Aluminum Alloy Pretreatment And Characterizationof No Chrone Conversion Coatings On Ally Aluminum

This paper is focused on the research of pretreatment for the surface of aluminum alloy and the formation of the chromium-free conversion film. In this experiment, nitric acid, activators(Na HF2) and etchant(Fe(NO3)3) are used as the material of pretreatment agent. In the next step, by observing the effect of this experiment, we can creat a high-value pretreatment agent. The ricipe of this pretreatment agent is as following introduction: concentrated nitric acid(35%), 5g/LNa HF2, 100g/LFe(NO3)3.Secondly, this article analyzed the formation of free-chrome conversion film on aluminum alloy and the formation of free-chromium conversion film by activator of Na F, oxidant H2O2 and other liquid at room temperature. Then according to the single factor experiment, it works on the corrosion resistance of conversion film affected by various factors, such as temperature, p H, activator Na F, oxidant H2O2 and other factors like the conversion of liquid and auxiliary salt.By analysis test means,such as Neutral salt spray test, electrochemical workstation, scanning electron microscope(SEM), X-ray diffraction(XRD), the chemical corrosion resistance of conversion film surface morphology and composition structure are tested and characterized. The conversion coating preparation technology research results show that the optimum process conditions are: auxiliary salt 50 mg/L, Na F5g/L, H2O21 m L/L, solution p H value, reaction temperature and conversion time were 4.0, 20 ℃, 7 min.The experiments indicates that its film is uniformity and has no obvious surface defects, and the base has a good binding ability. As to the corrosin resistence, the chromium-free conversion film which was texted for nearly 10 hours is better than the aluminum alloy which was text in the salt spray for 2 hours. Scanning electron microscope(SEM) images shows the preparation of conversion coating is a process of growing up of nucleation and crystal. Based on the SEM images, the research finds that the conversion film is covering on the surface of aluminum alloy steadly and completedly and the particles of different sizes adhesion on the surface of the substrate can be observed. By electrochemical tests, it shows that the resistence value of aluminum alloywhich was conversed is 2 orders higher than the blank one. In this way, it can effectively prevent corrosion getting into the aluminum alloy base, so as to effectively improve the corrosion resistance of aluminum alloy.At last,this paper presents a short introduction of the production of wheel and maintenance cycle. And by doing a further research, this technology can be applied in the real production and maintenance cycle.