| Technological process of rare earth conversion (REC) coating on AZ31 ally wasresearched in this paper. The effects of technical parameter s (concentrations of rareearth salts, concentrations of oxidizer, immersion time, immersion temperature ) onthe surface microstructure and corrosion properties of the coating were studied indetail. I n order to seal the micro-cracks on the conversion coatings and to improvethe corrosion resistance of these conversion coatings, multi-deposited andpost-treatment methods were carried out. T he microstructure, elements compositionof conversion coating have been examined by scanning electron microscopy (SEM)and X-ray photoelectron spectroscopy(XPS). Corrosion behavior of the conversioncoating was evaluated by polarization curves.Various surface microstructures were observed in the alloy with conversioncoating. D ifference in morphological transformations was observed on the surfacesof the conversion coating. T he most obvious technology parameter is theconcentrations of rare earth salts. P roper coating thickness could improve thecorrosion resistance. W hen the micro-cracks occurrence, corrosion resistancedecreased. In the best film t echnological process state, the magnesium alloy surfacecan quickly grow out of a membrane thickness of about 3um dense, uniform rareearth conversion film growth rate of about 50nm / s.Characterization of coatings by XPS found that the surface of the coatings wasmade up of mainly Ce O 2 and MgO in the conversion coating state. Rare earthconversion coating of magnesium alloy vertical distribution of the film, the moreclose to the inside of the higher magnesium content, the lower the content of Ce . Thedistribution of the membrane elements is continuous .T he result of polarization curves indicate that the corrosion resistance of AZ31ally is improved by REC treated. Every technical parameter have an optimal value.The corrosion resistance of AZ31 magnesium alloy is not improved bypost-treatment methods. |
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