Influence of current density and temperature in the zinc electroplating process at sulfate-based acid solution: study on process efficiency and coating morphology

Abstract

Zinc as a metallic coating is a common strategy to protect the carbon steel against corrosion. The most common process of zinc deposition is known as electroplating. Because of the high toxicity of cyanide-based baths, the interest in acid baths has grown, but they present many challenges to be overcome. Several operational parameters and bath constitution – such as current density, pH, and zinc concentration – can impact the current efficiency, deposit quality, and coating morphology. In this work, the process efficiency and the coating morphology were evaluated on electroplated AISI 1008 carbon steel samples. The current density and temperature were individually varied on a range from 7.5 mA.cm^-2 to 30.5 mA.cm^-2, and from 40 °C to 60 °C, respectively. The process efficiency was evaluated by current efficiency (e_C). The surface morphology was analyzed by both optical microscopy (OM) and scanning electron microscopy (SEM). Varying the bath temperature did not promote impacts in the current efficiency, which remained in all temperatures evaluated over 95%. On the other hand, increasing the current density, increased the current efficiency, starting from (85 ± 2)% at 7.5 mA.cm^-2 to (92 ± 2)% at 19.0 mA.cm^-2, and (95 ± 1)% at 30.5 mA.cm^-2. Through OM and SEM analysis, the increase in the temperature tended to turn the coating rougher, and the sample was not completely covered at 7.5 mA.cm^-2. Therefore, we recommend the use of a temperature between 40 °C and 50 °C associated with a current density of 30.5 mA.cm^-2.