AUTHOR=Wang Ze-Xin , Zhang Jin-Wei , Ye Fei , Lv Wei-Gang , Lu Sheng , Sun Lei , Jiang Xi-Zhi TITLE=Properties of Micro-Arc Oxidation Coating Fabricated on Magnesium Under Two Steps Current-Decreasing Mode JOURNAL=Frontiers in Materials VOLUME=7 YEAR=2020 URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2020.00261 DOI=10.3389/fmats.2020.00261 ISSN=2296-8016 ABSTRACT=

A concept of two-steps current-decreasing mode derived from constant current mode was developed to fabricate micro-arc oxidation (MAO) coatings on ZK60 magnesium alloy in a dual electrolyte system. The growth characteristics of coatings were analyzed by voltage-time curves, and the coating microstructures were characterized by means of scanning electron microscopy. Meanwhile, the roughness, corrosion behavior, and microhardness of MAO coatings were investigated. The results show that the MAO coatings exhibit a smooth and compact surface, and have improved hardness, higher thickness, smaller roughness, and uneven distribution of holes. Such positive characteristics result in improved corrosion resistance of MAO coatings. The coating produced under the two-steps current mode of “1.2–0.6A” shows a smaller corrosion rate of 0.1559 g/m2⋅h compared with the one produced under the other mode. The results of nanoscratch tests show that the coating fabricated by “1.2–0.6 A” mode has strong bond strength with the substrate. Under this optimized mode, the MAO process also has the lowest energy consumption of 49.8 W/(dm2⋅μm).