Preliminary Corrosion Behavior of Zn-Al-Mg and GI Coatings in Typical Soil Environments

This study employed scanning electron microscopy (SEM), glow discharge spectroscopy (GDS), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and electrochemical analysis techniques to investigate the microstructural characteristics, corrosion rates, and corrosion mechanisms of Zn-Al-Mg (ZMA) coatings and pure zinc (GI) coatings before and after a 2 year corrosion test conducted at two soil testing stations located in Dagang, Tianjin, and Yingtan, Jiangxi. The results showed that after two years of soil corrosion, the corrosion rate of GI in Dagang was 1.9 times that of ZMA, while the corrosion rate of GI in Yingtan was 2.6 times that of ZMA. For both GI and ZMA coatings, the corrosion rates followed the trend: Dagang > Yingtan. The conductivity at the two sites followed the trend: Dagang > Yingtan; pH value: Dagang > Yingtan; and salt content: Dagang > Yingtan. These factors mainly influence the corrosion rate by affecting the composition of corrosion products, as different rust layer structures have varying inhibitory effects on cathodic oxygen reduction. In high-chloride environments, the anodic dissolution of MgZn 2 in ZMA coating materials releases Mg 2+ , which reacts with OH - to form magnesium hydroxide (Mg(OH) 2 ). Replacing zinc oxide with Mg(OH) 2 can reduce the cathodic oxygen reduction reaction (ORR), buffer the pH increase at cathodic sites, stabilize zinc hydroxycarbonate, and significantly enhance corrosion resistance. This makes ZMA coatings highly promising for applications in typical soil environments.