Plasma electrolytic oxidation (PEO) is a method of oxide coatings formation on metal or alloy under anodic polarization at relatively high voltage in an appropriately selected solution. The coatings most often improve the properties of the modified material, e.g. its corrosion resistance, hardness, or wear resistance. It’s very important in the case of active metals characterized by poor mechanical properties as well as materials exposed to a corrosive environment. In the group are light metals such as aluminum or magnesium and some valve metals like titanium, zirconium, niobium, and tantalum. Anodic oxidation may be also used to improve the properties of zinc and zinc alloys. Zinc is a metal widely used to protect steel against corrosion, especially in the form of coating. To improve its corrosion resistance some conversion coatings are formed on the surface. At the moment the best conversion coating is chromate one but because of the toxic properties of chromium compounds a health-friendly, alternative coating is being sought. Because of the lower harmfulness of compounds used in the PEO process, it seems the method could be a proper way to protect zinc and its alloys.

In this study, the influence of bath composition as well as the characteristic of electric current on structure and corrosion resistance of coatings formed on pure zinc (>99.995% Zn) during the PEO process. The composition of the PEO solutions based on potassium hydroxide, sodium metasilicate and sodium metaphosphate. The effect of alternating current (AC) parameters such as current density, frequency, duty ratio was investigated. The structure of the formed oxide coatings was analyzed by scanning electron microscope (SEM) and the corrosion resistance was defined by electrochemical methods.