Preparation Of Fuscous Ceramic Film On Magnesium Alloy By Microarc Oxidation And Study Of Corrosion Resisting Property

Multipurpose fuscous ceramic films on aluminium-alloy have been obtained by MAO. Therefore, different fuscous one on magnesium-alloy is needed greatly to develop because of only white ceramic film recently. Different solution systems are studied from character of MAO electrolyte, solution's conductance, pH value and ratio between different electrolytes. A new optimal electrolyte's directions is obtained for magnesium-alloy by trial and error and the effect of the fuscous ceramic films is studied by altering electrolyte's ratio and controlling different technics parameter. Then corrosion resisting property is studied for different chroma ceramic films too. Finally mechanisms of different chroma ceramic films are discussed by the way of EDS and XPS.The experiments show that the preparation of green or brown ceramic films is obtained when the ratio of concentration is 50:15:3:5, 55:30:4:20 in NaOH-Na₂SiO₃-C₆H₅OH-NH₄VO₃ solutions. Fuscous ceramic films are altered as changing voltage, current, time and temperature. The better ceramic films are obtained when voltage is between 350V and 450V, and current density is between 0.8A/dm²and 2.0A/dm² for green ceramic films and is between 1.2A/dm² and 2.4A/dm² for brown ones, time is between 5 and 20min, and temperature is between 30 and 45℃ .Otherwise is worse.The result of corrosion 5%NaCl by 120h corrosion experiments shows that the green and brown ceramic films between 350 and 450V is better in corrosion resisting than white ones, and brown ones is better green ones. The corrosion resisting property is better when current density is between 1.2A/dm² and 2.8 A/dm² for green ones, is between 0.4A/dm² and2.0A/dm² for brown ones.The analysis shows that the content of vanadium, silicon and oxygen is increased gradually, and that of magnesium and aluminum is dropped off in the ceramic films as voltage is increased. And exist mainly magnesia, silicon oxide and vanadium oxide in the ceramic films. The vanadium of green ceramic film is exist V₂O₃ and VO₂,but that of brown ones is exist a little of V₂O₃ besides V₂O₃ and VO₂. the different content of these oxide leads to come into being different chroma ceramic films, and vanadium's oxide is mainly cause for altering film's chroma. The study is sponsored by the national 10^th five year science and technology plan for tackling key problem (2001BA311A06-3), and 863 plan item (2002AA331120).