Formation And Characterization Of Ti-Zr Based Conversion Coatings On Ally Aluminum

In this thesis, a colored Ti-Zr conversion coating process has been developed on thesurface of alloy aluminum at room temperature，with potassium fluozirconate，tetrabutyltitanate，tannic acid，magnesium sulfate and sodium fluoride as film forming material，The coating preparation process was optimized through orthogonal experiments. Based onthis，a colored Ti conversion coating and a colored Zr conversion coating have beendeveloped. the influence of these variables(treatment temperature，time，bath pH，andconcentrations of various film forming material)on the anti-corrosion performance ofconversion coatings was investigated using single factor experiments.The anti-corrosion performance, adhesion, surface morphology, composition of theconversion coatings were investigated by dropping test, electrochemical workstation,coating adhesion test,，SEM,，AFM， surface profiler， XRD， XPS， FT-IR and othermeans of measurements.The optimum parameters to prepare colored Ti-Zr conversion coating are determinedby the orthogonal test. The results are tannic acid1.00g/L, potassium fluorozirconate0.75g/L, sodium fluoride1.25g/L, magnesium sulfate1.0g/L, tetrabutyl titanate0.08g/L，treatment temperature of25℃～30℃and treatment time of10min.Pale yellow Ti-Zr conversion coating and Ti conversion coating and white Zrconversion coating have been developed. on aluminum alloy surface. The impedancevalue of conversion treated aluminum alloy is higher than that of untreated aluminumalloy by one order of magnitude, and the corrosion current density decreases by two ordersof magnitude. The electrochemical results indicate that, The conversion coatings canprevent corrosion medium from penetrating aluminum alloy and further suppress theanodic reaction of alloy aluminum, thus improve the anti-corrosion performance of alloyaluminum efficiently..The analysis by SEM and AFM shows that, the colored even and continuousconversion coatings which formed on alloy aluminum surface are composed of spherodalparticles which has characteristic of equal particle size. but the surface morphology of Zr conversion coating is rougher than others. XRD and XPS test results show that, thecrystalline structure of the three kinds of conversion coating is resemble, C、O、Al、Ti、Zr、F etc elements were contained in the conversion coatings. Conversion coatingsmainly contain some metal oxides and organic complex. FT-IR test results indicate that,due to the introduction of tannic acid and tetrabutyl titanate into the conversion solution,hydroxyl radical, benzene ring, carbanyl group and methylene were contained in theconversion coatings, The existence of these groups enhanced the adhesion of conversioncoating.