Synthesis of octahedron and truncated octahedron primary Mg2Si by controlling the Sb contents

Abstract

Octahedron and truncated octahedron primary Mg₂Si were prepared by increasing the contents of Sb in an Al–Mg–Si melt. The structure and morphologies of primary Mg₂Si were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The modifier Sb plays an important role in determining their morphologies, which can transform from equiaxed-dendrite to octahedron and finally to truncated octahedron (tetrakaidecahedron) with an increase in Sb content. An adsorption model demonstrates that Sb atoms preferentially adsorb on {100} facets of the Mg₂Si crystal, which is the key reason for the morphology evolution. Moreover, the growth processes of octahedron and truncated octahedron primary Mg₂Si modified by Sb element have been revealed for the first time. Our study suggests that it is feasible to control the morphologies of primary Mg₂Si crystals in metallic melts by a simple method modification, which is critical to the development of advanced structural alloys with high strength and toughness.