The structural-phase states and defect substructure of silumin subjected to high-intensity electron beam irradiation in different modes and subsequent fatigue loading up to failure are analyzed via scanning and transmission electron diffraction microscopy. It is found that the sources of fatigue microcracks are micronand submicron-sized silicon plates that remain undissolved during electron-beam treatment. Possible reasons for the longer fatigue life of silumin after electron-beam treatment are discussed.