Study On The Performance Of Al-CO Layers And Micro-arc Oxidation Coatings

In AlCl3-NaCl-KCl molten salts, the Al-Co layers were electrodeposited on Q235steel surface. The influences of different contents of CoCl2for Al-Co coatings werestudied. The surface morphology, elementary composition and organizational structure ofthe layers were investigated by means of scanning electron microscopy (SEM), energydispersive spectroscopy (EDS) and X-ray diffraction (XRD). The corrosion resistance ofthe layers was analyzed by the Tafel curves and anodic polarization curve in3.5wt%NaCl solution. The results indicated that the Al-Co alloy layers could be obtained afteradding CoCl2in the molten salts; the layers were mainly composed of Al and Al9Co2；there are enormous influences for the Al-Co alloy layers by adding different cocents ofCoCl2. The corrosion resistance and hardness of the Al-Co alloy layers were better thanothers when the Co concent was9.68%in the layers. The corrosion resistance of the layerswas better after adding NdCl3and DyCl3.The layers were transformed into micro-arc oxidation coatings by the micro-arcoxidation. The impacts of the Co concent in the layers, NdCl3and DyCl3, the concentrationof sodium silicate and sodium hydroxide and different kinds of additives were tested. Theorganizational structure and surface morphology of the Al-Co micro-arc oxidationcoatings were tested by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The corrosion resistance of the micro-arc oxidation coatings was analyzed by the Tafelcurves and electrochemical impedance spectroscopy (EIS) in3.5wt%NaCl solution. Theresults showed that the well-distributed micro-arc oxidation coatings could be obtained.The micro-arc oxidation coatings were mainly composed of Al, Al2O3and Al9Co2. Thecorrosion resistance, thickness and hardness of the Al-Co micro-arc oxidation coatingswere better than others when the Co concent is9.68%in the layers. The corrosionresistance of the Al-Co micro-arc oxidation coatings was improved when NdCl3and DyCl3were added to the molten salts.There were different influences for the corrosion resistancewhen KClO3, KMnO4and C12H25SO4Na were added to the electrolyte.