PHASE SELECTION IN UNDERCOOLED QUASI-CRYSTAL-FORMING AL-MN ALLOY MELTS

Small droplets in size of 20-1000-mu-m of Al-Mn alloys have been undercooled by containerless solidification during free fall in a drop tube or by melt atomization. The as-solidified droplets were analyzed with respect to the phases formed from the undercooled melt by electron microscopy, x-ray diffraction, and differential thermal analysis. Depending on the droplet size, various phases have been identified ranging from supersaturated Al(SS), intermetallic Al6Mn, to quasicrystalline phases. The observed phase formation was interpreted in terms of nucleation, crystal growth, and transformation kinetics on the basis of current theories. This analysis gives a comprehensive description of phase formation in undercooled Al-Mn alloys in agreement with the experimental findings.