| Aluminum belongs to the amphoteric metal which has active chemical properties. Thealuminum surface will form a compact oxide film under natural conditions and the thicknessof the natural oxide film is a few nanometers to tens of nanometers. Due to the lowconductivity of the oxide film, it can prevent the cathode reaction. Although aluminum hasgood anti-corrosion property in atmosphere, the atmospheric temperature, salinity andimpurities species can impact on its corrosion resistance performance. The corrosion occurswhen the aluminum is placed in the aqueous solution containing chloride ions whose pHvalue is5~8and the corrosion rate accelerates with the increase of hydrogen ionsconcentration when placed in acidic aqueous solution. Galvanic corrosion, pitting corrosion,filiform corrosion, exfoliation corrosion, intergranular corrosion and stress corrosion arecommon corrosion morphologies of aluminum and aluminum alloys. In order to overcome thelack of performance, prolong its service and expand the range of application, it is necessary tocarry on the surface treatment to improve performance in protection and function aspects ofaluminum alloy.In this paper, organic and hard films have been prepared on the aluminum alloy surfacesuccessfully, the anti-corrosion and tribological properties of the films has been determined.The effects of the as-prepared films on properties of aluminum alloy and the mechanism hasbeen discussed.Firstly, combining micro/nano-hierarchical structures was constructed by a simple andversatile chemical etching method and further modification with n-octadecyltriethoxysilane(OTS), perfluorodecyltriethoxysilane (PFDS) and aminopropyltriethoxysilane (APS) tofabricate hydrophobic and hydrophilic films on aluminum alloy AA2024substrates. Thesurface morphology, surface composition and bonding structure information wascharacterized by SEM, AFM, FTIR and XPS and the influence on of surface morphology andfilm type on the wettability was investigated. The anti-corrosion capacities of the as-preparedfilms was studied by polarization curves and electrochemical impedance spectroscopy and the optimum parameters for fabricating films were determined: the volume fraction ofhydrochloric acid solution was33%, the chemical etching time was2min, samples modifiedby hydrophobic reagents own the bigget contact angle. The corrosion potential shiftedpositively0.45V and the corrosion current density decreased4times with respect to the barealuminum samples. The films improve the corrosion resistance properties of aluminum alloyeffectively. According to results of tribological tests: the OTS-SAMs owned the lowestcoefficient of friction and the wear rate decreased8orders of magnitude relative to barealuminum alloy.Secondly, micro/nano-structures were formed by chemical etching and anodicoxidation methods on the surface of aluminum alloy. Then, anodic oxidation films withexcellent anti-corrosion performance were obtained after being chemically modified via aself-assembly layer by dodecafluoroheptylpropyltrimethoxysilane (G502) to improvecorrosion resistance of aluminum alloy. Effects of early chemical etching on the structure andpropertied of anodic oxide film were investigated. The results showed that: the chemicaletching process changed the morphology and anti-corrosion capacity of anodic oxide film astemplates. The film possessed the greatest corrosion resistance performance when chemicaletching time was3min. The corrosion potential shifted positively0.15V and the corrosioncurrent density decreased an order of magnitude with respect to the bare aluminum samples.The films improve the corrosion resistance properties of aluminum alloy effectively.Finally, in order to improve corrosion resistance, tribological properties as well asmechanical performance of aluminum alloys, diamond-like carbon films doped with Cr(Cr-DLC) was deposited by a method of magnetron sputtering. The results showed that: theCr layer which was used as the intermediate could effectively solve the problem that coatingdropped from the substrate when the film was deposited on the surface of aluminum alloydirectly and increase the intensity of the combination of coatings and substrates.Electrochemical, tribological and hardness tests were conducted to investigate theanti-corrosion and mechanical properties of the as-prepared films. The results showed that thecorrosion potential of the samples deposited with Cr-DLC films shifted positively0.3V and the coefficient of frictiondiminished4times with respect to the bare aluminum samples.Meanwhile, the wear rate decreased3orders of magnitude and the hardness increased fourtimes relative to the bare aluminum samples. |
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