Simultaneous improvement of wear and corrosion resistance of microarc oxidation coatings on ZK61 Mg alloy by doping with ZrO2 nanoparticles
The poor corrosion resistance of magnesium (Mg) and its alloys limits their application in various fields. Micro arc oxidation (MAO) coatings can improve the corrosion resistance, but the pore defects and low surface hardness make them susceptible to wear and accelerated corrosion during usage. In this study, a ZrO 2 nanoparticles doped-MAO coating is prepared on the ZK61 Mg alloy by utilizing an MgF 2 passivation layer to prevent ablation. The ZrO 2 nanoparticles re-melt and precipitate due to local discharging, which produces evenly dispersed nanocrystals in the MAO coating. As a result, the hardness of the MAO coating with the appropriate ZrO 2 concentration increases by over 10 times, while the wear rate decreases and corrosion resistance increases. With increasing ZrO 2 concentrations, the corrosion potentials increase from −1.528 V of the bare ZK61 Mg alloy to −1.184 V, the corrosion current density decreases from 1.065 × 10 –4 A cm –2 to 3.960 × 10 –8 A cm –2 , and the charge transfer resistance increases from 3.41 × 10 2 Ω cm 2 to 6.782 × 10 5 Ω cm 2 . Immersion tests conducted in a salt solution for 28 d reveal minimal corrosion in contrast to severe corrosion on the untreated ZK61 Mg alloy. ZrO 2 nanoparticles improve the corrosion resistance of MAO coatings by sealing pores and secondary strengthening of the corrosion product layer.
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