Improved Uniformity Properties and Corrosion Resistance of Zinc–Nickel Composite Coating Enhanced by Nano-SiO2

In this study, pre-treated low-carbon steel substrates were electroplated with Zinc–Nickel (ZN) alloy composite coatings enhanced by the incorporation of nano-silicon dioxide (SiO2) particles in an alkaline solution. ZN deposits with varying concentrations of nano-SiO2—specifically, 1, 2, 3, 5, and 10 wt%—were achieved by adjusting the ratio between the nano-SiO2 and ZN alloy electroplating solutions. The influence of the nano-SiO2 content on both the quality of the coating and its corrosion behavior was investigated in detail. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and an atomic force microscope (AFM) were utilized to assess the surface, cross-section structure, elemental composition, and thickness of the coatings. Notably, the addition of nano-SiO2 improved the microstructure of the coating, leading to a reduction in grain size as well as enhancements in uniformity and density while revealing that co-deposition reached an optimal concentration at 3 wt% nano-SiO2. The corrosion behavior of coated specimens was evaluated through electrochemical impedance spectroscopy (EIS) and polarization techniques within a 3.5 wt% NaCl solution serving as a corrosive medium. Specifically, for typical prepared coatings, the corrosion current density decreased from 1.410 × 10−4 A·cm−2 to 5.762 × 10−6 A·cm−2, which is a remarkable reduction by one to two orders of magnitude relative to the SiO2-free coatings mentioned previously. These findings provide a straightforward approach for selecting 3 wt% nano-SiO2 as an effective additive in ZN composite coatings.