The present study reports, for the first time, the highly efficient formation of barrier-type anodic films, with flat and parallel metal/film and film/electrolyte interfaces, on magnesium in ethylene glycol electrolytes containing ammonium fluoride and water. The anodizing voltage increases linearly with time during galvanostatic anodizing at 10 A m -2 up to 350 V.The anodic film formed to 200 V is 247 nm thick, containing a crystalline MgF 2 phase.Analysis by Rutherford backscattering spectroscopy discloses the film composition of MgF 1.8 O 0.1 and Pilling-Bedworth ratio (PBR) of 1.67. The PBR value greater than unity and the formation of chemically stable fluoride-based films may contribute to the film growth at high current efficiency.

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The pitting corrosion behavior of high purity aluminum covered with barrier-type anodic films, which are formed in neutral borate and phosphate electrolytes, has been examined in 0.5 mol dm -3 NaCl solution at an applied potential of -0.6 V vs Ag/AgCl, which is slightly nobler than the pitting potential of -0.64 V in the same solution. The pitting current density, i p , increased with time after an incubation time, t i . The double logarithmic plot of i p and polarization time, t, reveals two straight lines, which are separated at the time, . The slope becomes larger after  for the specimens anodized in the phosphate electrolyte, while it becomes smaller for those in the borate electrolyte.Both the t i and τ increase with the thickness of the anodic films, and at the similar film thickness they are much larger for the anodic films formed in the phosphate electrolyte than for those in the borate electrolyte. The corrosion process can be divided into three stages; the incubation period up to t i , the pit nucleation period before  and the pit growth period after . We have discussed the different pitting corrosion behavior of the aluminum specimens covered with the anodic films formed in the borate and phosphate electrolytes in terms of ion selectivity of the anodic films.