| Micro arc oxidation(MAO)is a kind of surface treatment technology to grow oxidized ceramic film on the surface of metals and alloys,it is widely used in aerospace,shipbuilding,engine manufacturing and other fields,because it can greatly improve the wear resistance and corrosion resistance of materials.The common methods used MAO currently include immersion type and scanning type.Both methods have disadvantages.The former has high energy consumption,while the latter has unstable electrolytes and difficulty in accurate film formation.Aiming at the above problems,a set of low-power micro arc oxidation moving cathode macro scanning system is designed in this paper;Aiming at the system,the selection and optimization methods of micro arc oxidation process parameters on aluminum alloy are studied,so as to realize the targeted control of different properties of the generated oxidation film.The specific search procedure is as follows:The basic functions of the moving cathode scanning system such as scanning path control,electrolyte cooling circulation and electrolyte stirring were realized by the laser engraving machine,small cycle refrigerator and small oxygenation pump.The keys of the scanning system of movable cathode were the moving cathode morphology and the electrolyte injection device.The optimal moving cathode morphology was determined by comparative experiments of different moving cathodes and finite element analysis,aiming at the uniformity of film formation.An electrolyte injection device was designed and made aiming at the stability of the electrolyte layer between the two electrodes.Then,finite element analysis was conducted.The orthogonal experiments under the condition of fixed movable cathode were used to study the effects of positive voltage,reverse duty cycle and pulse frequency on properties of oxide film.The selection and optimization method of electrical parameters for targeted control of properties of oxide film was designed.Using this method,the optimal electrical parameters required for subsequent tests were designedThe influence of the reaction time on properties of oxide film was analyzed by movable cathode fixed-point scanning test.Taking into account the quality and efficiency of film formation,the optimal reaction time parameters were preliminarily determined.The relationship between the reaction time and the equivalent time was studied by the linear scanning test of movable cathode.The equivalent time method was used to compare the difference of the sample performance obtained by fixed-point scanning test and linear scanning test,so as to study the influence of scanning path on properties of oxide film.In addition,the effect of reaction time on the properties of the film under the condition of moving cathode was studied to further determine the optimal equivalent time parameter.The area scanning test of movable cathode was carried out to test the effect of micro arc oxidation treatment of the designed device and the optimization method of process parameters.The thickness of micro arc oxidation film was 25.6?m,the roughness was1.048?m,the hardness was 845.3HV,the self corrosion potential was-0.661V,the self corrosion current was 1.03178×10-7A/cm~2.The targeted improvement of main properties such as film hardness and thickness was accurately realized,while the secondary properties such as roughness and corrosion resistance were taken into account.After calculation,the maximum average output power of the power supply was 197.2W and the film-forming speed of oxidation ceramic coating was 1.009cm~2/min.The low power of micro arc oxidation treatment was realized,and film-forming speed was guaranteed at the same time. |
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