Magnesium surface segregation and oxidation in Al-Mg alloys studied with local probe scanning Auger-scanning electron microscopy

Magnesium surface segregation and oxidation were investigated in Al-Mg allo ys with a surface texture characterized by branched and dendritic disordere d features of low Mg concentration having a lateral 2-D fractal dimension D -B approximate to 1.77. Phase separation of areas with high (similar to 38% at.) and low (similar to 14% at.) Mg content allows direct observation of distinct differences in Mg surface segregation and oxidation across disorde red phase boundaries. Nanometer scale lateral observation of these phenomen a is feasible due to the nanometer spot size ( similar to 15-20 nm) of the electron beam. Preferential surface oxidation, which is manifest even up to temperatures close to the melting point of Al and Mg, is shown to be stron gly correlated laterally with the Mg content. (C) 1999 Elsevier Science B.V . All rights reserved.