Effects of Al2O3 Nano-additive on Performance of Micro-arc Oxidation Coatings Formed on AZ91D Mg Alloy

Ceramic coatings were prepared on AZ91 D Mg alloy by micro-arc oxidation(MAO) in aluminate electrolytes,with AlOnano-additive suspending at different concentrations.Effects of nano-additive concentration on the structure,phase composition,hardness and anti-corrosion property of the MAO coatings were analyzed by scanning electron microscopy,X-ray diffraction,micro-hardness test and electrochemical method,respectively.The results revealed that AlOnano-particles were mostly incorporated into ceramic coating chemically,transferred into MgAlO,rather than being trapped mechanically during MAO process.With the increase of AlOconcentration,the voltage-time response,content of MgAlO,hardness and anti-corrosion property increased.However,when the concentration varied from 10 g/L to 15 g/L,these behaviors and properties changed only a little.This result indicated that,after the concentration of AlOnano-additive reaching 10 g/L,the incorporation of AlOnano-particles turned into a saturation state,due to the complex process during MAO treatment.Therefore,10 g/L might be a proper concentration for MAO coating to incorporate AlOnano-particles.