Protection by Thermal and Chemical Activation with Cerium Salts of the Alloy AA2017 in Aqueous Solutions of NaCl
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THE aluminum-copper alloys are widely employed in the aeronautical industry for numerous structural components because of their excellent ratios of weight to mechanical properties. Nevertheless, these alloys present serious problems of localized corrosion, especially in media that contain chlorides, principally because of the heterogeneous microstructure of the alloy. This behavior against corrosion in the aggressive medium must be analyzed and characterized for the subsequent design of appropriate systems of protection. In a first article, we describe a study of the corrosion mechanism of the Al-Cu alloy AA2017-T3 in a solution of NaCl.[1] The results obtained demonstrated that the intermetallics present in the alloy AA2017 are responsible for its behavior in a medium with a high concentration of MANUEL BETHENCOURT, Lecturer, is with the Departamento de Ciencia de los Materiales e Ingenierı´ a y Quı´ mica Inorga´nica, Centro Andaluz de Ciencia y Tecnologı´ a Marinas, Universidad de Ca´diz, Polı´ gono Rı´ o San Pedro s/n, 11510-Puerto Real, Ca´diz, Spain. Contact e-mail: [email protected] FRANCISCO JAVIER BOTANA, Professor, and LEANDRO GONZA´LEZ-ROVIRA, Researcher, are with the Departamento de Ciencia de los Materiales e Ingenierı´ a y Quı´ mica Inorga´nica, Facultad de Ciencias del Mar, Universidad de Ca´diz. MARI´A JOSE´ CANO, Lecturer, is with the Departamento de Ingenierı´ a Civil, de Materiales y Fabricacio´n, Escuela Te´cnica Superior de Ingenierı´ a Industrial, Univerisad de Ma´laga, 29071-Ma´laga, Spain. MARIANO MARCOS, Lecturer, is with the Departamento de Ingenierı´ a Meca´nica, Escuela Superior de Ingenierı´ a, Universidad de Ca´diz, C/Chile s/n, 11003-Ca´diz, Spain. JOSE´ MARI´A SA´NCHEZ-AMAYA, Researcher, is with TITANIA, Ensayos y Proyectos Industriales, S.L.U. Parque Tecnolo´gico TecnoBahı´ a Edif. RETSE Nave 4. Ctra. Sanlu´car Km 7, 11500-El Puerto de Santa Marı´ a, Spain. Manuscript submitted April 11, 2011. Article published online August 30, 2011 182—VOLUME 43A, JANUARY 2012
chlorides. It has been observed that the Al(Cu,Mg) intermetallics initially present an anodic behavior with respect to the matrix, giving rise to a process of selective dealloying of Mg and Al. As a result, there is an increase in the concentration of Cu in these intermetallics, which is the cause of their subsequent cathodic behavior. The process of reduction of oxygen to OH- takes place as the cathodic response. The local increase of the pH causes the dissolution of the layer of oxide and of the neighboring aluminum. In contrast, the Al(Cu,Fe,Mn) intermetallics display a cathodic behavior with respect to the matrix, and an oxygen reduction reaction takes place over these. The associated anodic response is the oxidation of the matrix. At the same time, the local increase of the pH produces the dissolution of the layer of oxide and of the matrix that surrounds these intermetallics. Similar results were obtained by Buchheit et al.[2] and Dimitrov et al.[3] in aluminum alloy 2024. Having identified the behavior of the inte
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