Preparation,Microstructure And Properties Of Micro-arc Oxidation Film Of Aluminum Matrix Composites

Aluminum Matrix Composites?Al MMCs?are widely used in military defense,aerospace and other industrial fields.The micro-arc oxidation?MAO?technology can improve the surface hardness and corrosion resistance of the Al MMCs.In order to study the preparation and properties of MAO film in details,Si C_p/6092 aluminum matrix composites were treated by micro-arc oxidation in sodium silicate electrolyte.The effects of electrolyte concentration and temperature on the microstructure and properties of MAO film were investigated,and the growth behavior of the film was analyzed by observation.The results showed that,the increase of experimental temperature or the concentration of Na₂Si O₃ in electrolyte would increase the thickness of oxide film.When the temperature was25?and the concentration of Na₂Si O₃ was 0.09mol/L,the average thickness of the film reached the maximum of 52.7?m.When the temperature was 40?,the growth of the film will be inhibited.The oxide film was composed of two layers,the inner dense layer and the outer loose layer.A large number of pores and some small cracks were distributed on the surface of the film.With the increase of electrolyte concentration and temperature,the pores became larger and the film became rougher.The phase composition of MAO film was identified to be?-Al₂O₃,?-Al₂O₃ and mullite(Al₆Si₂O₁₃)by X-Ray Diffraction technology.The results of hardness test showed that,the maximum hardness of the dense layer of the oxide film was 258.57HV,which was higher than the hardness of loose layer,and also much higher than that of the matrix.The average hardness and elastic modulus of the MAO film measured by nano-indentor are 0.069GPa and 2.17GPa respectively.When the temperature and electrolyte concentration both increased,the wear resistance and corrosion resistance of MAO film would decrease.The wear resistance and corrosion resistance of the film were better when the temperature was 10?and the concentration of Na₂Si O₃was 0.09mol/L.The growth kinetics curve of Si C_p/6092 aluminum matrix composite MAO film followed the law of parabola.The film grew rapidly at the beginning of oxidation,and slows down gradually after twenty minutes.In the oxidation process,the fiber-like?-Al₂O₃ on the surface of the film decreased gradually with the surface roughness increased.After oxidation for sixty minutes,the film grew more to the outside of the substrate and less inward.The lower temperature and lower Na₂Si O₃ concentration would increase the inward growth ratio of the film and improve its wear resistance and corrosion resistance.