Impact of roughness of Zn-Mn coatings on corrosive stability

Abstract

This paper involves electrochemical deposition of Zn-Mn coatings from four solutions. We measured their roughness and corrosion stability. We used cathodes made of steel of unknown composition that were licensed under the chemical preparation before the electrochemical deposition of dual-Zn-Mn coatings, and we also used the anode of zinc, purity of 99.99%. Dual Zn- Mn coatings were electrodeposited for 15 minutes from all of the solutions at a current densities of 1 A/dm2, 2 A/dm2 and 4 A/dm2. All experiments were carried out galvanostatialy (at constant current) in an electrochemical cell, volume of 500 cm3 and at room temperature. The roughness of electrochemically deposited Zn-Mn coatings was measured by a TR200 device and corrosion stability of deposited coatings by determining the Electrochemical Impedance Spectroscopy (EIS). The results show that the coatings with the smallest roughness are coatings deposited at a current density of 2 A/dm2 from all of the solutions. The exception is solution 3 with the relation [Mn2+]:[Zn2+]=1:2 where the roughness is at the lowest level in comparison to all solutions, ranging from 0.71 to 0.875 μm, and the roughness is lowest at the current density of 4 A/dm2 and is 0.71 μm. Based on electrochemical measurements, the corrosive most stable Zn-Mn coating is deposited at a current density of 2 A/dm2 from all the solutions and at the current density of 4 A/dm2 from solution 3 with a ratio of [Mn2+]:[Zn2+]=1:2. This suggests that the corrosion stability is related directly to the roughness and compactness of Zn-Mn coatings. When it comes to corrosion, the most stable coatings are those with the lowest roughness.