the top Zn layer, which made it possible to increase Mg content in the Zn-Mg layer.
“The multilayer coating on steel makes it highly stable, economical, and durable, making it an ideal choice for use in harsh environments,” Lee concludes.
The research team believes these findings could have far-reaching applications in infrastructure and construction, where long-lasting steel is an essential requirement.
Source: Korea Maritime & Ocean University, www.kmou.ac.kr/english/main.do.
Reference
1 “The Key is in the Coating: Multilayered Coating to Improve the Corrosion Resistance of Steel,” National Korea Maritime & Ocean University Research News, July 5, 2022, https://www.kmou.ac.kr/english/na/ntt/selectNttInfo.do?nttSn=10317037&mi=4528&currPage=1 (Aug. 16, 2022).