Corrosion resistance of Zn-Ni coatings containing ZrO2 nanoparticles

Corrosion resistance of Zn-Ni-ZrO2 nanocomposite coatings was studied. Zn-Ni alloy was electrodeposited on mild steel substrate from an alkaline bath used by galvanic industry (Atotech). ZnNi-ZrO2 nanocomposite coatings were obtained by adding to the deposition bath 10 g L-1 of yttria stabilized ZrO2 nanoparticles (Aldrich, particle size < 100 nm, 10.14 wt% Y2O3). Electrodepositions were carried out at 25±1 °C under constant magnetic stirring and under galvanostatic control (current density: 30 mA cm-2). Homogeneous and compact coatings with low grain size have been obtained. All the electrodeposited alloys are constituted by cubic γ phase Ni5Zn21; the incorporation of ZrO2 nanoparticles does not change the orientation of γ phase. The ZrO2 content of the coatings was 1.2 wt%; the incorporation of zirconia nanoparticles does not lead to a change in the morphology. Corrosion resistance of both Zn-Ni and Zn-Ni-ZrO2 coatings was studied by means of polarization resistance measurements, potentiodynamic polarizations and electrochemical impedance spectroscopy performed at room temperature in 3.5 % NaCl solution. The obtained results indicate that, under the experimental conditions of this work, ZrO2 incorporation leads to a slight improvement in corrosion resistance of Zn-Ni alloy. EIS measurements, performed at different immersion times, show an increase in corrosion resistance with the time, due to the formation of a uniform and compact layer of Zn5(OH)8Cl2.