The Study Of The Binding Force And Corrosion Resistance Of The Composite Coatings Treated By Micro Arc Oxidation And Electrophoresis On Magnesium Alloy

The electrophoresis coating which had some thickness were prepared on the surface of ceramic coating of AZ31 magnesium alloy using micro arc oxidation and electrophoresis technology.The binding mechanism of the composite coatings was analyzed.The connecting corrosion resistance and scraping corrosion resistance of the composite coatings were discussed. The surface morphologies of ceramic coatings treated by micro arc oxidation and cross-section morphologies of composite coatings treated by micro arc oxidation and electrophoresis were observed by SEM.The binding force of the composite coatings was reviewed by circle cut test. The thickness of ceramic coatings and electrophoresis coatings was measured by eddy current thickness gauge.The roughness of ceramic coatings was tested by JJI-B surface roughness measure gauge.The changing of the functional group of the coatings treated by different technology was analyzed by FT-IR spectra.The connecting corrosion resistance between the samples of magnesium alloy which was treated by micro arc oxidation and electrophoresis and aluminium alloy was investigated by salt spray test,and also the scraping corrosion resistance of composite coatings was studied.The mechanism of connecting corrosion resistance of composite coatings was discussed.The results indicate that the binding force of composite coatings treated by micro arc oxidation and electrophoresis is better than that of composite coatings treated by chemical conversion and electrophoresis.The main factors of affecting the binding force of composite coatings were that wetting conditions of substrate surface,effect of chemical bond of the interface.When the roughness of ceramic coatings treated by micro arc oxidation is ranged from 0.66μm to 2.25μm,the grade of the binding force of composite coatings is 1.The binding force of the composite coatings was affected little when the thickness of ceramic coatings was ranged from 2.2μm to 13.46μm,and the grade is also 1.The corrosion experiments shows that the scraping corrosion resistance of composite coatings treated by micro arc oxidation and electrophoresis is better than that of the coatings treated by direct electrophoresis or chemical conversion and electrophoresis.The corrosion process is that corrosion substances permeate the electrophoresis coating into the substrate,and then spread along the surface of the substrate. The scraping corrosion resistance is affected greatly by the binding force of the composite coatings and the electrochemistry stability of the substrates.The sample of magnesium alloy treated by micro arc oxidation and electrophoresis is connected by aluminium alloy under 432h salt spray test,and the lose weight is only 0.44g/m~2,which is far better than that of magnesium alloy treated by micro arc oxidation.The connecting corrosion resistance of composite coatings is affected little by micro arc oxidation time,and the corrosion rate is all about 0.4g/m~2.The mechanism of connecting corrosion resistance of composite coatings is that the corrosion voltage of composite coatings is higher than that of ceramic coatings,and the corrosion batteries under corrosion systems are difficultly formed because of high impedance and binding force of composite coatings,which avoid the galvanic corrosion and slit corrosion occurring.