Organizational Structure and Corrosion Behavior of Electrodeposited Zn-Si₃N₄ Composite Coatings

Nine types of Zn-Si₃N₄ composite coatings were prepared on the surface of carbon steel by direct current electrodeposition. The surface morphology, composition, and crystal structure of the coatings were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The corrosion resistance of the coatings was tested by electrochemical experiments, and the microhardness of the coatings was tested by a digital microhardness tester. The results show that the introduction of Si₃N₄ nanoparticles refined the grain size of the zinc coating, and the microstructure and growth texture of the coating changed. With the increase of Si₃N₄ content, the microstructure of the composite coating first transformed from dendritic structure to approximately equiaxed polygonal crystalline structure, and finally formed an approximately spherical eutectic structure. The preferred growth direction of the composite coating gradually shifted from initially prioritizing growth along the (100) and (101) crystal planed to prioritizing growth along the (100), (101), (110), and (200) crystal planes. Zn-Si₃N₄ composite coatings had better corrosion resistance than pure zinc coating, and the composite coating containing 0.2 g/L Si₃N₄ had the best corrosion resistance. At the same time, the introduction of Si₃N₄ nanoparticles also improved the hardness of the coating.