| Self-assembling technology researches on pure aluminum base material showed that phosphonic acid molecules can form stable adsoprtion film on its surface.This technology has been tried on aluminum alloy surface also and showed that,due to the surface heterogeneous micro structure,the distribution of phosphonic acid molecules on different micro-regions is not inhomogeneous,and then has a negative effect on the films' corrosion inhibition performance.So to investigate the adsorption behavior and distribution characteristics of phosphonic acid molecules on different micro-regions of 2024 alloy surface can help to understand defect mechanism of the membrane,and guide the design of corrosion inhibition film with high efficiency.In this paper,the micro-region distribution of phosphonic acid adsorption film on aluminum alloy surface and the film's defect mechanism were discussed by studying the adsorption behavior of phosphonic acid molecules on simulated alloy surfaces,combined with the qualitative and quantitative analysis for adsorption film by Auger spectroscopy technology.Then on this basis,the idea of constructing organic-inorganic composite film was proposed,and alkylphosphonic acid-cerium salt composite film was designed.The research results showed that composite modification can obviously improve the film's corrosion inhibition performance.The main research results are as following:1)The simulated AlCuMg segregation phase and simulated matrix alloy were prepared by powder metallurgy based on the micro-component panalysis of 2024 alloy.Research methodes including potentiodynamic scanning,Electrochemical Impedance Spectrum(EIS),open circuit potential(OCP),galvanic current testing and Scanning Electron Microscope(SEM)were used to study the adsorption behavior and corrosion inhibition performance of films on different sample surfaces.The results show that 1-tetradecylphosphonic acid(TDPA)can adsorb on all sample surfaces.The corrosion current of modified simulated matrix is reduced to the minimum value,and that of simulated segregation is still the biggest.These suggest that excellent corrosion inhibition film is more easily formed on matrix surface than on segregation surface.The galvanic couple test results indicate that,the protect for segregation surface is especially important,because segregation is the weak area of oxide film on the 2024 alloy surafce.As the galvanic anode region,the sufficient coverage and protection on its surface can restrain aggressive ions's first attack,and thereby inhibit local corrosion.2)The micro-region distribution of phosphonic acid film on 2024 alloy surface was studied by Auger Electron Spectroscopy(AES).The results of large scale analysis and micro-spot analysis show that TDPA can adsorb on all the type of micro regions.But the adsorption quantity on copper-rich phase is less than that of matrix,and the detected low copper content corresponds to the high P content,namely more dense TDPA adsorption.Based on the analysis of atomic percentage obained by depth sputtering data,a mixed adsorption model of monolayer,bilayer and trilayer was proposed.3)Single TDPA film,single cerium conversion coating and TDPA/cerium conversion composite film were prepared on aluminum alloy surface.Research methodes including electrochemical testing(potentiodynamic scanning?EIS)?SEM and Energy Dispersive Xay Spectrom(EDX)were used to study the adsorption behavior and corrosion inhibition performance of the three kinds of films on the alloy surface.The results show that compared with single TDPA film and single cerium conversion coating,the corrosion current of composite TDPA/cerium conversion film modified aluminum alloy is reduced to the minimum,and the electrochemical impedance value is greatly increased also.Under the same corrosion condition,the corrosion degree of composite film modified alloy is the lightest,these indicate that aluminum alloy covered with TDPA/cerium conversion composite film show maximum resistance to corrosion.The pre-deposited cerium conversion coating before TDPA-modification can give priority protection to segregation,and improve the the surface's hydrophilcity,then enhance the density of phosphonic acid molecule by providing more chance to form Al-O-P adsorption bonding.In addition,it can also fill the defects of alkylphosphonic acid film.So the synergistic effect of these two kinds of films on aluminum alloy surface improves the alloy's resistance capability to pitting and general corrosion. |
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