Al-3Fe alloys with nearly full Al6Fe fibers are obtained via iron mold casting at different mold temperatures (293 K, 323 K, 373 K, and 423 K). The shapes of the Al6Fe fibers and their spatial distribution in the alloys are characterized by scanning electron microscopy and transmission electron microscopy. Thermal curves are recorded to help analyze the solidification behavior. The influence of thermal field on the solidification behavior of Al-Al6Fe eutectic is analyzed by comparing the detailed portraits of Al6Fe fibers via the deep etching method. The microstructures in the central area of the ingots are more complex and variable with the change of mold temperature. The morphologies of Al6Fe fibers under different conditions are presented and exhibit strong regional characteristics. The solidified manner of Al6Fe phases in the central region is believed to be affected by a local negative temperature gradient caused by the homogenous nucleation of equiaxed eutectic colonies. The selection of types of secondary phases in the undercooling melt in central areas is found to be closely related to the latent heat releasing rate.