Study On Bonding Strength And Compact-Ability Of Ceramic Coatings Formed By Micro-Arc Oxidation On Magnesium Alloys

The bonding strength and its influencing factors of ceramic coatings formed by micro-arc oxidation (MAO) on MB8 magnesium alloys were studied by shearing test, surface and cross-section morphology for fracture surface of ceramic coatings. Breakdown test and SEM analyzed the regularity influenced of energy parameter on dielectric strength of ceramic coatings. The mechanism and its influencing factors of salt spray corrosion of ceramic coatings by MAO on magnesium alloys were discussed by salt spray test and X-ray. The internal relationship between the dielectric strength and corrosion resistance of ceramic coatings by MAO was analyzed and discussed.The result indicates that the bonding strength of ceramic coatings included layer-base bonding strength and itself cohesion force, which represents the tendency of decreasing with current density and solution conductivity increasing, and the bonding strength of ceramic coatings represents the tendency of increasing in beginning and reducing at last, and best-treatment time on MB8 magnesium alloys is 30min. The energy of MAO is higher, and micro-metallurgical bonding of ceramic coatings is higher, and the layer-base bonding strength of it is also better. But the bigger energy will influence compact-ability of ceramic coatings, and reduced cohesion force of ceramic coatings. The dielectric strength of ceramic coatings represents the tendency of reducing with current density and duty cycle increasing,and it represents the tendency of increasing with frequency increasing. The key to get compact and dielectric strength ceramic coatings is to control the electrical parameter in different growth moment. The corrosion type of ceramic coatings is pointed corrosion, and its corrosion process is pitting corrosion core formation and growth process, namely MgO phase hydration and generation Mg(0H)2. Increasing compact-ability of ceramic coatings may effectively increase corrosion-resistance of ceramic coatings. The surface contact angle of ceramic coatings is smaller, its corrosion-resistance is worse; the surface contact angle of ceramic coatings is bigger, its corrosion-resistance is better. The dielectric strength and corrosion-resistance properties of ceramic coatings by MAO on magnesium alloys are relation to the compact-ability. The compact-ability of ceramic coatings is better, and its dielectric strength and corrosion resistance properties are also better.