Figure summarizes surface optical microscopy images labeling the characteristic surface areas where Raman spectra shown in Fig. were recorded. Optical images also give a difference in the visual appearance and color of the surface due to the deposition of Mn-rich layers. confirmed the presence of Mn-rich surface precipitates on all examined alloys. In all examined conditions Raman spectra showed very similar features. Raman bands at 278, 494, 582, and 632 cm - 1 were identified as a signal from γ-MnO2 oxide . The high intensity of these peaks supports that Mn(IV) species predominate in the composition of the surface films and that the inhibition mechanism is oxidative-reductive. At the same time, Raman bands of much lower intensity at 359 and 389 cm -1 recorded after 1 h of exposure can be assigned to hydrated MnOOH . These bands were absent after prolonged 24 h experiments. Finally, two Raman bands at 443 and 1094 cm -1 seen in some conditions were identified as a signal from magnesium hydroxide and magnesium and/or lithium carbonate, respectively . Note that the Raman band at 278 cm -1 can be also assigned to a thin surface layers of MgO/Mg(OH)2 . It should be noted that no prominent signal of Mn(VII) species was observed during the Raman measurements, suggesting that the initial species do not play a decisive role in the inhibition mechanism and the reduction of permanganate ions is required to initiate the formation of the Mn-rich surface films.