Effects of reinforcement phases in magnesium matrix composites on microarc discharge behavior and characteristics of microarc oxidation coatings

The ceramic coatings were synthesized on AZ91 Mg alloy, Al(18)B(4)O(33)w/AZ91 and SiCw/AZ91 Mg matrix composites by microarc oxidation (MAO) technique in an alkali-silicate electrolyte solution. The microarc discharge phenomena of the three substrates during MAO process were described. SEM and XRD were employed to characterize microstructure and phase composition of the coatings. The corrosion resistance of the coatings was evaluated by electrochemical method. The results show that the three substrates have different voltage span of microarc discharge and different voltage evolution trend with increasing period during MAO. As a consequence, mass gain after oxidation and microstructure of coatings are also different for the three substrates. These MAO behaviors are believed to be attributed to the addition of reinforcement phases with different properties. The reinforcement phases in the composites have no influence on the phase composition of MAO coatings. MAO treatment could improve the corrosion resistance of Mg alloy and composites to different extent. (c) 2005 Elsevier B.V. All rights reserved.