SRET measurements showed that under

SRET measurements showed that under anodic polarization 100 mV above Escr the Al–La alloy devel- oped selective dissolution. Measurements at Escr as well as 50 mV below Escr did not show localized activity. The line scans illustrated in Figure 4 correspond to SRET measurements performed after 10, 30 and 50 min of polarization at 100 mV above Escr.The graphic in Figure 4 presents the electrochemical activity in terms of the ohmic potential gradients in the electrolyte surrounding the sites developing localized dissolution. As seen in Figure 4, the electrochemical activity changes with time. In some cases the localized activity observed vanished completely in some sites and new sites appeared in different positions. The signal measured by the SRET is not directly related to the size of the local anodes; however, it is related to their electro- chemical activity. With the SRET it was possible to demonstrate that at potential levels below Escr the alloy dissolves actively with some sites developing incipient localized attack (low electrochemical activity), which after a few seconds disappeared completely. The local- ized activity increased substantially at potentials 100 mV above Escr and broadened with polarization time as new very active local anodes came into view. The behaviour observed for the Al–12.6 wt.%La alloy indicates that the presence of La inhibits the formation of a passive layer but does not make the alloy active. Anodic polarization at potentials levels above Escr facil- itated selective dissolution.