Jh. Nordlien et al., MORPHOLOGY AND STRUCTURE OF WATER-FORMED OXIDES ON TERNARY MGAL ALLOYS, Journal of the Electrochemical Society, 144(2), 1997, pp. 461-466
Oxides on ternary magnesium alloys MgAlZn and MgAlRE were investigated
by transmission electron microscopy using ultramicrotomed film sectio
ns. These films have a three-layered structure, similar to pure Mg and
binary MgAl alloys, characterized by a hydrated inner layer, a thin a
nd dense intermediate region, and a platelet-like-outer layer. Zinc an
d rare-earth elements present in the two types of ternary alloys becom
e incorporated in the oxide film so as to increase its stability in an
aqueous environment, in particular by reducing hydration and increasi
ng resistance to magnesium egress of the inner layer, which is respons
ible for the passivity of the surface. The apparent presence of trace
amounts of rare-earth oxides in the film is particularly effective in
improving passivity of the surface and, thereby, the corrosion resista
nce of MgAlRE alloys. The presence of aluminum together with rare-eart
h elements (RE) in the alloy is an essential factor in obtaining these
results.