Electrodeposition mechanism of Ni-Al composite coating

Ni-Al composite coatings were electrodeposited from a modified Watts solution. The electrochemical behavior of the coatings was studied by means of zeta potential analysis, voltammetry and electrochemical impedance spectroscopy (EIS). It was found that the zeta potential of Al particles was -4 mV which is very close to that of Al2O3. Moreover, addition of conductive Al particles into the electrolyte shifted the polarization curve to more negative potentials and loop size of EIS curve increased. It was also demonstrated that the co-deposition behavior of Ni-Al composite coatings obeys the Guglielmi's model. The results indicate that conductive Al particles behave as the inert particles and confirm the existence of a thin aluminum oxide layer on the surface of aluminum particles.