| For aluminum and its alloys chromate passivation treatment was most common method of surface treatment, but the Cr(VI) has large toxic and pollution to the environment seriously, the used of Cr(VI) has been banned or restricted in many industries, in order to replace the traditional chromate passivation process a series of green metal passivation has been developed. The titanium-zirconium passivation technology has been used in the industrial production. This article reported that the colorless Ti-Zr conversion coating was prepared in AA6061. The formation and performance of the Ti-Zr conversion coating on AA6061were studied in this article.Preparations of titanium-zirconium conversion coating conditions were concluded with single-factor test and orthogonal test. The best preparation of Ti-Zr conversion coating was:50mass%H2TiF61.7g·L-1,45mass%H2ZrF60.5g·L-1, the additive A was0.25g·L-1, pH=4.0, reaction120s at30oC and dried for30min at60oC. The electrochemical analysis showed that the Icorr decreased form5.63?A·cm-2(bare) to1.518?A·cm-2(Ti-Zr conversion coating) mean that the Ti-Zr conversion coatings can improve the corrosion resistance of the AA6061. The salt spry test was used to study corrosion resistance of Ti-Zr film. The results showed that after168h salt spray test only2%were corroded in the surface of AA6061. Testing showed that the Ti-Zr conversion coating provided improved adhesion relative to bare aluminum alloy. However, the Ti-Zr conversion coating was somewhat gap to commercial product. The Ti-Zr conversion coating morphology and the main component of the conversion coating were investigated by means of SEM and EDX. It showed that the conversion coating was composed of Al, Ti, Zr, F and O elements. It was observed that during passivation treatmen due to oxygen reduction and hydrogen evolution reactions the alkaline diffusion layer developed around the-Al(Fe,Mn)Si particles, the Ti-Zr conversion coating was formed throughout the surface of the AA6061. It was observed that the Ti-Zr conversion coating is very thin (<0.3?m).To improve the corrosion resistance and binding force with paint, the silane film was prepared on the surface of the Ti-Zr conversion coating. Through the study to TEOS, KH-550, KH-570and H four different silane it found that the H was the best. The electrochemical analysis was used to study the factors that influence corrosion resistance of the composite film. The best process for H composite film was:H:2vol%, V(alcohol)/V(H2O)=5/95, hydrolysis time for more than12h, the pH was adjusted by NH3·H2O or CH3COOH to4.0. The AA6061which was treatment by Ti-Zr passivation solution was immersed at30oC for10min, and dry30min at100oC. By infrared and other testing methods show that the silane film was mainly composed-Si-O-Si-cross-linked structure in the surfaces of the Ti-Zr conversion coating, and the film could hinder the corrosive media further contact to the matrix. The corrosion resistance of the6061aluminum alloy was improved by the silan film. The neutral salt spray test was used to study the corrosion resistance of composite film. After500h neutral salt spray test no corrosion were found on the surface of the samples. Studies have shown that the composite film with H can further enhanced binding force between the substrate and the paint. Testing showed that composite film based pre-treatment provided improved adhesion relative to Ti-Zr conversion coating. The samples with the composite film paint after1008h neutral salt spray test and5mass%NaCl immersion, the entire coating system with no significant difference compared to commercial products with organically sealed. The paint adhesion reaches to0level. |
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