A Study of Microstructure and Electrochemical Corrosion Behavior of Coatings with Different Aluminum and Magnesium Contents

摘要

Based on the relevant literature, this paper uses a simulator to experimentally produce two types of zinc coatings in the laboratory: Zn -20%Al-5%Mg and Zn-15%Al-6%Mg. Compared with the commercially mature products Zn -11%Al- 3%Mg and Zn -6%Al-3%Mg, Zn -20%Al-5%Mg and Zn -15%Al-6%Mg coatings are analyzed. This paper employs Scanning Electron Microscopy (SEM) and electrochemical corrosion to analyze the microstructure and corrosion resistance of the four types of Zn-Al-Mg coatings. The results show that complete dendritic crystals are formed on the surface of the hot-dip Zn-Al-Mg coating, while there are no complete dendritic crystal structures in the cross -section of the coating. As the content of Al in the bath increases, the content of Zn dissolved in the Al phase g radually decreases. The mass percentages of Al and Zn on the Al dendrite formed in the four types of coating’s surface, Zn -20%Al-5%Mg, Zn -15%Al-6%Mg, Zn -11%Al-3%Mg, and Zn - 6%Al-3%Mg, they are 105%, 96.5%, 37.5%, and 22.7%, respectively. Due to the high content of Al and Mg elements in the Zn-20%Al-5%Mg coating, on the coating’s surface, the electrochemical corrosion products are a dense and insoluble film which can effectively inhibit the further occurrence of corrosion. Comparing the corrosion currents of the four coatings, the Zn-20%Al-5%Mg exhibits the best corrosion resistance.