CAFE simulation of columnar-to-equiaxed transition in Al-7wt%Si alloys directionally solidified under microgravity

D R Liu,Ch-A Gandin,H Nguyen Thi,G Zimmermann,L Sturz,B Billia,N Mangelinck-Noël

doi:10.1088/1757-899x/117/1/012009

Abstract

A two-dimensional multi-scale cellular automaton - finite element (CAFE) model is used to simulate grain structure evolution and microsegregation formation during solidification of refined Al-7wt%Si alloys under microgravity. The CAFE simulations are first qualitatively compared with the benchmark experimental data under microgravity. Qualitative agreement is obtained for the position of columnar to equiaxed transition (CET) and the CET transition mode (sharp or progressive). Further comparisons of the distributions of grain elongation factor and equivalent diameter are conducted and reveal a fair quantitative agreement.

Highlights

Grain morphology has a great influence on the final performance of as-cast products [1]
The cellular automaton - finite element (CAFE) simulations are first qualitatively compared with the benchmark experimental data under microgravity
Qualitative agreement is obtained for the position of columnar to equiaxed transition (CET) and the CET transition mode

Summary

Introduction

Grain morphology has a great influence on the final performance of as-cast products [1]. Direct macroscopic modelling, such as cellular automaton - finite element (CAFE) model, has been developed by Gandin and co-workers with advantages in numerically investigating CET [7,8]: at the size of casting, the topological description of grain structure transition and composition heterogeneity can be realized. The definition of CET position between transition zone and equiaxed region is dependent on the distribution pattern of averaged elongation factor along the solidification direction. The difference in CET transition manner between FM1 and FM5 is explained as: a pulling-velocity jump used in FM1 leads to a higher degree of constitutional undercooling ahead of the solidification front Under such condition, the nucleation rate is enhanced. With an intensive and frequent nucleation of grains in the liquid, the newly nucleated grains compete over the continued growth of existing grains to form a truly equiaxed zone after columnar zone [9]

Modelling

Results and discussion

CET min

Conclusion