Study On Micro-Arc Oxidation Film Formation Mechanism Of Aluminum Alloy Based On COMSOL

Micro-arc oxidation evolved from anodization.The oxide film obtained by this method has strong corrosion resistance,friction wear resistance and insulation performance,so it has a wide range of application prospects.However,since the process of micro-arc oxidation is extremely complicated,to date,there is not yet a well-known model to explain the microarc oxidation process.Therefore,further exploration of its film formation mechanism is still needed.In this paper,taking 7075 aluminum alloy as the research object,the micro-arc oxidation film formation mechanism was studied based on the finite element method.The micro-arc oxidation film formation process of 7075 aluminum alloy was simulated by the electrochemical module of COMSOL Multiphysics.The film thickness,current density,and electric field distribution were solved.At the same time,the growth and distribution of micro-arc oxidation film was studied.The results show that the film has a thick corner and a thin middle distribution on the surface of the anode piece.Current density has the same distribution characteristics with film thickness,the insulation performance of the film cause the current density decreases with time.The corners of the work piece has the most dense electric field line and the maximum electric field strength,so this region has the maximum rate of ion movement and film formation during the reaction.A thermodynamic model of aluminum alloy micro-arc oxidation process was established,and the distribution of temperature field and thermal stress field in micro-arc oxidation thermodynamics process was studied.Using the heat transfer module and thermal stress module of COMSOL Multiphysics,the temperature/temperature gradient and thermal stress/strain distribution of the film forming process were solved.The results show that during the film formation process,the temperature of the discharge channel region is the highest,the temperature gradients on both sides of the discharge channel are the largest,and the oxide film-substrate interface plays a certain role in cooling process.The thermal stress is mainly concentrated in the discharge channel region,and gradually decreases with the increase of the radial distance and the vertical depth.With the increase of cooling time,the thermal stress inside the oxide film gradually decreases and tends to become stable,and becomes a residual stress.Based on the distribution characteristics of temperature field and thermal stress field,the effect of micro-arc oxidation thermodynamic process on the surface morphology of the film was studied.The results show that the uneven cooling rate in different region causes the crater-like hole on the surface of the film layer.The existence of residual stress in the film layer which is greater than the tensile strength of the material is the main reason for the micro-cracks on the surface of the film layer.Based on the numerical simulation conditions,the micro-arc oxidation experimental platform was set up,and the micro-arc oxidation ceramic film layer was prepared by experiments.The thickness of the film was measured by scanning electron microscopy,and the experimental data were compared with the numerical simulation data.The results show that the difference between the two data is small and within the acceptable error range.This verifies the accuracy and feasibility of the numerical simulation method,which can provide reference and basis for the study of micro-arc oxidation mechanism.