Abstract
Specimens of pure aluminum and 4 different Al-Fe alloys of varing iron content ranging from 0.32% to 1.45% were immersed in aerated 0.1 M NaCl solutions for periods up to more than 1000 h. Long-term behavior of corrosion potentials of the specimens were observed and analysed with divisions into three stages. The corrosion processes taking place in each stage are illustrated in terms of the polarization curves on the individual single phases of pure aluminum, intermetallic compounds, and iron redispersed around corrosion pits. Scanning electron micrographs of the corroded specimens at each stage support the illustrations as follows. At the first stage, the cathodic reduction of disolved oxygen on the surface of intermetallic compounds is responsible for the progress of corrosion. At the second stage, the cathodic reduction of oxygen is retarded by corrosion products of aluminum hydroxide attached on to the surface of the cathodes. And at the third stage, corrosion proceeds in the pits beneath the corrosion products with the cathodic reduction of water under the corrosion potential of a few hundreds millivolts less than that of the first stage.
