A study of zinc electroplating process on mild steel for seawater application

Abstract

The study of zinc (Zn) electroplating process on mild steel (Fe) for seawater application was carried out under the combined action of electroplating and seawater application, 3.5 wt% NaCl solution. The purpose was to study the effect of varied current densities on corrosion rate and to determine the corrosion rate of zinc electroplated mild steel in seawater environment. Mild steel samples were zinc electroplated at varied current density of 2, 4 and 6 A/dm2 for 15 minutes. The plated samples were then immersed in artificial seawater environment (3.5 wt% NaCl solution) for 30 days. Weight loss was determined at intervals of five days for the duration of the exposure period. Experimental result showed corrosion attack on the zinc-plated samples over the 30 day’s immersion. The severity of attack decreases with increasing weight of zinc coated on substrate. Higher current density deposited more weight of zinc plating the mild steel samples. Mass loss was lower for substrates plated at higher current density. Results from SEM/EDS analysis had proved that electroplating at higher current density produced higher mass percentage of Zn content onto the substrate Fe. SEM was used to observe the surface morphology of the plated surface. Polycrystalline phases of a sample were characterized and identified by the X-ray diffraction pattern obtained from XRD. The most optimum microhardness value was 183.8 HV obtained by Vickers microhardness test method (MHV) for mild steel samples electroplated at 4 A/dm2 after being immersed in artificial seawater environment. The best corrosion rate of zinc electroplated mild steel plated for seawater environment was 48.0467 μm/yr possessed by sample 5 which was plated at 4 A/dm2 current density.