Characteristics of microarc oxidation coatings deposited on magnesium using alkaline and acidic electrolytes in a single stage as well as using dual electrolytes in two stages

Microarc oxidation (MAO) of magnesium is performed in a single stage using an alkaline silicate electrolyte and acidic zirconate electrolyte as well as in two stages, sequentially using the alkaline silicate followed by the acidic zirconate electrolyte. The morphological characteristics, surface roughness, phase content, corrosion behaviour and bioactivity were compared. The surface morphology, thickness, average surface roughness (R_a), and phase composition of the MAO coatings show a strong dependence on the type of electrolytes used and the methodology employed for deposition. Based on the corrosion protective ability in Hank's balanced salt solution, the uncoated and MAO coated Mg are ranked as follows: Uncoated Mg < MAO coated Mg prepared using alkaline silicate electrolyte < MAO coated Mg prepared using acidic zirconate electrolyte < MAO coated Mg prepared in two stages, sequentially using the alkaline silicate followed by the acidic zirconate electrolyte. Poorly crystalline calcium deficient apatite is formed on all samples after immersion in SBF at 37 °C for 240 h.