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An Al94Mn2Be2Cu2 cast alloy was developed displaying increased quasicrystalline formation ability at moderate cooling rates. The as-cast microstructure consisted of a mainly icosahedral phase in the Al-matrix. The microstructure remained stable during uniform heating to 580 °C and isothermal annealing at 400 °C. Most of the icosahedral phase was preserved even after 24 h annealing at 500 °C. For that reason, this alloy presents a promising basis for further development of cast Al-alloys containing quasicrystals.

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SummaryAn Al 86 Mn 3 Be 11 alloy cast into copper mould was subjected to metallographic investigation. The as-cast microstructure consisted of a quasicrystalline icosahedral phase (i-phase), Be 4 AlMn phase and, occasionally, a hexagonal phase. Alrich solid solution represented the dominant phase. The chemical compositions of phases were determined using AES. The composition of the Be 4 AlMn slightly deviated from the stoichiometric composition, whereas the composition of the i-phase was approximately Al 52 Mn 18 Be 30 , containing an appreciable amount of Be. The average composition of the hexagonal phase was Al 66 Mn 21 Be 13 . Deep etching and particle extraction provided a deep insight into the threedimensional morphology of the i-phase and the hexagonal phase, whereas Be 4 AlMn was slightly attacked by the etchant. The i-phase was present predominantly in the form of dendrites and a rodlike eutectic phase. The hexagonal phase was primarily in the form of hexagonal platelets, whereas Be 4 AlMn was rather irregular in shape. The morphology of the i-phase can be explained by predominant growth in 3-fold directions and the lowest energy of the 5-fold planes, leading to the faceting and adopting a pentagonal dodecahedron shape. The brightnesses of phases in the backscattered electron images were rationalized by determining their backscattering coefficients. TEM investigation showed considerable phason strain in the i-phase, and the polycrystalline nature of the Be 4 AlMn phase.

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