| Ceramic coatings on 6061 aluminum alloy were prepared by micro-arc oxidation in Na2SiO3, NaAlO2, and Na(PO3)6 electrolyte systems. The breakdown voltage, thickness and hardness of ceramic coatings in different electrolyte systems were comparatively studied. The surface morphology and phase composition of ceramic coatings were analyzed using SEM and XRD techniques. The results show that the breakdown voltage is decreased with increasing of electrolyte concentration, and in Na2SiO3 electrolyte system it is the lowest, NaAlO2 takes the second place and Na (PO3)6 is the highest. In constant-current model, the thickness of ceramic coatings shows linear increase with the increment of oxidation time in electrolyte systems, growth rate remains essentially constant. The ceramic coatings in different electrolyte systems are mainly composed of α-Al2O3 and γ-Al2O3, the relative content of α-Al2O3 and γ-Al2O3 in NaAlO2 electrolyte system is higher than that in the other electrolyte systems. The hardness of dense layer is relatively high, the hardness of loose layer is rather low. The distance from substrate interface is 15 um, hardness reaches the highest (1270 HV), then it begins to reduce gradually in NaAlO2 electrolyte system. |
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