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

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.