Aluminium Alloy Micro-Arc Oxide Film Growth Mechanism And Performance Research

MAO coatings are widely used in aviation, aerospace and other fields because of good wear resistance, corrosion resistance and other properties. In order to further study the MAO, respectively prepared MAO coatings and ZrO₂ composite coatings on pure aluminum in the Na₂SiO₃-Na₅P₃O₁₀-CH₃ COONa electrolytic liquid. Through SEM to observve coatings surface, MAO middle layer, MAO coatings /substrate interface and the cross-section morphology and by using EDS and XRD analysis of elements and phase respectively.To preliminary grope for coatings growth mechanism and composite coatings growth mechanism.On the basis of theoretical research, prepared composite coatings that formed on Al-Si cast alloy by MAO in electrolyte with α-Al₂O₃ particles and study its wear resistance and corrosion resistance.The results show that the growth of coatings formed on pure aluminum was two opposite direction. The initial stage, MAO coatings was given priority to with outward growth; Middle and late, the inside growth plays a leading role. Through the MAO coatings surface, MAO middle layer and MAO coatings /substrate interface can be seen there are discharge hole of same size throughout the MAO coatings, and interface morphology has been changing. Preliminary thought in the process of MAO, high temperature and high pressure makes the discharge area formed the molten pool and changed substrate. some molten product directly deposited and filled the consume of substrate, some other sprayed out through plasma channel and left hole in the MAO coatings. Through the establishment of MAO growth model to account for two-way growth model, the changes of morphology and structure, As well as the importance of the existence of discharge hole and molten pool to coatings growth.From outside to inside of MAO/ZrO₂ composite coatings, the ZrO₂ average contents were 17.64%, 6.85% and 7.17%. The initial stage, the anodic oxide films were thinner, so ZrO₂ particles can be easily embedded in the coatings, and the weak area were formed between particles and particles. Began to discharge on sample surface, anodic oxidation film between the particles were first discharge to breakdown and formed molten pool. Under the high temperature and high pressure, the molten material sprayed outward and covered particles.As MAO/ZrO₂ composite coatings thickening, ZrO₂ particles mainly were captured by molten pool into the coatings. Preliminary ZrO₂ particles deposition model was established from the above conclusions: ZrO₂ particles participated and changed the process of anodic oxide film; Then ZrO₂ particles mainly through discharge hole and molten pool work together into the coatings.α-Al₂O₃ particles changed the composition and structure of the casting Al-Si alloy MAO coatings and improved the wear resistance and corrosion resistance. Not add α-Al₂O₃ particles, MAO coatings structure were porous, main phase were γ-Al₂O₃. In turn, to join the α-Al₂O₃ particles, MAO/α-Al₂O₃ composite coatings became density and lower roughness（Ra）. The friction coefficient of MAO/α-Al₂O₃ composite coatings are 0.20⁰.20, And the friction surface only had small wear spots, the wear rate were 0.77x10^-6mm3? N^-1?m^-1, only 14% of the substrate and 65% of the MAO coatings. In addition MAO/α-Al₂O₃ composite coatings of pore structure resistance Rp and dense structure resistance Rb were greater than MAO coatings of Rp and Rb. Moreover the MAO/α-Al₂O₃ composite coatings of corrosion current density were 4.23x10^-6 A?cm^-2, below the MAO coatings about one order of magnitude, and resistant to salt spray test time was 1440 h.