Formation of barrier-type anodic films on ZE41 magnesium alloy in a fluoride/glycerol electrolyte

Barrier-type, nanocrystalline anodic films have been formed on a ZE41 magnesium alloy under a constant current density of 5 mA cm−2 in a glycerol/fluoride electrolyte, containing 5 vol.% of added water, at 293 K. The films contain magnesium, fluorine and oxygen as the major species, and lower amounts of alloying element species. The films grow at an efficiency of ∼0.8 to 0.9, with a formation ratio in the range of ∼1.2 to 1.4 nm V−1 at the matrix regions and with a ratio of ∼1.8 nm V−1 at Mg-Zn-RE second phase. At the former regions, rare earth species are enriched at the film surface and zinc is enriched in the alloy. A carbon- and oxygen-rich band within the film suggests that the films grow at the metal/film and film/electrolyte interfaces.