Abstract
A coupled cellular automaton-finite difference (CA-FD) model is used to simulate the detailed dendritic structure evolution of the columnar-to-equiaxed transition (CET) for Al-Cu alloys during solidification. The effects of material properties (nucleation undercooling, density of nuclei in bulk liquid and alloy solidification range) on the CET are investigated. Simulated results reveal that: (1) equiaxed grains form at an earlier stage with a smaller critical nucleation undercooling; (2) CET is promoted if the density of nuclei in bulk liquid is increased; (3) extending the alloy solidification range promotes the CET. Finally, CET maps corresponding to different alloy concentrations are constructed, illustrating the relationship between processing conditions and the resulting grain structures for alloys with different solidification ranges.
Highlights
In castings, there are two distinct grain structures, columnar and equiaxed, which are mainly determined by material properties and solidification conditions
In direct-chill and die castings, columnar grains form near the mould surface and grow perpendicular to the isotherms, and transform to equiaxed grains in the lower thermal gradient area near the centre of the casting
Temperature gradient (G) of 3.0 K/mm was imposed to move from the bottom to the top with a pulling velocity (V) using the relation: V=100+20×t to simulate the thermal profile of directional solidification in experiments
Summary
There are two distinct grain structures, columnar and equiaxed, which are mainly determined by material properties and solidification conditions. A coupled cellular automaton-finite difference (CA-FD) microstructural model is used to simulate the detailed dendritic structure evolution and to investigate the effect of material properties (critical nucleation undercooling, density of nuclei in bulk liquid and alloy solidification range) on the CET.
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