Corrosion Behavior of Zn-Al, Zn-Mg, and Zn-Mg-Al Coatings in Simulated Concrete Pore Solution

The corrosion behavior of Zn-0.2% Al, Zn-0.5% Mg, and Zn-0.5% Mg-0.2% Al coatings in simulated concrete pore solution was studied by energy dispersive spectrometry (EDS), scanning electron microscopy, x-ray photoelectron spectroscopy (XPS), and potentiodynamic polarization tests. Results showed that the addition of alloying elements Al and/or Mg in the zinc-based coating was beneficial to suppress the anodic reactivity of zinc-based coatings when compared with the conventional Zn coating in the early corrosion process. This was mainly related to the physical barrier effect of the oxide layer on the outermost layer of the Zn-Al, Zn-Mg, and Zn-Mg-Al coatings. However, with increasing immersion time, the Zn-Al coating presented lower corrosion resistance than that of the conventional Zn coating, while the Zn-Mg and Zn-Mg-Al coatings presented higher corrosion resistance compared to the conventional Zn coating. EDS and XPS analysis indicated that the presence of alloying Mg led to the formation of Mg-rich protective layer on the Zn-Mg and Zn-Mg-Al coatings, which resulted in the improved corrosion resistance of the Zn-Mg and Zn-Mg-Al coatings in the simulated concrete pore solution.