Study On The Composite Technology And Coatings Treated By Micro-Arc Oxidation And Electrophoresis Of Magnesium Alloy

The composite coatings which content the requirements of appearance were prepared on AZ31 magnesium alloy using micro-arc and electrophoresis technology. The binding force、 compactness and corrosion resistance of composite coatings were investigated. The surface morphologies of micro-arc oxidation ceramic coatings and cross-section morphologies of micro-arc oxidation and electrophoresis composite coatings were observed by SEM. The compactness of electrophoresis coatings was analyzed by withstanding voltage test. The binding force of composite coatings was investigated by cross cut test. The thickness of ceramic coatings and electrophoresis coatings was measured by eddy current thickness gauge. The changing of the functional group of electrophoresis coatings surface was analyzed by XPS. The corrosion resistance was compared by salt spray test and electrochemical test between the samples treated by micro-arc oxidation and composite treatment. The effect of composite technologies on the corrosion resistance of composite coatings was investigated by acid and alkali resistance experiments.The results indicate that there is corrosion on ceramic coatings on magnesium alloy by micro-arc oxidation after salt spray testing 75h. But there is not corrosion on composite coatings after salt spray testing 800h. The results of polarization curves indicate that the corrosion current of samples treated by micro-arc oxidation is 170μA and that of samples treated by composite technique is only 3.94nA. The binding type of composite coatings is mainly physical binding presented by acting force among molecules and mechanical gnathodynam, which is more intensive than direct electrophoresis. The alkali resistance of composite coatings is all excellent. The acid resistance of composite coatings is more excellent than coatings prepared by direct electrophoresis. The acid resistance of composite coatings treated by micro-arc oxidation and cathode or anode electrophoresis is all excellent. The binding force and cid resistance of composite coatings is improved by the increasing of micro-arc oxidation time. The binding force of composite coatings treated by drying 10 minutes at 80℃ between micro-arc oxidation and electrophoresis is best, which exhibit excellent acid resistance. The compactness of composite coatings treated by 30V electrophoresis is better, but the binding force is worse, so acid resistance of which are better at the beginning of corrosion, through the test, the cid resistance of composite coatings treated by 100V electrophoresis is best. The dielectric intensity of composite coatings treated by different electrophoresis time is increasing first, and then decreasing, and the time of the maximum is between 2 and 3 minutes, then which exhibit excellent acid resistance. The compactness of composite coatings solidifying 40min at 215℃ is best, so is the acid resistance. The main factors restricting the corrosion of composite coatings are binding type and the value of binding force among composite coatings, and the compactness of electrophoresis coatings.