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The oxidation of Cu-6.8Al (at.%) alloy has been studied at 800 and 900 degrees C in 1 x 10(5) Pa pure O-2. The scales formed at 800 degrees C are composed of a thin outer CuO layer and an inner protective Al2O3 layer. On the contrary, at 900 degrees C different samples of the alloy present two kinds of different oxidation behavior: one is protective, very similar to that at 800 degrees C. while the other is intermediate between protective and non-protective, with formation of very thick scale on the partial surface, which is mainly composed of copper oxides. The different behavior presented on a single sample is probably caused by local inhomogeneities of the alloy. It is deduced that at 900 degrees C the critical Al content to form external-alumina scale on Cu-Al alloy is about 6.8 at.%. (C) 2006 Elsevier Ltd. All rights reserved.