Characterization of AZ31 Mg Alloy coated by plasma electrolytic oxidation

In this study, AZ31 Mg alloy produced by twin roll casting was coated by a plasma electrolytic oxidation (PEO) in the solution, consisting of Na2SiO3·5H2O + KOH electrolyte at 0.085 A/cm2 current density for 15, 30, 45 and 60 min. Thickness of the coated layer, surface morphology, phase structure, hardness, adhesion strength of the layer and wear resistance were analyzed by an eddy current, SEM, XRD, Vickers hardness, micro scratch tester and tribometer, respectively. The average coating thickness ranged from 17 to 56 μm. A number of pores were formed on the coated layer. XRD revealed that Mg2SiO4 (Forsterite) and MgO (Periclase) phases were formed on the surface of the magnesium alloy. Average coating hardness was measured as 660 HV, while the hardness of the magnesium alloy was 72 HV. Adhesion strength of coatings was increased by increasing duration time. Wear resistances of coatings were higher than AZ31 Mg alloy.