CHARACTERIZATION OF AS-SPUN AND ANNEALED Al-Mn-Fe RIBBONS

Microstructure of conventionally cast and melt spun Al91Mn7Fe2 alloy was examined by X-ray diffraction, SEM and TEM techniques. Three different phases were found in a mould cast ingot: Al-6(Mn, Fe), Al-4(Mn, Fe) and aluminium solid solution. Rapidly quenched ribbons cast using melt spinning technique with different speed values of rotating wheel: 25, 30 and 36 m/s had average width in a range of 30-50 mu m. It was found that ribbons contain quasicrystalline particles with different sizes and shapes including large dendrites in a range of micrometers and smaller spherical particles below 1 mu m embedded in an aluminium matrix. Composition of these particles was similar to the Al-4(Mn, Fe) phase. Also quasicrystals in the form of eutectic were observed with slightly different composition close to the Al-6(Mn, Fe) phase. All observed particles revealed 2, 3 and 5- fold symmetry, typical for icosahedral quasicrystals. Increase in microhardness up to 274 HV for melt spun ribbon comparing to 141 HV for the as-cast ingot was observed due to a change in phase composition and refinement of the phases. Thermal stability of quasicrystalline phase in the ribbon was examined by annealing in different temperatures. Temperatures for thermal treatment were chosen based on DSC curve which contains the exothermic peak in the temperature range 300-500 degrees C. Analysis of ribbons annealed for 30 minutes at 400 degrees C showed that transformation of quasicrystals to stable crystalline phase starts at quasicrystal/Al-matrix interfaces. After annealing for 4 hours at 500 degrees C only the Al-6(Mn, Fe) phase and aluminium solid solution were observed in the ribbon microstructure.