1993 年 44 巻 9 号 p. 729-731
When aluminum specimens are cathodically polarized in a 1%NaCl solution whose pH has been ajusted to 1 by the addition of HCl, formation of pitting cavities over the aluminum surfaces is observed. It was found that the density of these cavities is considerably greater with aluminum specimens containing 273ppm of iron than with those containing only 1ppm. This is atributed to the presence in the former of finely dispersed intermetallic particles which provide preferential sites for the hydrogen evolution reactions during cathodic polarization. Due to the preferential reduction of protons and water, local pH around the particles increases during cathodic polarization and this, in turn, leads to local attack over the aluminum matrix surrounding the intermetallic particles and eventual formation of the pitting cavities.