Surface Characterisation of Water-Atomised Al–Zn–Mg–Cu Alloy Powders by SIMS and AES

 The present paper focuses on the characterisation of surface composition and alloying element in-depth distribution of water-atomised Al–Zn–Mg–Cu alloy powders by secondary ion mass-spectrometry and Auger electron spectroscopy. A pronounced segregation of Mg and some impurities (Fe, Ca, S) concurrently with some Zn depletion are observed on the powder surface. The oxide film formed on the powder surface mainly consists of Al and Mg oxides. The film is non-uniform in thickness: rather coarse surface oxide islands coexist with surface areas covered by a thin (<1.8 nm) oxide layer. The extent of surface oxidation is strongly affected by solidification conditions: The average thickness of the surface oxides increases with increasing particle size or with decreasing cooling rate. All alloying elements are homogeneously distributed in the bulk of individual particles. No significant differences in chemical composition between different particles of a given powder are observed. Received November 26, 1999. Revision September 25, 2001.