Effect of Pulse Frequency on Performance of Electroplated Nanocrystalline Ni-Fe Alloy Coatings

Nanocrystalline Ni-Fe alloy coatings were prepared on Cu-Zn alloy substrate by pulse electroplating.The morphology of as-prepared Ni-Fe alloy coatings was observed using a scanning electron microscope,and the grain size of the alloy coatings was analyzed by means of X-ray diffraction.Moreover,the anodic polarization curves and electrochemical impedance spectra of the alloy coatings in 3.5% NaCl solution were measured with an electrochemical work station so as to evaluate their corrosion resistance.It was found that Ni-Fe alloy coatings obtained under different pulse frequencies were uniform and compact.With the increase of pulse frequency from 0.5 kHz to 3.5 kHz,the Fe content of the coatings varied nonlinearly between 14.17% and 22.77%,and the grain size decreased gradually from 23 nm to 15 nm.In the meantime,the corrosion resistance of the alloy coatings tended to vary in a notch-like mode,and the alloy coatings obtained at pulse frequencies of 1.5~2.5 kHz showed good corrosion resistance.Particularly,Ni-Fe alloy coating prepared at a pulse frequency of 1.5 kHz exhibited the best corrosion resistance,with a corrosion current density of about 0.216 μA/cm2 and polarization resistance of about 1.443×105 Ω·cm2.