FORMATION AND HIGH MECHANICAL STRENGTH OF AL-BASED ALLOYS CONTAINING A NANOSCALE ICOSAHEDRAL PHASE AS A MAIN CONSTITUENT

This paper reviews our recent results on the achievement of high tensile strength and good ductility for rapidly solidified Al-Mn-Ln and Al-Cr-Ln (Ln=lanthanide metal) alloys containing an icosahedral phase as a main constituent phase. The good mechanical properties are attributed to the simultaneous achievement of the following three structural effects resulting from rapid solidification and appropriate alloy design; (1) the formation of a mixed structure consisting of nanoscale icosahedral particles surrounded by Al phase, (2) the formation of the icosahedral phase at low solute concentrations, (3) the achievement of an ultra-fine mixed state of icosahedral and approximant regions caused by the phason strain-induced approximant transition in the nanoscale icosahedral particles. The utilization of the structural effects is expected to cause high mechanical strengths combined with good ductility for other quasicrystalline alloys.