Surface characterization, mechanical properties and corrosion behaviour of ternary based Zn-ZnO-SiO₂composite coating of mild steel

Zinc coatings are obtained either from cyanide, non-cyanide alkaline or acid solutions. Because of the pollution and high cost associated with cyanide, deposition from other baths is gaining importance. In order to develop a bath with additive that could produce a quality coating is the motivation behind this present work which is surface modification of Zn-8ZnO-SiO₂ nano composite coating on mild steel surface by electrodeposition route. The influence of SiO₂ on Zn-8ZnO sulphate electrolyte on the properties and microstructure of the produced nano-coatings were investigated. The SiO₂ was varied from 0 to 16wt%. The microstructure characteristics of these produced series composites coating were investigated using scanning electron microscopy couple with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction and atomic force microscopy (AFM). The corrosion degradation properties in 3.65% NaCl medium were studied using potentiodynamic polarization technique and characterized by high resolution optical microscope (HR-OPM). The hardness and wear of the composite coating were measured with high diamond microhardness tester and dry abrasive MTR-300 testers respectively. The results showed that average hardness value of 142.5 and 251.2HV and corrosion rate of 0.13088 and 0.00122 mm/yr were obtained for the 0 and 16wt% SiO₂ in Zn-8ZnO. The work have established that upto 16% SiO₂ in Zn-8ZnO composite coating on mild steel can be used in improving the microhardness, wear loss and corrosion resistance of mild steel.