Influence Of Additive On The Structure And Performance Of Micro-arc Oxidation Coating

In this paper, the specimens were treated by homemade WH-1A micro-arc oxidation(MAO) device. The influence of MgO particles in the base electrolyte on the structure andperformance of MAO coating on6061aluminum alloy was studied. Moreover, the effectmechanism of (NaPO3)6in the base electrolyte on MAO coatings formed on AZ31magnesium alloy was also investigated.The results show that the MgO particles entered into the coating by sintering of bigspark in the late stage of MAO. At1800s, compared to the coatings obtained form thebase electrolyte,the magnesium content of the coatings obtained from the electrolyte with5g/l MgO particles increased from0.38at.%to22.13at.%, while the thickness increasedfrom20.91μm to76.67μm. For the coatings obtained from the electrolyte with3g/l and5g/l MgO particles, the magnesium content was decreasing from the outer layer to theinner layer. The hardness of the MAO coating decreases with the increase of MgOparticles in the electrolyte. The best corrosion resistance of samples was obtained inelectrolyte containing1g/l MgO. The higher the content of the MgO particles in theelectrolyte is, the lower the corrosion resistance of the samples will be.In base electrolyte that contained4g/l NaOH and5g/l Na2SiO3·9H2O, the MAOcoatings cannot be deposited. It will promote the formation of the MAO coatings to add(NaPO3)6into the base electrolyte. Moreover, the thickness of the MAO coating increaseswith the increase of (NaPO3)6in the electrolyte. However, it brought about dischargeconcentration to add10g/l (NaPO3)6into the base electrolyte, and thus make the holes andcracks in the coating increased and finally corrosion resistance decreased.(NaPO3)6takespart in the formation of MAO passive film, leading the compactness of initial passive filmdecrease. The loose passive film result in concentrations discharges, and then influencesthe structure and properties of the follow-up MAO coatings.