Mechanical alloying during cryomilling of a 5000 Al alloy/AlN powder:: the effect of contamination

Elemental powders of 80 vol% 5000 Al alloy (3 wt% Mg) and 20 vol% AlN were milled either in liquid nitrogen or at room temperature under argon. The milling of the mixture involved changes in the chemical composition: Fe contamination, oxidation and in-situ nitridation. The effects of milling time and temperature on the contamination of the system were analysed. Oxidation and in-situ nitridation were characterized by a LECO analyser and thermal desorption measurements, whereas Mossbauer spectroscopy was used to study the mechanical alloying of the Al alloy. The results show that a metastable solid solution of Mg and Fe in Al is formed during cryomilling. The occurrence of mechanical alloying in spite of the very low milling temperature is interpreted as a consequence of the fine crystallite size of the Al matrix. (C) 2001 Elsevier Science B.V. All rights reserved.