ELECTRODISSOLUTION STUDIES OF THREE ALUMINUM ALLOYS IN ACID, NEUTRAL AND ALKALINE SOLUTIONS

摘要

Although aluminum and its alloys are chemically reactive, they are resistant to corrosion in solutions of pH 4 to 9 whenever aggressive ions chloride, iodine, bromide are not present. The resistance is attributed to the presence of a protective thin oxide film. The aim of this paper is to study the electrochemical behavior of three aluminum alloys Al-Cu-Mg1.5-Si-Mn0.6; Al-Li_2-Cu_2-Zr-Mg and Al-Li_2-Ti-Zr-Cu_2 in three elaborated states. Electrodissolution and localized corrosion characteristics of these alloys have been investigated by adequate electrochemical techniques including impedance spectroscopy in the pH range of 4 to 9 in the absence and in the presence of chloride ions. Potentiodynamic polarization curves for three alloys in acid, neutral and alkaline solutions in the absence and in the presence of chloride ions show that the corrosion parameters of these alloys (OCP, ε_(CORR), R_p, i_(corr), ε_(pitt)) depend especially on the concentration of halide ions and of the pH values of solutions. Impedance spectra for all alloys were similar in shape. The appearance of two semicircles in the impedance diagram was common to all alloys electrodes. The high frequency semicircle corresponds to a capacitive loop and the low frequency semicircle corresponds to an inductive loop. The semicircle radii were dependent on the pH values of solution and of the chloride ions concentration. The high frequency capacitive loop is related to the dielectric properties of the surface film and the low frequency inductive loop is attributed to the relaxation of adsorbed chloride ions and local metal dissolution.