Phase composition and structure of hypereutectic silumin AK20 irradiated by a pulsed electron beam of sub-millisecond exposure duration

Abstract

In this study, the authors analyzed the structural-phase transformations in the surface layer of hypereutectic silumin AK20 (Al—20 wt. % Si), initiated by a sub-millisecond exposure to a pulsed electron beam. It has been established that irradiation of hypereutectic silumin with a pulsed electron beam (17 keV, (15–70) J/cm², 150 μs, 3 pulses, 0.3 s^-1) is accompanied by high-speed melting of a surface layer up to 120 μm thick, followed by high-speed crystallization with the formation of a cellular-columnar type structure with a transverse cell size of 0.5 to 2.9 μm. It has been shown that crystallization cells are formed by a solid solution based on aluminum and are separated by layers 120 to 700 nm thick, formed by amorphous and crystalline (nanocrystalline) silicon. It has been established that the sizes of cells and the layers separating them increase with increasing energy density of the electron beam. Using X‑ray diffraction analysis methods, changes in the parameters and micro-distortions of the crystal lattice of aluminum and silicon were revealed after exposure to a pulsed electron beam.