Work

Modification mechanism of Te and morphology evolution of primary Mg2Si in an Al-20Mg2Si alloy

Year: 2024

Type: article

Abstract: In the present work, the modification effect of Te and the corresponding growth process of Mg2Si were clarified. With 0.5 wt.% Te addition, the dendritic primary Mg2Si transformed to polygons, accompanied by a reduction in size from over ~150 μm to ~20 μm. However, 2.0 wt.% Te addition resulted in degradation of modification effect, and the morphology of Mg2Si changed to dendrite. Three-dimensional morphology of primary Mg2Si indicated that the modifier Te altered the morphology of primary Mg2Si from dendrites to polyhedrons surrounded by {111} and {100} planes. The modification mechanism of Te can be attributed to the heterogeneous nucleation and the doping of Te during the growth process of primary Mg2Si, which greatly contributed to dimension decrease and the final morphology of primary Mg2Si respectively. With Te corporation, the relative surface energy between the {100} and {111} (r) drops, contributing to the exposure of {100} planes. Interestingly, our work shows that the solute concentration under non-equilibrium solidification plays an important role in determining the final morphology of Mg2Si. The preferential segregation of local Mg and Si solutes results in the degradation of dendrite arms in other directions during the initial phase of crystal growth. Combined with the modifying effect of Te, which alters the surface energy of the crystal, the resulting crystal morphology deviates from its equilibrium state, such as dodecahedron, flat truncated octahedron and so on. Our study demonstrates that ultimate morphology and dimensions of primary Mg2Si can be determined simultaneously with the addition of certain modifiers, which can be achieved by regulating the growth and nucleation of Mg2Si at the same time.

Source: Heliyon

DOI: 10.1016/j.heliyon.2024.e40141