摘要
Owing to superior coating performance, process cost effectiveness and environmental friendliness, plasma electrolytic oxidation （PEO） attracts increasing attention for the surface treatment of lightweight metals, （A1, Mg and Ti）, to enhance their physical and mechanical properties. Plasma Electrolytic Oxidation （PEO）, also known as ＂Micro-Arc Oxidation （MAO）＂, is a high voltage plasma-assisted oxidation process uses an aqueous electrolyte to oxidize the metal surfaces to form ceramic oxide coatings which impart a high corrosion and wear resistance. The PEO process of lightweight elements is strongly influenced by such parameters as electrolyte composition and concentration, current or voltage applied and substrate alloy. Generally, these parameters have a direct influence on the discharging behavior： type, size, duration, population density and temperature. The discharges play an essential role in the formation and resulting composition of the 3-layer oxide structure, by influencing phase transformations and crystallization. This, then, affects the physical, mechanical and chemical properties of the coating. A detailed knowledge of the coating mechanisms is extremely important in order to produce a desired coating quality to reach the best performance of the PEO coatings. In PEO process, the ceramic coating grows inwards to the substrate and outwards to the coating surface simultaneously. For the coating growth, there are three simultaneous processes taking place, namely the electrochemical, the plasma chemical reactions and thermal diffusion. Optical emission spectroscopy （OES） was employed for the discharge characterization by following the substrate and electrolyte element present in the plasma discharge during the coating growth, and to determine plasma electron temperatures. The effects of process parameters during the PEO treatment were investigated using OES in the visible and near ultraviolet （NUV） band 285-800 nm. The elements present in the plasma were identified. Stark shifts of spectral lines and line intensity ratios were utilized to determine the plasma electron concentrations and temperatures, respectively.
