Study On Influence Of The Insulation Propertie Of Micro-arc Oxidation Ceramic Laye On Aluminum Alloy By Solution Components And Sealing Technique

The Micro-arc Oxidation (MAO) film can be used to build the high-power LED substrate for its great hardness, bonding force with the metal, corrosion-resistance, or insulating property.This essay starts from the thickness, elements, composition, and structure of the MAO film to study its insulating property, sum up the rules of changing property, search the cause of changing,and then sealing the film to promote its breakdown voltage.In the experiment, the sodium aluminate, sodium silicate, potassium chromate is used to make the electrolyte respectively, then treat the pure aluminum as the substrate to oxidized, after oxidation of 30s, 60s, 120s, 180s, 240s, 300s respectively, we make the MAO film with thickness ranging from several micron to dozens of micron. The testing method of SEM, XRD, EDS is used to detecting the surface morphology, phase composition, and element content of the film, a computer software named Image J is used to analysis the porosity of the film, the equipment called eddy current thickness meter, precision surface roughness meter is used to test the thickness,roughness of the film, and the withstand voltage tester is used to test the breakdown voltage of the film. Otherwise, it has been found from the experiment that the MAO film has better insulating property when dealing with the electrolyte which has potassium chromate in it, so we treat the substrate with electrolyte made by different concentrations of potassium chromate which is 4g/1, 6g/1and 8g/l, analyze the property after treating to find the effect of potassium chromate concentration on the properties of the MAO film. In the end, the MAO film is sealed by hydrolysis of Silane coupling agent solution in order to enhance the insulation property, the breakdown is tested again to find out the increasing amount, the surface morphology by electron microscopy at high magnification is analyzed to study the sealing effect.The result of experiment in this essay is showing following. The insulating property of MAO film is affected by thickness, phase composition, porosity in common. The different kinds of electrolyte result in several kinds of MAO films, the thickness is different and it is decided by oxide's formation rate and dissolving rate. The breakdown voltage and thickness of MAO film exists non-linear relation, the breakdown voltage is increasing slower and slower when the thickness rising. The smaller the porosity of the MAO film, the higher the degree of crystallinity,the better the insulation, and the porosity of the oxide film is closer to the higher crystallinity, the better the insulation. The potassium chromate in electrolyte can promote the formation of crystalline phase in the film, thereby increasing the insulation resistance of the film. When the concentrations of potassium chromate in the electrolyte is increased, the energy of anode reaction is reduced which lead to more low-temperature phase in the film, at the same time, the porosity is decreased. The porosity and cracks of MAO film are well-sealed by hydrolysis of Silane coupling agent solution, after the sealing, the insulating property of MAO film is greatly improved. On the surface of MAO film, the Si-OH can formed integrity of Silane film. The Silane coupling agent solution was acidic, so it may corrode part of oxide in the film, which will make the insulativity decrease.