Electrochemical behavior and electro-crystallization mechanism of Cu-Ni/Nano-Al2O3 coating with a deposition current density dependence

Abstract

In this work, preparation of Cu-Ni/Nano-Al2O3 composite coating with (111)-preferred orientation on the surface of the H64 brass via electrodeposition technique. Variation of the deposition current density was found to play a key role in the control of the microstructure and strongly influence the corrosion resistance of the composite coating. Electrochemical impedance spectroscopy results indicated that the increase of nano-alumina content in composite coating is caused by the change of polarization mode. Under different current densities, the Ni (111) plane is only preferred orientation and the relative texture coefficient reaches the highest value of 54.36% at 5 A•dm−2. The crystallite size of these coatings is about 10–55 nm dependent on current density, and high current density could refine the size. The microstructure of the coating changed from cauliflower to spherical with increasing deposition current density. Moreover, the Cu-Ni/Nano-Al2O3 composite coating obtained at 5 A•dm−2 increased the polarization resistance and coating resistance of the H64 brass by about 50% and 83%, respectively. The corrosion potential (Ecorr) of Cu-Ni/Nano-Al2O3 composite coating is shifted towards the nobler direction from − 1.191 V to − 0.063 V(Ag/AgCl) with the current density increases. The corrosion mechanism of Cu-Ni/Nano-Al2O3 composite coating has gone through two stages corresponding to two-time and three-time constant of EEC models, respectively. The Cu-Ni/Nano-Al2O3 has large potential merits in field of corrosion.