Cailiao Baohu (Oct 2024)
Study on the Preparation and Corrosion Resistance of Cerium-Based Chemical Conversion Coating on 2198 Al-Li Alloy
Abstract
The 2198 aluminum-lithium alloy exhibits a high specific strength and specific stiffness， making it widely applicable in the aerospace sector.However， it is highly sensitive to localized corrosion， necessitating appropriate surface treatments to enhance its corrosion resistance.Rare earth chemical conversion coatings on 2198 Al-Li alloy were obtained by immersing the alloy in a solution of 0.02 mol/L CeCl3 and 0.029 mol/L H2O2 using chemical immersion method for 20 and 60 min.The morphology and composition of the rare earth chemical conversion coatings were observed and analyzed using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS).The elemental valence states of the conversion coatings were analyzed using X-ray photoelectron spectroscopy (XPS).The corrosion behavior and corrosion resistance mechanism of the rare earth chemical conversion coatings in a 0.1 mol/L NaCl solution were studied through potentiodynamic polarization curves， electrochemical impedance spectroscopy (EIS)， and Mott-Schottky (M-S) curves.Results showed that the rare earth chemical conversion coating on the 2198 Al-Li alloy was composed of Ce4＋and Ce3＋hydroxides and oxides， Al3＋oxide， and a small amount of Cu element， with all elements uniformly distributed on the surface.From the surface to the interior of the rare earth chemical conversion coating， the metal hydroxides decreased and the metal oxides increased.The thickness of the rare earth chemical conversion coatings obtained after 20 min and 60 min of immersion was about 0.81 μm and 1.50 μm， respectively.In the 0.1 mol/L NaCl solution， the rare earth chemical conversion coatings on the 2198 Al-Li alloy could inhibit the cathodic oxygen absorption process， reduce the corrosion current density， and improve the corrosion resistance of this alloy.Compared with the rare earth chemical conversion coating from 20 min of immersion， the coating from 60 min of immersion exhibited higher corrosion resistance.At the same time， the rare earth chemical conversion treatment altered the corrosion mechanism of the alloy，resulting in the disappearance of the impedance arc related to Cl- adsorption.This was attributed to the reduced carrier density in the rare earth chemical conversion coating，which exhibited n-type semiconductor characteristics；the positive charge of the carrier density hindered the adsorption of Cl-.
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