Preparation And Investigation Of Properties Of Microarc Oxidation Coatings On AZ91D Magnesium Alloy And The Preparation Of Composite PTFE-MgO Coatings

In the present work, Ceramic coatings were formed by micro-arc oxidation on magnesium alloy in two different electrolytes:Na2SiO3system and NaAlO2system. The morphology and phase composition of the coatings were investigated by field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD). The surface roughness of the coatings was characterized by confocal laser scanning microscopy (CLSM). Simultaneously, the tribological and corrosive properties of the composite coatings were evaluated by using a universal materials tester (UMT), and a IVIUMSTAT automatic laboratory corrosion measurement system. The results shows that ceramic coatings fabricated in NaAlO2electrolyte had more micro-pores in quantity and less size in diameter compared with the ceramic coatings formed in Na2SiO3electrolyte. There are apparent perforated flaws on the surface of ceramic coatings formed in NaA102electrolyte. In contrast, ceramic coating formed in25g/l Na2SiO3electrolyte was more smooth and compact, therefore, the better comprehensive properties were shown.On the basis of determining the main film-forming agent, the ceramic coatings were fabricated under different process parameters. By virtue of detection and analysis, the better experimental parameters were determine as follows:25g/l Na2SiO3,5g/L NaOH,1g/L boric acid, PH value in the range of10-12, current density:5A/dm2, current frequency:600Hz, oxidation time:20min.To further improve wear resistance and corrosion resistance of ceramic coating, on the basis of optimized process parameters mentioned above, composite coatings(MgO-PTFE) were successful fabricated in the electrolyte containing PTFE with different concentrationlml/L,2ml/L,3ml/L). The result shows that PTFE can deposit in the ceramic coating by physical diffusion and electrophoresis. Ceramic coating formed in electrolyte containing lml/L PTFE had smaller micro-pores in size compared with the ceramic coatings formed in electrolyte without PTFE, and the majority of micro-pores were blocked up by PTFE, the better wear resistance and corrosion resistance properties were shown.