Generally, the traditional Magnesium micro-arc oxidation film of magnesium alloy first forms a dense inner layer structure on the surface of the substrate,
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and as the Magnesium oxidation process continues, the thickness of the dense inner layer continues to grow and gradually forms a loose and porous outer layer structure. Moreover, during the entire process of Magnesium micro-arc oxidation, sparks with high eruption intensity are always accompanied, and the discharge diameter of sparks can reach more than 100 μm, which is one of the reasons for the formation of a loose layer of oxide film.
If the oxide film can be regarded as a capacitor with good performance, if the charging capacity is larger, the dielectric breakdown is more likely to occur. The alternating voltage can cause the dielectric breakdown between the capacitor plates to become a conductor and release energy to form an impulse discharge.
Therefore, if the dense film is continuously affected by the impact discharge, the film layer will have local defects, and the capacitance and conductivity of the defect will increase greatly, resulting in the concentration of local micro-area discharges and larger currents. Therefore, the film layer is easier to be covered.
Electric breakdown and destruction. Furthermore, such a large residual energy will be concentrated in the large defect micro-area or coarse discharge channel to form a peak leakage current during the dielectric barrier discharge process, presenting a continuous and strong unstable spark discharge, causing a volcanic eruption effect ,
Resulting in large discharge holes, abnormally large growth of crystalline phase grains, showing a crater structure, producing microcracks, pores and other defects, and destroying the compactness and uniformity of the oxide film surface structure.
It can be seen that how to break through the traditional control process of magnesium alloy micro-arc oxidation and realize the densification and fine control of the microstructure of magnesium alloy micro-arc oxidation film has become the future development direction of magnesium alloy micro-arc oxidation process.
To this end, the project team proposed a magnesium alloy ultra-micro-arc oxidation dual-pulse control process [1-3]. By adjusting the pulse frequency, the plasma discharge spark is more dense and more uniform than the traditional micro-arc oxidation spark.
Revolutionary changes in the spark discharge mechanism of the traditional micro-arc oxidation: gradually suppress or eliminate the plasma in large defects or local concentrated impulse discharge, change the inherent characteristics of the plasma discharge in the above-mentioned traditional Magnesium micro-arc oxidation process, so that ultramicro The microstructure of the arc oxide film realizes fine control. This article will further discuss the influence of the dual pulse frequency on the microstructure and compactness of the magnesium alloy ultramicro arc oxidation film.
pulse frequency has a huge impact on the plasma discharge load and the uniformity and compactness of the magnesium alloy super MAO film. By changing the pulse frequency, the microstructure of the magnesium alloy super MAO film can be finely controlled.
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