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

Highlights: • Barrier anodic films formed on ZE41 Mg alloy in glycerol/fluoride electrolyte. • Films contain oxygen and fluorine species; formation ratio ∼1.3 nm V⁻¹. • Nanocrystalline film structure, with MgO and MgF_2. • Zinc enrichment in alloy beneath anodic film. • Modified film formed above Mg-Zn-RE second phase. - Abstract: 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