analysis. The presence of C is attributable to ambient
contamination. The peak of Mg2s binding energy of
89.1 eV and the peak of Mg2p binding energy of 50.4 eV
were assigned to the presence of MgO [25, 26]. The peak
of Na1s binding energy of 1071.6 eV was attributed to the
NaF compound [26] and the peaks of P2s and P2p binding
energy 191.0 and 133.9 eV, respectively, were associated
to the presence of Mg3(PO4)2 [32]. The presence of NaF is
probably due to the adsorption effect on the surface, in
agreement with EDS and XRD analysis.
3.1 Corrosion behaviour
To study the corrosion properties of the layers produced by
the PEO process, potentiodynamic anodic polarization and
EIS test were performed in a solution containing both
sulphates and chlorides (0.1 M Na2SO4 and 0.05 M NaCl).
3.1.1 Potentiodynamic polarization tests
The anodic polarization plots for commercially pure
magnesium treated with different current densities for 60 s are reported in Fig. 10a and the corrosion current densities
icorr and corrosion potentials Ecorr for the different treatments
are reported in Table 4. The corrosion resistance of
the PEO treated samples was significantly improved compared
with the untreated one. As a matter of fact, a
decrease in the current density and an increase in the corrosion
potential were observed. In particular, the untreated
sample and the one treated at 0.45 A cm-2
, the decrease of
icorr was higher than one order of magnitude. In terms of
corrosion potential, in comparison with the untreated
sampled, there was a slight decrease for the sample treated
at 0.1 A cm-2
, whereas an increase for all the other treated
samples was registered, with ennoblement of 0.14 V for the
sample treated at 0.45 A cm-2
. The better corrosion
properties of the samples treated with higher current densities
can be directly colligated with the thicker layer and
the reduction of the porosity on the surface, that both were
previously observed by SEM for high current densities
applied in the treatment.
The anodic polarization plot and the resulting data for
AM50 alloy treated at different current densities for 60 s
are reported in Fig. 10b and Table 4. Also for this alloy the