Optimization Of Electrical Parameters For Micro Arc Oxidation Of Aluminum Alloy Based On Subsection Control

7075 aluminum alloy has high toughness,hardness,strength and excellent processability.It has been widely applied in aviation,aerospace and other fields.However,the corrosivity and scour of the sea water and the high speed of the aircraft all put forward extremely demanding requirements for the corrosion resistance,wear resistance and high temperature resistance of the parts and components.Micro arc oxidation technology can grow ceramic coating on the surface of aluminum alloy.It can greatly improve the corrosion resistance,wear resistance,high temperature oxidation resistance and insulation properties of the 7075 aluminum alloy.During the growth process of micro arc oxidation film,the discharge breakdown of plasma will inevitably lead to the formation of micro pores in ceramic coatings.The more micropores of the ceramic coating,the lower the compactness,which will significantly reduce the surface adhesion,corrosion resistance,wear resistance and high temperature resistance of the ceramic coating.At present,the experimental study of micro arc oxidation generally uses constant electrical parameters,but the thickness of the film increases continuously during the actual reaction process,and the surface morphology changes gradually.The breakdown voltage,the required energy and the cooling time are also changed,and the constant electrical parameters can not adapt to the change.Therefore,it is necessary to adjust the electrical parameters to adapt to the actual reaction in the process of reaction.In order to solve the above problems,the forward voltage,current density,positive duty ratio and pulse frequency of the 7075 aluminum alloy micro arc oxidation process are optimized.Then,based on the optimized electrical parameters,the subsection control of the forward voltage is carried out by using the self-developed PC control software.Using the orthogonal experiment method,the electrical parameters of the 7075 aluminum alloy surface micro-arc oxidation process were optimized by using the thickness and porosity of the ceramic film as indicators.The electrical parameter optimization experiment results show that the order of the electric parameters affecting thethickness of the film is the forward voltage>current density>positive duty ratio>pulse frequency;the order of the electric parameters affecting the porosity is the forward voltage>current density>pulse frequency>positive space ratio;the electric parameters optimized by the comprehensive balance method are positive voltage 550V,current density 8A/dm2,positive duty ratio 20%,frequency 400Hz.Based on the optimized electrical parameters,the reaction process of micro-arc oxidation on the surface of 7075 aluminum alloy was divided into three stages.The reaction lasted for about 30 minutes and the timing of the control of forward voltage was controlled as follows:Stage 1:Omin-5min anode deposition and spark discharge phase;Stage 2:5min-25min micro-arc oxidation phase;Stage 3:25 min-30 min arc discharge phase.Based on C#,a PC control software is developed,and the forward voltage is controlled by piecewise control of micro arc oxidation process.The results show that the order of the film thickness is second stage>third stage>first stage.When the second stage voltage is 525V,the third stage voltage is 500V and the first stage voltage is 550V,the thickness of the film layer is maximum.The time sequence of the film porosity is the third stage>second stage>the first stage and the third stage voltage.For the 500 V,second stage voltage 550V and the first stage voltage 525V,the film porosity is the smallest.