Enrichment of alloying elements in anodized magnesium alloys

Abstract The possibility of enrichment of alloying elements in magnesium alloys as a consequence of growth of an anodic film has been investigated for sputtering-deposited Mg–0.4 at.% W and Mg–1.0 at.% W alloys. The alloys were anodized at 10 mA cm −2 to various voltages, up to 150 V, in 3 M ammonium hydroxide/0.05 M ammonium phosphate electrolyte at 293 K. The alloys revealed enrichments of tungsten to at least 1.7×10 15 and 2.9×10 15 W atoms cm −2 for the Mg–0.4 at.% W and Mg–1.0 at.% W alloys respectively. The enrichment behaviour appears to be similar to that in dilute aluminium alloys, which occurs for alloying elements with oxides having Gibbs free energies per equivalent for formation exceeding that for formation of alumina.