Corrosion resistance of Zn-Ni-Al2O3 nanocomposite coatings

Corrosion resistance of Zn-Ni-Al2O3 nanocomposite coatings was studied. Zn-Ni alloy was electrodeposited on mild steel substrate from an alkaline bath used by galvanic industry (Atotech). ZnNi-Al2O3 nanocomposite coatings were obtained by adding to the deposition bath 10 g L-1 of Al2O3 nanoparticles (delta-alumina, primary particle size: 13 nm). Electrodepositions were carried out at 25±1 °C under constant magnetic stirring and under galvanostatic control (current density: 10 and 30 mA cm-2). Homogeneous and compact coatings with low grain size have been obtained. All the electrodeposited alloys are constituted by cubic gamma-phase Ni5Zn21; the incorporation of Al2O3 nanoparticles does not change the orientation of gamma-phase. The Al2O3 content of the coatings was 1.1-1.6 wt%; the incorporation of allumina nanoparticles does not lead to a significant worsening in the morphology; only a slight increase in roughness was observed. Corrosion resistance of both Zn-Ni and Zn-Ni-Al2O3 coatings was studied by means of polarization resistance measurements and potentiodynamic polarizations performed at room temperature in 3.5 % NaCl solution. The obtained results indicate that, under the experimental conditions of this work, Al2O3 incorporation does not lead to a worsenig of corrosion resistance of ZnNi alloy because it does not significantly affect the coating morphology and structure.