Fluoride influence on the properties of oxide layer produced by plasma electrolytic oxidation

Plasma Electrolytic Oxidation (PEO) is a powerful technique allowing hardening and corrosion protection of valve metals due to formation of an oxide layer on the metal surface. The addition of fluoride ions to the alkaline electrolyte for the PEO processing of aluminum and magnesium alloys produces significant changes in the structure and properties of the coating [1-3], however the mechanism of these changes is not clear. A study of the influence of the fluoride concentration on the composition, structure and morphology of thin (to 20 μm) PEO layers was performed. The oxide layer thickness on aluminum is significantly smaller than that on magnesium. Fluorine is detected as an amorphous phase in the vicinity of the base metal.