Abstract: Proper addition of 0.002 wt-% Mg to cast Fe_3Al alloy may obviously improve the room and high temperature tensile properties.Auger spectra show that Mg segregates near grain boundaries as very thin layers.Observation under TEM reveals that a suitable amount of Mg enhances ability of cooperative internal deformation so that the dislocations will ease the con- tinuous slip deformation through grain boundaries.The fracture feature of Fe_3Al alloy is of transgranular cleavage at room temperature and cracks initiate at grain boundaries.

Key words: Fe_3Al, intermetallic compound, microalloying, mechanical property