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Al-0.61wt%Fe and Al-1.9wt%Fe alloys were atomized in helium and nitrogen atmospheres, using impulse atomization. The microstructure of the droplets atomized in helium and nitrogen were characterized using a number of techniques including X-ray diffraction, micro-tomography and scanning electron microscopy (SEM). In both alloys, a fully dendritic microstructure with -Al present as the primary phase and lamellar interdendritic regions were found. The volume fraction of eutectic was measured as a function of particle size, atomized gas and Fe content. These measurements clearly indicate that a significant amount of microsegregation and metastability occurs for both alloys. Measurements of the volume fraction of eutectic were used to estimate the degree of eutectic undercooling. It is found that assuming that the eutectic is composed of -Al and Al 4 Fe phases, the undercooling is about 10°C and 17°C for the 0.61 and the 1.9 wt% Fe alloys. The maximum solubility of Fe in the primary -Al phase is 0.068 wt% and 0.12 wt% in the 0.61 and 1.9 wt% Fe alloys and the eutectic is found at 3.1 and 5.5 wt% Fe for these two alloys, respectively. Calculated cooling rates using the metastable values of the phase diagram for each alloy showed that the cooling rates ranged from 20 to 10,000 K/s. The measured cell spacing , was linked to the cooling rate CR according to the equation  = B ¥ CR -n where B and n are constants, depending on the composition of the alloy. Good agreement was found between the experimentally determined coefficients B and n and those calculated from the coarsening model proposed by Kurz and Fisher [1].

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