Study On Silanization Of Anodized Film On Al Alloy

Aluminum anodic oxidation is a technique which can be in-situ grown an oxide film with the protection, decoration and other functions on the surface of aluminum alloy. Not only the surface hardness and wear resistance of aluminum alloy were greatly improved, but also its corrosion resistance increased with the oxide film, which greatly expanded the application scope of aluminum alloy. But the dissolution of anode oxidation film appeared during the growth of anodic oxidation film due to the limit of growth mechanism of anodic oxidation,the porous structure film formed at last which limited the corrosion protection of the film, the sealing process of anodic oxide film usually used to solve this problem during industrial production. In order to solve this problem, according to the structural and component characteristics of anodic oxide film, a new method of sealing process put forward in this paper:using the silanization treatment to seal the pores of the aluminum alloy anodic oxidation film,in order to obtain more effective and environmental method than the traditional sealed method for anodic oxide film.6061 aluminum alloy were used as the substrate material in this study. At first, the feasibility of silanization treatment on aluminum alloy anodic oxidation film were explored,the results show that the corrosion resistance of anodic oxide film can be improved significantly by silanization treatment; Then the hydroxylation pretreatment was applied to anodic oxide film according to the composition characteristic of anode oxidation and mechanism of silanization, that is, the surface of anodic oxidation film is rich in hydroxyl compounds through hydroxylation pretreatment, which facilitate the silicon alkylation process and promote the formation of silane film. The results show that the appropriate hydroxylation pretreatment can further enhance the effect of silanization treatment and improve the corrosion resistance of films significantly. Three methods of hydroxylation pretreatment the hydrothermal method, alkaline solution processing method and precast of layered double hydroxide method were explored for anode oxidation film, and the influence of hydrothermal pretreatment of the silicon alkylation process on oxide film were studied emphatically in this study.The change of the surface composition of anode oxidation film was obtained by infrared spectrum (IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) before and after the pretreatment; The morphology of anode oxidation films after the different sealing methods was investigated by using a SEM; The corrosion resistance of anodic oxide film by hydroxylation pretreatment after silanization treatment was investigated by potentiodynamic polarization curves, weightlessness experiment, contact angle test, salt spray test; The corrosion behavior of anodic oxide film with different sealing treatment was studied by electrochemical impedance spectroscopy. The results show that:The main components of anodic oxide film is amorphous Al2O3,a small amount of AlOOH and Al(OH)3 also contains at next,hydroxyl compounds is rich in AlOOH which is to ensure the foundation of the silanization treatment of the anode oxidation film. After silanization treatment, the hydrophobic of the anodic oxidation film increased and the corrosion resistance had more obvious improvement. But the condensation reaction between silanols has been constrained due to the insufficient amount of hydroxyl on the surface of anodic oxide film, leading to the pores and defects of anodic oxide film not completely sealed.Hydrothermal method is an effective hydroxylation pretreatment method for anodic oxidation film, which can significantly enhance the effect of silanization on oxidation film and enhance the corrosion resistance of the film significantly. During the formation of hydroxyl compounds on the surface of the anodic oxide films in this method, the products of hydrothermal method have the effect to seal the pores of the anodic oxidation film at the same time, that is, it has a dual effect for the corrosion resistance of the films. Hydrothermal temperature and time of the pretreatment process parameters have significant influence on the hydroxylation degree of the surface of oxide film, such as hydroxylation degree has significant influence,the main components of anodic oxide film change to AlOOH by hydrothermal treatment under the 90 ℃for 30 min, the existence of a large number of hydroxyl compounds enhanced the effect of silanization significantly. The research also found that the coordination forms of Al-0 on the surface of anodic oxide film have important influence on the effect of silanization treatment.During the hydroxylation pretreatment of anodic oxide film by alkaline solution, the processing parameters such as solution composition and pH value, processing temperature and time had a greater influence on the effect of treating, the unsuitable technology lead to the anode oxidation been damaged, unable to achieve their purpose. Solution composition and technological parameters is needed further research.Through the precast of layered double hydroxide method can also achieve the purpose of hydroxylation surface of the anode oxidation film,thus increased the effect of silanization significantly, further enhance the oxidation film corrosion resistance. However this method is only applicable to the low temperature short curing of silanization pretreatment affect by the heat resistance of the layered double hydroxide. It is difficult to obvious advantages compared with hydrothermal method.