Phase-Field Simulation of Microsegregation and Dendritic Growth During Solidification of Hypoeutectic Al-Cu alloys

Alexandre Furtado Ferreira,Zilmar Alcântara Júnior,Paulo Felipe Junior,Amauri Garcia,Késsia Gomes Paradela

doi:10.1590/1980-5373-mr-2016-0194

Abstract

Prediction of microstructure evolution and microsegregation is one of the most important problems in materials science. The dendritic growth and microsegregation provide a challenging simulation goal for computational models of solidification, in addition to being an important technological feature of many casting processes. The phase-field model offers the prospect of being able to perform realistic simulation experiments on dendrite growth in metallic systems. In this paper, the microsegregation and dendritic growth of hypoeutectic Al-Cu alloys under constant cooling rate was simulated using a phase-field model. The main new feature of the present model is based on the fact that the effect of the growth rate is incorporated via an effective partition coefficient that has been experimentally determined for a range of growth rates. It is shown that both models (Phase-field model and Scheil) have significant deviations from the experimental data when the equilibrium partition coefficient is considered in the calculations. Since the predicted results using the models yielded discrepancies from the experimental data, an experimental equation is adopted for calculating the effective partition coefficient from experimental data. The experimental equation is then adopted in the calculations of phase-field model and Scheil's equation, showing a good agreement with the experimental data.

Highlights

Solidification processing is one of the important routes to produce metallic materials, especially alloys
The system temperature is uniform and continuously decreased with a constant cooling rate from the initial temperature (T0), which is slightly lower than the liquidus temperature of the Al–Cu alloy
Where T0 is the initial temperature, Ṫ represents a constant value for the cooling rate and t is the solidification time

Summary

Introduction

Solidification processing is one of the important routes to produce metallic materials, especially alloys. In contrast to the previous phase-field models, in the present paper the numerical results are achieved in the simulations by disregarding the equilibrium partition coefficient (Ke) and, instead, imposing an effective partition coefficient (Kef). The aluminium alloys (Al-CU) have been chosen taking into account their high strength, which is achieved by the heat treatment process, the cast aluminium alloys yield cost-effective products due to the low melting point In this present paper, the phase-field model is applied in solidification of two binary alloys Al-2.64×10−2mol%Cu (6.0wt.%Cu) and Al-4.5×10−2mol%Cu (8.9wt.%Cu). Experimental microsegregation profiles from the central part of the dendrite cores to the limit of the interdendritic regions were determined by Meza et al.[15] in the different growth rates In this present paper, it is assumed that said alloys are diluted; the copper is completely soluble in the aluminium. The microsegregation profiles predicted by both the phase-field model and Scheil’s equation, using the new partition coefficient, are compared with experimental data

Governing Equations

Results and discussion

Conclusions