Microarc oxidation behaviors of SiC_w/AZ91 Mg alloy matrix composite and corrosion resistance of the coatings

Protective coatings were fabricated on the surface of SiC_w/AZ91 Mg alloy matrix composite by microarc oxidation (MAO) surface treatment technique. Microarc oxidation behaviors of the composite were compared with AZ91 Mg alloy. The corrosion resistance enhancement of the composite after MAO treatment was also evaluated by electrochemical method. The results show that the microarc oxidation behaviors of the composite are different from those of the alloy because the presence of SiC whisker has influenced the formation of barrier film at the initial stage of MAO. Compared with the alloy, the composite doesn't exhibit ideal voltage evolution trend during MAO, especially at the early stage of MAO. For the composite, the time corresponding to occurrence of dielectric breakdown is longer than that of the alloy. Nonetheless, the corrosion resistance of the composite still is improved by the MAO coating. After the composite is coated by MAO, the corrosion current is decreased and the corrosion potential is increased.