A Comparative Study of Pulse and DC Electroplating of Zn onto Mild Steel for Improved Corrosion Resistance

In the current study, Zn electrodeposition was done from an acidic sulfate bath onto mild steel at a pH of 3.5. The Zn coating was done in both direct current (DC) and the pulsed current mode to investigate whether the two techniques would lead to a difference in the corrosion behavior of the plated films. The range of deposition current density was obtained through a systematic cyclic voltammetry (CV). The chosen current density values were - 50, - 150, - 180, and - 250 mA/cm2. Pulse deposition was done after the DC deposition at the average current density of - 180 mA/cm2 at different duty cycles, frequencies and peak current densities. The thickness of the coating was measured by using a surface profilometer and was found to be in the range of 10-28 & mu;m. Phase, structure and composition of the deposition were characterized by XRD, SEM and elemental mapping. Tafel polarization technique and electrochemical impedance spectroscopy were done to study the corrosion rate and mechanism in 3.5 wt% NaCl. A marginal increase in corrosion resistance was observed for pulse-deposited films as compared to DC-deposited ones. Films deposited at - 180 mA/cm2 and a combination of duty cycle, i.e., peak current density of - 720 mA/cm2 and at the frequency of 75 Hz, were found to have the optimum anti-corrosion performance.