Contribution of Seven Electroplating Factors on Some Properties of Zn-Ni Coating on Medium Carbon Steel using Taguchi's L27 Orthogonal Array

The protective Zn-alloy coating enhances the carbon steels' corrosion resistance. Seven factors of Zn-Ni coating electroplating on medium carbon steel were optimized using Taguchi L27 (37) orthogonal array. The impact of nickel chloride concentration (N), distance factor between anode and cathode (X), plating process time (P), bath temperature (T), deposition current density (I), substrate hardness (H), and substrate roughness (R) on the corrosion current density (ICorr) and the coating thickness were examined. Two different samples were also morphologically studied. Results indicated that N:20 g l-1; X:9 cm; P:20 min; T:45 °C; I:3 A dm-2; H:44 HRC; and R:P500 can produce Zn-Ni coating with the highest corrosion resistance (lowest ICorr) with inhibition efficiency of 96.5%. Among factors, T, P, H, and N had the highest impact on ICorr with a total percentage contribution of about 60%. In addition, the thickness was mainly affected by I, P, and H, with a total percentage contribution >90%. The optimal combination for lowest ICorr resulted in a smooth and more homogenous and compact structure of coating without microcracks. Higher microhardness was also obtained due to the high nickel content in Zn-Ni coating (14.7%wt). However, the worst combination gave semi-spherical-shaped crystallites with non-uniform distribution of particles.