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 alloys with a surface texture characterized by branched and dendritic disordered features of low Mg concentration having a lateral 2-D fractal dimension DB ≈ 1.77. Phase separation of areas with high (~ 38% at.) and low (~ 14% at.) Mg content allows direct observation of distinct differences in Mg surface segregation and oxidation across disordered phase boundaries. Nanometer scale lateral observation of these phenomena is feasible due to the nanometer spot size (~ 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 strongly correlated laterally with the Mg content.