SOLIDIFICATION OF AL-CU-FE ALLOYS FORMING ICOSAHEDRAL PHASE

The solidification of a series of Al-Cu-Fe alloys containing an icosah edral phase has been studied by scanning electron microscopy, energy-d ispersive x-ray spectroscopy, powder x-ray diffraction, and differenti al thermal analysis. The constitution and morphology of alloys solidif ied at different rates are presented, The overall compositional range of the icosahedral phase was determined in as-cast, slowly solidified alloys and those annealed at 800 and 600 degrees C. The solidification of this phase follows closely the Al3Fe-AlCu compositional direction. The first icosahedral phase solidified close to Al65.5Cu21.5Fe13; its compositional region at 800 degrees C Lies between about Al64.5Cu23Fe 12.5 and Al62Cu26.5Fe11.5, while at 600 degrees C it lies between Al62 Cu26.5Fe11.5 and Al60.5Cu29.5Fe10. The formation of the icosahedral an d related structures observed in Al-Cu-Fe alloys is discussed.