Effect of shaped waveform on structure and electrochemical corrosion behavior of pulse electrodeposited Ni Cu alloy coatings

Abstract

The NiCu alloy coating was electrochemically deposited from an ammonia bath on mild steel with a pulse current, of which the shaped waveform was changed into triangle, sin, ramp, and rectangular. The structural and compositional properties of the coatings were analyzed by SEM, AFM, XRD, EDS, and AAS. To investigate the corrosion resistance of the coatings, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) have been performed in aerated 3.5 wt% NaCl solution. The results provided evidence that the characteristics of the pulse-electroplated NiCu alloy coatings are influenced by the types of shaped waveform. The lowest roughness and the smallest crystallite size were obtained when the ramp waveform in pulse electroplating was used. The potentiodynamic polarization and EIS measurements indicated the highest corrosion resistance (4685 Ω.cm2) for triangle waveform compared to other waveforms. Also, it was observed that the corrosion resistance of NiCu alloy coatings was remarkably dependent on molar fraction of Cu in solid solution and crystallographic orientation. The maximum molar fraction of Cu in solid solution and growing of grains at (111) orientation result in the best corrosion resistance.