Modification Of 8-hydroxyquinoline On The Corrosion Resistance Of V/Zr Conversion Coating On LY12 Al Alloy

Because of having superior performances such as high strength, low density and great heat transfer and excellent electric conduction properties. LY12 is widely used in the aerospace, transportation, power electronic and many other fields. However, due to the effect of intermetallics Cu Al2 and Al2 Cu Mg, LY12 Al alloy is most easily corroded among all Al alloys so that its industrial application is greatly limited. Traditional chromate conversion coating has good corrosion resistance, but Cr( Ⅵ) has high carcinogenic, bioaccumulation and persistent diffusivity. Therefore, Cr(VI) was limited to use in the metal surface treatment by the European Union Ro HS Directive as early as 2003 and the first 12 th five year plan of our country in 2011―“Heavy metal pollution comprehensive prevention and control 12 th five year plan”. Therefore, a new alternative to chromate conversion treatment technology is urgently needed.In order to further improve the corrosion resistance of V/Zr inorganic conversion coating developed by our research group, this paper researched the inorganic/organic composite conversion coating on LY12 Al alloy. The research results, screening from the neutral salt spray corrosion resistance of V/Zr conversion coating on LY12 Al alloy modified by organic film formation agents-- glycine, tannic acid, benzotriazole,aluminum reagent and 8-hydroxyquinoline, showed that the modification effect of8-hydroxyquinoline was the best. The preparation conditions of coating were as follows: 8-hydroxyquinoline 0.1g/L, Na VO3 4.0g/L, K2 Zr F6 2.5g/L, p H 4.0, 70℃and35 minutes.The analysis results of scanning electron microscopy(SEM) and energy dispersive spectrometer(EDS) showed that the composite conversion coating modified by 8-hydroxyquinoline was the amorphous structure, mainly composed of C, O, F, Mg,Al, Cu and other elements. The further analysis results of X-ray photoelectron spectroscopy(XPS), fourier transform infrared spectrum(FTIR) showed that the surface of conversion coating was composed of V、Zr、N、O, the characteristic peak of N-H and O-H of 8-hydroxyquinoline. The composite thin film consisted of the inorganic conversion coating which contained the effective anti-corrosion components V2O5、Zr O2, and the organic conversion coating which was made of the complex of aluminum 8-hydroxyquinoline. Especially, 8-hydroxyquinoline content was the largest on copper intermetallics surface. It made the salt spray time of V/Zr conversion coating on LY12 Al alloy modified by 8-hydroxyquinoline increase from 24 h before modification to 96 h after modification, the corrosion potential of the sample increase by 36 m V, the corrosion current density reduce by 79.7%. Therefore, the corrosion resistance of LY12 Al alloy was greatly improved.