%0 Journal Article
%T Corrosion Behaviour of Heat-Treated Aluminum-Magnesium Alloy in Chloride and EXCO Environments
%A S. O. Adeosun
%A O. I. Sekunowo
%A S. A. Balogun
%A V. D. Obiekea
%J International Journal of Corrosion
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/927380
%X Machines designed to operate in marine environment are generally vulnerable to failure by corrosion. It is therefore imperative that the corrosion susceptibility of such facilities is evaluated with a view to establishing mechanism for its mitigation. In this study, the corrosion behaviour of as-cast and retrogression-reagion (RRA) specimens of aluminum alloy containing 0.4¨C2.0 percent magnesium additions in NaCl, FeCl3, and EXCO solutions was investigated. The corrosion simulation processes involved gravimetric and electrochemical techniques. Results show substantial inducement of Mg2Si precipitates at a relatively higher magnesium addition, 1.2¨C2.0 percent, giving rise to increased attack. This phenomenon is predicated on the nature of the Mg2Si crystals being anodic relative to the alloy matrix which easily dissolved under attack by chemical constituents. Formation of Mg2Si intermetallic without corresponding appropriate oxides like SiO2 and MgO, which protect the precipitates from galvanic coupling with the matrix, accentuates susceptibility to corrosion. 1. Introduction Aluminum and its alloys are widely used in industry because of their light weight, high strength, and good corrosion resistance which is due to the formation of a protective oxide layer. However, under saline conditions such as those encountered in marine environments, aluminum alloys are vulnerable to localised degradation in forms of pitting and crevice corrosion. This type of corrosion involves the adsorption of an anion in particular chloride ion, Cl-, at the oxide-solution interface. In conventional metallic materials, the strong oxidizing power of the environment is required to establish spontaneous passivity; hence, to be of practical use, metallic materials must exhibit significant level of passivity in a given environment. The passive stable surface film acts as a barrier for the transfer of cations from the metal to the environment and for the counter diffusion of oxygen and other anions. The air-formed film must be stable without damage to the underlying alloy surface in a given environment. Chemically homogenous, single-phase amorphous alloys free from crystalline defects such as precipitates, segregates, grain boundaries, and dislocations often create conducive environment for the formation of uniform passive film without any weak points [1]. Aluminum forms a protective oxide film in the pH range 4.0¨C8.5, but this depends on temperature, form of oxide present, and the presence of substances that form soluble complexes or insoluble salts with aluminum. This implies that
%U http://www.hindawi.com/journals/ijc/2012/927380/