Comparative study of zinc base alloy coatings: composition, microstructure, and corrosion resistance

The elemental composition, microstructure and corrosion resistance of three different zinc base alloy coatings (Zn-Ni alloy, Zn-Fe alloy and Zn-Co alloy) electrodeposited with the same complexing agent were studied by using a common zincate bath. The suitable current density is designed through experiments. Under the same current density, Zn-Ni alloy coating, Zn-Fe alloy coating and Zn-Co alloy coating are electrodeposited. The types and contents of microcomponent elements were analyzed by energy dispersive spectroscopy (EDS), the surface structure was analyzed by scanning electron microscopy (SEM), and the corrosion resistance was analyzed by electrochemical techniques (AC impedance, Tafel curve). The results show that the microstructure of Zn-Co and Zn-Fe alloy coatings is similar, the surface of the coatings is flat and the crystal distribution is uniform, but the grain of Zn-Co alloy coatings is obviously larger than that of Zn-Fe alloy coatings. In the electrochemical test part, the AC impedance of Zn-Co alloy coating is much higher than that of Zn-Ni alloy coating and Zn-Fe alloy coating, and the self-corrosion current density is lower than that of Zn-Ni alloy coating and Zn-Fe alloy coating, so it has the best corrosion resistance.