Micro-Arc Oxidation /Modified/ Sealing Process Of Mg-Li Alloy And Its Corrosion Resistance

Micro-arc oxidation (MAO) technology could only meet the needs of the metal substrate against corrosion to some extent, However, porosity and micro cracks of the coating on the surface was the most important factor for the corrosion resistance. Therefore, modification of the electrolyte formulation and development of complex post-processing technology of the MAO coatings became the research focus and direction of MAO technology. Only through the sealing of holes can implementa the performance of the consolidation and strengthening of the film better. In this subject we used NaAlO₂ electrolyte systerm to Preparate the MAO film on Mg-8wt% Li alloy sheet which had good corrosion resistance, then preperation, doping and brush methods were carried out on the MAO film, which were mean to modifiy and seal the MAO film respectively.By recording the cell voltage and the breakdown voltage changes occurred in MAO process were analyzed. The fused degree and holes on the film were demonstrated by scanning electron microscopy (SEM). The elements and crystalline phases, the membrane of the film, were detected by Electron Spectrometer (EDS) and X-ray diffraction (XRD). The bonding strength of the film were measured by shearing method. Corrosion resistance were assessed by Tafel ,cyclic voltammetry and corrosion area in the test of salt spray.There was a ceramic coating formed on Mg-8wt% alloy in NaAlO₂ electrolyte By MAO technology. During the electrolyte concentration reasearch and optimizati- on of electrical parameters we study their impact on structure and uniform corrosio-n resistance of the ceramic membrane, which mainly composeγ-Al₂O₃ andMgAl₂O₄ and possess good corrosion resistance that the corrosion current density of the sub- strate reduced from the original -4 th to -6 th.Phytic acid improved the performance of MAO film from the two aspects which were morphology and composition. The modified structure of the film, general corrosion resistance, pitting corrosion resistance were characterized. The fragment of organic conversion film incoperated into the ceramic coating after the way first by Phytic acid preperation then by MAO treatment. The way doping phytic acid directly to the electrolysis made the film more thicker and corrosion resistance more better, which, by adding 4g/L the film manufactured behave the best resistant to general corrosion and adding 2g/L the film received the best resistant to pitting corrosion.During sealing process of the optimized MAO coating, the two sealing agents, Na₂MoO₄ and Epoxy/nano SiO₂ were used. However, sealing effects of molybdate soaking was limited. In contrast, after brushing epoxy the film had strong ability to resist the corrosion, especially when the resin hybridizated with 1wt% nano-SiO₂, the corrosion current could low down to -9 power, after 15 days salt spray test the membrane could maintain their integrity basically.