The SRET operates by measurement the ohmic potential gradients in solution induced by ionic flux emanating from sites undergoing localized attack. The equipment used was a Uniscan instruments SRET model SR100 in which a cylindrical specimen (sealed tube or bar) is made the working electrode, immersed in the electrolyte and rotated at precise speeds in the range 5–250 rpm. The scanning probe arrangement utilized to measure potential gradients consists of two platinum tips configured as differential inputs to the measuring electronics in order to reduce the inherent noise. This probe is driven parallel to the axis of rotation of the specimen very close to the specimen surface. The scanning probe is positioned by the computer such that the nearer platinum tip is as close as possible [18,19]. For the present work the distance between the surface of the sample and the scanning probe platinum tip was 150 lm. Line scan SRET measurements were conducted over the entire specimen circumference (9.425 mm). The scanning probe was moved vertically using steps of 50 lm covering the total length of the Al–La specimen (5.0 mm). The measurements were carried out by plac- ing the scanning probe in a fixed position of the sample length where the highest localized activity was detected. The rotation rate applied to the specimen was 93 rpm.The working electrode was potentiostatically polar- ized using a conventional three electrode corrosion cell with reference (SCE) and auxiliary electrode (platinum mesh).