Evaluation of Formic Acid and Cyclohexylamine as Additives in Electrodeposition of Zn Coating

Abstract

The Zn coatings obtained through electrodeposition are used to protect steel substrates from corrosion. In general, organic additives are added to the deposition bath in order to improve deposition characteristics such as corrosion resistance, hardness and deposition efficiency. Despite of the literature present information about the various organic additives effects on Zn coating properties there is no analysis of organic compounds with free electron-containing radicals, such as formic acid and cyclohexylamine. The formic acid has oxygen atoms with free electrons, whereas cyclohexylamine contains nitrogen with free electrons. Aiming at overcoming this gap, this manuscript presents an analysis of the effect in addition of formic acid mixture and cyclohexylamine on the deposition flow efficiency, corrosion resistance, hardness, roughness and micro-structure of Zn coating on carbon steel AISI 1020. The corrosion resistance evaluation was performed by potentiodynamic polarization determined by polarization resistance and weight loss tests as well. The analisys of morphology and electrodeposited microstructures were made by the Scanning Electron Microscopy (SEM) and Spectrometry X-Ray Diffraction (XRD). The Zn coatings were obtained from chloride deposition baths at constant pH 5. Results showed that corrosion resistance in the 0.5 mol/L NaCl solution of Zn coatings increases with the addition of the mixture of the formic acid and / or cyclohexylamine. Also, the corrosion resistance is higher with mixture than with additives alone. The addition of the mixture formic acid and cyclohexylamine increases the basal plane presence (0 0 2). However, the basal plane presence (0 0 2) does not increase when formic acid and cyclohexylamine are added alone which indicates a synergic effect of formic acid and cyclohexylamine in in the plan promotion (0 0 2). Also, was observed that an addition of formic acid mixture and cyclohexylamine increases the current deposition efficiency, decreases the roughness and raises the Zn coating hardness.

Keywords:
Electrodeposition, Zinc; Additives, Corrosion, Formic acid, Cyclohexylamine