Formation and stability of quasicrystalline and hexagonal approximant phases in an Al-Mn-Be alloy

Phase formation and thermal stability for an Al-Mn-Be alloy have been investigated by melt-spinning and conventional casting. Significant differences in the phase formation and the thermal stability of the microstructure were found as a result of the different cooling rates. In the melt-spun ribbons, a large volume fraction of a metastable icosahedral phase was found to coexist with an Al solid solution. In the bulk cast ingots, the primary phase formed in the two-phase microstructure was a hexagonal approximant phase of quasicrystals. This phase that solidified in the form of faceted particles embedded in the Al solid matrix proved to be thermodynamically stable during annealing at 540 degreesC for 100 h. The effect of Be addition on the formation of the stable approximant phase is discussed in terms of the Hume-Rothery mechanism.