Characterization of oxide films formed on Mg-based WE43 alloy using AC/DC anodization in silicate solutions

The characteristics of the oxide film formed on a Mg-based WE43 alloy using ac/dc anodization techniques in an alkaline silicate solution have been investigated using scanning electron microscopy and Rutherford back-scattering spectroscopy, and the corrosion resistance of these films has been determined using the ac impedance technique. The oxide film was found to be composed of MgO, Mg(OH)(2), MgF2, and SiO2, and consisted of an inner barrier and an outer porous oxide film, both of which increased linearly in thickness with the applied anodization voltage. High applied voltages and current densities also led to the formation of large pores, having diameters greater than 6 mum, and the partial sealing of small pores in the outer layer. Allowing the current to decay for a period of time in the later stages of anodization led to an increase in the thickness of both the barrier and porous films and further sealing of the film pores. A correlation of the oxide corrosion resistance with the barrier film thickness is also demonstrated. (C) 2003 The Electrochemical Society.