Formation And Characterization Of Colourful Conversion Coatings On Aluminum Alloy

In this paper,we mainly studied the formulation and other properties of the color conversion film passivation solution prepared on the surface of aluminum alloy at room temperature.This paper mainly using cerium nitrate,two selenium oxide,tannic acid,the colored conversion film was prepared under certain conditions.Single factor experiments were used to study the effects of other factors,such as the concentration,temperature,time and pH on the corrosion resistance of the films.With dropping corrosion test,electrochemical workstation,scanning electron microscope?SEM?,atomic force microscopy?AFM?,X ray diffraction?XRD?,X ray photoelectron spectroscopy?XPS?and Fu Liye transform infrared spectrometer?FT-IR?,The corrosion resistance,adhesion,surface morphology and composition of the chemical conversion film were tested and characterized,In the film material,tannic acid,cerium nitrate,two selenium oxide is the main components of conversion film,NaF film and MgSO₄ is the film forming promoter.PH can affect the film formation rate,The conversion film with excellent corrosion resistance can be prepared at the temperature of 45? and the time of 10 min.Conversion coating preparation technology research results show that the tannic acid 1.25 g/L,NaF 1.25 g/L,cerium nitrate 1.25 g/L,SeO₂ 0.75 g/L,MgSO₄ 0.75 g/L,under the condition of 25 ?with 10 min,pH of 5,conversion coating of aluminum alloy surface uniform,continuous,with a dark red.Tafel polarization curve test Aluminum Alloy conversion film showed that Aluminum Alloy conversion film corrosion current density and the blank Aluminum Alloy specimen corrosion current density decreased by an order of magnitude,indicating Aluminum Alloy after conversion treatment after corrosion resistance has been improved;AC impedance test Aluminum Alloy conversion film show that the capacitive arc capacitive arc Aluminum Alloy conversion film is far greater than the Aluminum Alloy blank,that Aluminum Alloy conversion film polarization resistance is large,the corrosion resistance is improved;Through drop test can show alloy conversion coating and chromate conversion coating after dealing with the spot experiment of the average color time 41 sand 50 s,the corrosion resistance and corrosion resistance of the chromate conversion coating is close to that Aluminum Alloy conversion film.By the characterization of surface morphology of SEM conversion film.Results show that the Aluminum Alloy transformation of the film is smooth,uniform,continuous,dense,conversion film on the surface of micro concave convex phenomenon,containing spherical particles,which are beneficial to the increase of the morphology of Aluminum Alloy film and bond strength.Through FT-IR,XRD,the results showed that the structure,XPS means of conversion film,the main component for conversion film and metal ion chelate hydrolysis of tannic acid,followed by Na₃AlF₆,AlF₃·3H₂O and a small amount of CeO₂,Se,Al₂O₃.The aluminum alloy conversion film has good adhesion with the film,and the organic functional group in the conversion film is very important to improve the adhesion of the film.The conversion film on the surface of aluminum alloy is a highly heterogeneous system.Aluminum alloy conversion film is mainly Na₃AlF₆,AlF₃·3H₂O and a small amount of CeO₂,Se and complex organic compounds composed of two layers.