Computer Simulations of the Aluminium-Silicon Anomalous Eutectic Growth Based on Multiphase Field Method

Abstract

Aluminium-silicon anomalous eutectic growth has been studied numerically using a phase-field model developed to predict multiple phases. The Si phase grew very slowly in a melt of eutectic composition, but then grew substantially faster when in contact with the solidifying Al phase. The Al-liquid interface was irregular while the Si-liquid interface was flat as a consequence of the low interfacial energy between liquid and Al phases compared with that between liquid and Si. By developing a mathematical nucleation criterion, eutectic growth patterns were predicted and are in good agreement with experimental observations. Two mechanisms were shown to stop locally the growth of the Si phase during solidification. The first is competitive growth between the Al and Si phases, and arises when faster growing Al surrounds the tip of the solidifying Si. The second is due to nucleation and growth of Al ahead of the solidifying Si. It also has been shown that the melt is more likely to be trapped within the Si phase than in the Al phase.

Continuous Twin Screw Rheo-Extrusion of an AZ91D Magnesium Alloy

“…[5] This conventional dendrite fragmentation theory provides a good explanation for solid particle multiplication but cannot explain why the detached fragments would grow into globules rather than dendrites. Recent experimental studies, [19,30] supported by computer simulations, [31,32] suggest that the turbulence of high shear helps transport the accumulated solute atoms away from the solid-liquid interface and stabilizes planar growth, restraining dendrite development. Hence, the nondendritic structure is believed to be essentially a direct result of spherical growth under the forced convection.…”

A phase-field model for the solidification of multicomponent and multiphase alloys

“…However, it is not suitable for a quaternary system. In the present simulations, one assumes that the phasefield mobility for each liquid-solid phase transitions equals 0.2 m 3 /J, which is about the same for the growth of fcc-Al and Si solid from aluminium-silicon eutectic alloys [25].…”

“…As the time evolves, the concentration of Si in front of the fcc-Al phase becomes progressively richer and richer, leaving a high constitutional undercooling of the Si phase. A new embryo is introduced when the solute concentration of Si is larger than 40% [25]. The new Si nuclei grow quickly along the Sirich liquid in front of the fcc-Al phase and consequently form the Si phase, which adopts a flake morphology.…”

Structure and dynamics of liquid Al1−xSix alloys by ab initio molecular dynamics simulations

“…The formation and properties of Al-Si alloys have been studied extensively by experiments [3][4][5][6][7][8][9][10]. It has been shown that the structure and properties of liquid alloys are dependent on the composition and temperature.…”