Anodizing of Zinc-Titanium Alloy in NaOH and KOH Baths

Abstract

Electrochemical process of conversion coatings formation on Zn-Ti alloy surface during one-step anodizing process was studied in NaOH and KOH electrolytes over the range of voltages (4-50 V) and constant time in order to investigate parameters for the origin of anodic zinc coating. Stainless steel was used as a counter electrode and electrolyte during the anodizing process was agitated by compressed air. Coatings microstructures and morphology were characterized by means of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Surface topography was investigated prior and after the anodizing using non-contact optical 3D profilometer. It was found that high voltage (50 V) and low concentrations of electrolyte (0.04 and 0.1 mol/L NaOH) led to origin of white coloured oxide coatings, while lower voltage (4 and 6 V) and higher concentrations of electrolyte promote the origin of black coloured oxide coatings. Concentration of electrolyte and voltage influenced the thickness of conversion coatings and its surface morphology. Moreover, the surface morphology of the coatings was also influenced by the heterogeneity of substrate alloy.