The Preparation And Corrosion Resistant Of Micro-Arc Oxide Coatings On Aluminium Alloy

In this paper, the purpose was that aluminium alloy corrosion resistant was improved, using micro-arc oxidation (MAO) technology on aluminum alloy (LY12) in situ growth of the ceramic layer.Preparation for ceramic process,the corrosion resistant effect on processing parameters were studied.The parameters contain voltage increasing speed,voltage,time,electrolyte concentration.Effects of initial temperature, additament sodium dodecyl benzene sulfonate and sodium dodecyl sulfate on the corrosion resistant, phase composition, surface morphology and roughness of ceramic coating on aluminium alloy were studied.The corrosion resistant of the coating was tested in electrochemical analyzer;The phase composition and residual stresses of the coating were investigated by X-ray diffraction;The surface morphology was analyzed using SEM and metallography microscope.The surface roughness was tested in surface profilers.An optimized processing parameters which could fast prepare a high quality ceramic coating using MAO on aluminum alloy LY12 were obtained as follows: voltage increasing speed 8.5 V/s, final voltage 323 V, NaOH 2 g/L, NaAlO₂ 10 g/L, time 45 minute, initial temperature 50℃.On the condition of constant voltage,stresses on the coatings was compressive stresses.With the increasing of oxidation time ,residual stresses and coating thickness increase linearity in the first 30 minutes ,residual stresses was maximum at 30 minute which reached -643 MPa.Because micro-crack released part of residual stresses,residual stresses reduced to -101 MPa at 60 minute. Additament improved the corrosion resistance of ceramic coating. The best corrosion resistant was obtained while odium dodecyl benzene sulfonate was 0.08g/L or sodium dodecyl sulfate was 0.03g/L. Ceramic coating containedγ-Al₂O₃ andα-Al₂O₃,50℃electrolyte or adding additament decreased all surface roughness,porosity,hole depth and 50℃ electrolyte improved theα-Al₂O₃ content.