In this study, the effects of zinc (Zn) and silicon (Si) ions on the corrosion behaviors of a Ti-6Al-4V alloy treated with plasma electrolytic oxidation (PEO) were analyzed using various experimental instruments. The PEO of Ti-6Al-4V was carried out in electrolytes with Zn contents of 0, 5, 10, and 20 Mol%. To investigate the corrosion behaviors, a potentiodynamic test was conducted and the alternating-current (AC) impedance behaviors were examined in a 0.9% NaCl solution at 36.5 +/- 1.0 degrees C. The morphology and structure were examined by field-emission scanning electron microscopy, and an elemental analysis was performed using energy-dispersive X-ray spectroscopy. The mechanical properties of the coating surface were investigated by roughness and scratch tests. The PEO-treated surface showed that the pore size is dependent on the ion content of the electrolyte, and the size and number of pores increased with Zn content. In the case of the Zn/Si sample, the pore size was larger. The maximum size of the pores decreased and minimum size of the pores increased up to 10Zn/Si, and Zn and Si affected the formation of pore shapes. In the case of the PEO-treated surface, the corrosion potential (E-corr) and corrosion current density (I-corr) were lower, and the current density in the primary passivation (I-pp) was more stable than in the Ti-6Al-4V sample. As the Zn content increased, the capacitances of the barrier and outer porous layers decreased, and the polarization resistance of the barrier layers increased. (C) 2017 Elsevier B.V. All rights reserved.