The effect of free-floating dendrites and convection on macrosegregation in direct chill cast aluminum alloys

Vreeman, Christopher J.; Krane, Matthew John M.; Incropera, F. P.

doi:10.1016/s0017-9310(99)00174-x

Cited by 117 publications

(78 citation statements)

References 14 publications

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“…Researchers have also utilized the modelling approaches to investigate how the movement of solid grains influences macrosegregation [95,96] Due to gravity (in the case when the solid phase density is higher than that of the liquid phase) the floating grains tends to settle down while being swept by the surrounding liquid. The liquid also exerts a resistance for this sedimentation.…”

Section: Movement Of Equiaxed Grains ('Floating' Grains)mentioning

confidence: 99%

“…A simple expression which was derived from the Stokes law was used to approximate the solidliquid velocity differences [97]. It was concluded that the floating dendrites were responsible for the centreline negative macrosegregation [96]. Another approach could be the two-phase model with one phase for the grains and the other for the liquid, in which the interaction between these two phases is modelled by a drag force present in the momentum equations of each phase.…”

Section: Movement Of Equiaxed Grains ('Floating' Grains)mentioning

confidence: 99%

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Macrosegregation in direct-chill casting of aluminium alloys

Nadella

Eskin

et al. 2008

Progress in Materials Science

249

148

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Semi-continuous direct-chill (DC) casting holds a prominent position in commercial aluminium alloy processing, especially in production of large sized ingots.Macrosegregation, which is the non-uniform chemical composition over the length scale of a casting, is one of the major defects that occur during this process. The fact that macrosegregation is essentially unaffected by subsequent heat treatment (hence constitutes an irreversible defect) leaves us with little choice but to control it during the casting stage. Despite over a century of research in the phenomenon of macrosegregation in castings and good understanding of underlying mechanisms, the contributions of these mechanisms in the overall macrosegregation picture; and interplay between these mechanisms and the structure formation during solidification are still unclear. This review attempts to fill this gap based on the published data and own results. The following features make this review unique: results of computer simulations are used in order to separate the effects of different macrosegregation mechanisms. The issue of grain refining is specifically discussed in relation to macrosegregation. This report is structured as follows. Macrosegregation as a phenomenon is defined in the Introduction. In Part 2, direct-chill casting, the role of process parameters and the evolution of structural features in the as-cast billets are described. In Part 3, macrosegregation mechanisms are elucidated in a historical perspective and the correlation with DC casting process parameters and structural features are made. The issue of how to control macrosegregation in direct-chill casting is also dealt with in Part 3. In Part 4, the effect of grain refining on macrosegregation is introduced, the current understanding is described and the contentious issues are outlined. The review is finished with conclusion remarks and outline for the future research.

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Section: Movement Of Equiaxed Grains ('Floating' Grains)mentioning

confidence: 99%

Section: Movement Of Equiaxed Grains ('Floating' Grains)mentioning

confidence: 99%

Macrosegregation in direct-chill casting of aluminium alloys

Nadella

Eskin

et al. 2008

Progress in Materials Science

249

148

View full text Add to dashboard Cite

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“…When the growing solid particles interlock with each other, solidification shrinkage-induced liquid flow drives the solute-rich liquid to the periphery of the billet through the interdendritic channels, which generally leads to macroscopic level compositional nonuniformity over the horizontal section of the billet. 14,15) As the solidification processes of most aluminium and magnesium alloys are all characterized by the formation of dendrites, 16) such macrosegregation in the aluminium and magnesium alloys are mainly caused by the flow behaviors of the interdendritic liquid-phase. This explains large-scale nonuniformity for the solutes in the AZ80 billet that is cast in conventional process.…”

Section: Discussionmentioning

confidence: 99%

The Effects of Electromagnetic Vibration on Macrosegregation in AZ80 Magnesium Alloy Billets

Guo¹,

Le²,

Han³

et al. 2006

Mater. Trans.

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The effects of electromagnetic vibration on macrosegregation in AZ80 magnesium alloy billets have been investigated experimentally. Comparing to conventional direct-chill casting, the enrichment for the alloying elements close to the billet surface is significantly reduced by the electromagnetic vibration. Increasing the stationary magnetic field, i.e., increasing the intensity of the electromagnetic vibration results in uniform distributions of the metallic elements in the billet. The distribution of impurity iron has the same tendency with alloying element manganese with and without the electromagnetic vibration. The uniformity in the concentration profile of iron is higher than that for the alloying elements in the billet and increases with increasing the stationary magnetic field of the system used for generation of electromagnetic vibration.

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“…The momentum equations are from Vreeman et al [3], who included the effect of free-floating solid grains. This solid forms on grain refiners initially and has increasing interactions among themselves as they solidify.…”

Section: Description Of Deterministic 2d Solidification Modelmentioning

confidence: 99%

Uncertainty Quantification of Modelling of Equiaxed Solidification

Fezi¹,

Krane²

2016

IOP Conf. Ser.: Mater. Sci. Eng.

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Abstract. Numerical simulations of metal alloy solidification are used to gain insight into physical phenomena that cannot be observed experimentally. Often validation of such models has been done through comparison to sparse experimental data, to which agreement can be misinterpreted due to both model and experimental uncertainty. Uncertainty quantification (UQ) and sensitivity analysis are performed on a transient model of solidification of Al-4.5 wt.% Cu in a rectangular cavity, with equiaxed (grain refined) solidification morphology. This model solves equations for momentum, temperature, and species conservation; UQ and sensitivity analysis are performed for the degree of macrosegregation. A Smolyak sparse grid algorithm is used to select input values to construct a response surface fit to model outputs. The response surface is then used as a surrogate for the solidification model to determine the sensitivities and probability density functions of the model outputs. Uncertain model inputs of interest include the secondary dendrite arm spacing, equiaxed particle size, and fraction solid at which the rigid mushy zone forms. Similar analysis was also performed on a transient model of direct chill casting of the same alloy.

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The effect of free-floating dendrites and convection on macrosegregation in direct chill cast aluminum alloys

Cited by 117 publications

References 14 publications

Macrosegregation in direct-chill casting of aluminium alloys

Macrosegregation in direct-chill casting of aluminium alloys

The Effects of Electromagnetic Vibration on Macrosegregation in AZ80 Magnesium Alloy Billets

Uncertainty Quantification of Modelling of Equiaxed Solidification

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