Preparation Of Plasma Electrolytic Oxide Layer Of Copper Alloy And Its Hydrophobic Properties

Copper has a face-centered cubic crystal structure,which is easy to process and shape,and has high electrical and thermal conductivity.It is widely used in aerospace,electronics and electrical appliances,marine vessels,machinery and instruments,transportation,information and communication industries.However,the polarization corrosion that exists during use seriously affects the service performance of copper and copper alloy equipment.In contrast,most failures of copper and copper alloys occur on the surface of the metal and do not have a direct effect on its internal organization.Therefore,the preparation of surfaces with low wettability,especially hydrophobic surfaces,on metal substrates can confer good corrosion resistance to copper and copper alloys,which has high application value and market prospect.Under the conventional theory,suitable micro and nano rough structures and low surface energy chemicals are indispensable factors to build and maintain the hydrophobic properties of material surfaces.However,the microscopic rough structure of most hydrophobic surfaces has a low mechanical stability.Under external loads,the surface rough structure is highly susceptible to wear,resulting in failure of the hydrophobic properties.To address this problem,a method combining plasma electrolytic oxidation and hydrophobic coating is proposed in this paper,and a plasma electrolytic oxidation composite ceramic film layer with hydrophobic and corrosion-resistant properties is successfully prepared on the surface of brass.The main study contents and key findings are as follows:（1）Preparation of plasma electrolytic oxide film layer on the surface of H62 brass.The electrolyte is formulated with Na₂SiO₃·9H₂O as the main component and supplemented with a small amount of sodium hydroxide Na OH to make the electrolyte PH value in the range of 11.7-12.3.The concentration of Na₂SiO₃·9H₂O in the electrolyte was varied and the effect of Na₂SiO₃·9H₂O concentration on the thickness,surface microscopic morphology,roughness,chemical components,phase composition,bonding force and corrosion resistance of the plasma electrolytic oxide film was analyzed.The results show that the film layers are in the form of metal oxides of Cu,Zn,O,Sielements and amorphous silica.The higher the concentration of Na₂SiO₃·9H₂O,the higher the number of micropores and the more uniform the size and distribution of pores on the surface of the film layer,while the thickness of the film layer increases and then decreases,and the surface roughness value decreases and then increases.However,with too large Na₂SiO₃·9H₂O concentration,the plasma electrolytic oxidation reaction intensifies and the film quality decreases rather than rises.When the concentration of Na₂SiO₃·9H₂O was 8g/L,the film bonding and corrosion resistance were the best,and the self-corrosion current density decreased by 2 orders of magnitude compared with that of the substrate.（2）Preparation of Na₂WO₄doped plasma electrolytic oxide film layers.A small amount of Na₂WO₄passivator was added to the Na₂SiO₃·9H₂O electrolyte and the plasma electrolytic oxidation of H62 brass was carried out using the same electrical parameters as in the previous section.The effect of Na₂WO₄concentration on the thickness,surface morphology,surface roughness,chemical composition,phase composition,and corrosion resistance of the plasma electrolytic oxide film layer was also analyzed.It was found that the oxide film layer after Na₂WO₄doping was mainly composed of Cu,Zn,O,Siand W.Cuand Znwere derived from the brass matrix,and O,Siand W were derived from the electrolyte.The increase of Na₂WO₄concentration leads to the gradual increase of Ra value of the film layer,while the thickness of the film layer tends to increase first and then decrease.When the concentration of Na₂WO₄is 1 g/L,the plasma electrolytic oxide layer has the best corrosion resistance with a low self-corrosion current density of 1.026×10^-4A/cm².It can be seen that the doping of Na₂WO₄can significantly improve the surface morphology and corrosion resistance of the oxide film layer.（3）Preparation of hydrophobic and corrosion-resistant composite film layers based on plasma electrolytic oxidation.The Na₂WO₄doped plasma electrolytic oxidation samples were immersed in a stearic acid-ethanol mixture for hydrophobic modification treatment,and the length of sample immersion time was controlled,and the surface micromorphology,wettability,composition,and corrosion resistance of the composite film layer were analyzed.It was found that after the plasma electrolytic oxidation of H62 brass samples soaked in stearic acid,the micro-pores and micro-cracks on the surface of the film were covered by"coral"like micro-nano-rough structures.The chemical components of the film surface are Cu,Zn,Si,O,W and the element C.The physical phase composition of the film layer is CuO,ZnO,SiO₂,Cu₂O and WO₃.With the extension of soaking time,the corrosion resistance,hydrophobicity and self-cleaning properties of the composite film layer surface are significantly improved.When the immersion time was 48 h,the static contact angle of water droplets on the surface of the composite film layer reached 158°,and the self-corrosion current density was as low as 6.788×10^-5A/cm².