Photochemical Preparation And Corrosion Resistance Of ZrO₂ Sol-gel Sealing Layer On MAO Coating Of Aluminum And Magnesium Alloy

Aluminum alloys and magnesium alloys are the widely used metals in the world due to their advantages of low density,high specific strength.high specific stiffness and good machinability.However,aluminum alloys and magnesium alloys have active chemical properties and poor corrosion resistance,which limit their service life and application in light-weight fields such as militay industry,aerospace and aviation.Micro-arc oxidation(MAO)technology was used to grow a ceramic coating on the surface of aluminum and magnesium alloy,which can significantly improve the corrosion resistance of the alloy.However,the MAO coating is loose and porous,providing a reaction channel for t.he corrosion medium and limiting the further improvement of the corrosion resistance.ZrO2:precursor solution has good fluidity and film-forming property and is widely used in sealing MAO coating.Traditional gel films are formed under high temperature conditions,wasting resources and failing to obtain dense sealing films.In this paper,a unique deep ultraviolet irradiation technology is used to study the preparation of compact and uniform ZrO2 sealing layer at low temperature.In this paper,the best process for preparing the ZrO2/MAO composite coating is obtained by comparing the corrosion resistance of samples obtained by different heat treatment temperatures and different ultraviolet irradiation times.In addition,the mechanism of ZrO2 sealing layer prepared by different processes was investigated by X-ray diffraction(XRD),scanning electron microscope(SEM),X-ray photoelectron diffraction(XPS),etc.The following conclusions are obtained:(1)ZrO2 layer effectively sealed the pores of MAO coating of aluminum and magnesium alloy and improve thire corrosion resistance.(2)When the annealing temperature of the ZrO2 sealed the MAO coating of aluminum alloy from 100℃ to 300℃,the ZrO2 sealing film becomes gradually flatter and denser.However with the increase of temperature,organic matter volatilizes rapidly,and the film cracks seriously,which leads to the decrease of corrosion resistance.When DUV process is adopted at 100,the O3 and O*generated by photochemical reaction make the organic matter oxidized into small molecule gas and slowly release out of the film,and thus obtaining compact and uniform ZrO2 film with significantly enhanced corrosion resistance.(3)Sealing treatment on MAO coating of magnesium alloy shows that compactness and corrosion resistance of the film increase with temperature from 100℃ to 275℃,Fureher increase the temperature to 425 ℃,corrosion resistance decreases.This is due to cracks formed at high temperature,resulting in electrolyte solution infiltration and electrochemical reaction.When DUV irradiation was introduced at 100 ℃,it was found that the longer the UV time,the denser and more uniform the sealing layer,and the higher the corrosion resistance of the sample.