Numerical modelling of acoustic streaming during the ultrasonic melt treatment of direct-chill (DC) casting

Lebon, Bruno; Salloum-Abou-Jaoude, G.; Eskin, Dmitry; Tzanakis, Iakovos; Pericleous, K.; Jarry, Philippe

doi:10.1016/j.ultsonch.2019.02.002

Cited by 90 publications

(94 citation statements)

References 36 publications

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“…Lowering the sonotrode may invoke fragmentation of dendrites from the slurry zone of the billet with their recirculation and redistribution by acoustic streaming as has been reported elsewhere. [22] The position of the sonotrode with respect to the liquidus isotherm explains the strong grain refinement effect achieved in the permanent mold. In this case, the liquidus is constantly moving towards the sonotrode and the acoustic streaming efficiently interacts with the slurry zone, extracting the dendrites from there and transporting them upwards towards the sonotrode and the cavitation zone.…”

Section: A Microstructure Refinement and Modificationmentioning

confidence: 99%

“…This phenomenon was previously discussed elsewhere. [22] In the permanent mold, on the other hand, there is no continuous feeding of hot melt into the billet, and therefore the liquid temperature keeps decreasing as solidification progresses, resulting in flattening of the liquidus position in the sump and a flatter sump profile. Since the dominant mechanism for Al grain refinement in our experiments is dendrite fragmentation, the narrowing of the mushy zone in DC casting (due to the depression of the liquidus isotherm) reduces the effectiveness of this fragmentation mechanism, additionally contributing to a lesser grain refinement observed (see Figure 6).…”

Section: A Microstructure Refinement and Modificationmentioning

confidence: 99%

“…Similar grain growth effects supported by computer simulations of acoustic streaming have been reported recently elsewhere. [22] As the USP casting reached steady-state condition (USP zone), a relatively stable flow balance is re-established between the natural convection flow and the forced downward convection flow from sonotrode. This explains the relatively small negative centerline segregation and overall lesser macrosegregation across the billets' diameter for both casting cases studied (Figure 11(a)).…”

Section: A Microstructure Refinement and Modificationmentioning

confidence: 99%

See 2 more Smart Citations

Structure Modification upon Ultrasonic Processing of an AA4032 Piston Alloy: Comparison of Permanent Mold and Direct-Chill Casting

Chankitmunkong

Eskin

Limmaneevichitr

2019

Metall Mater Trans A

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Piston Al-Si alloys have very complex compositions and multi-phase heterogeneous structure, so it is necessary to control the formation of primary and eutectic compounds. In this study, the ultrasonic melt processing (USP) of a eutectic Al-Si piston alloy (AA4032-type) was performed in a permanent mold and during direct-chill (DC) casting to study its effects on the structure refinement and modification. The principal difference between these two ways of casting is that in the permanent mold the solidification front progressively moves towards the ultrasound source, while in the DC casting the position of the solidification front is fixed in space. The results showed that the USP can successfully refine primary Si, Fe-containing intermetallics and aluminum grains. Refinement of primary Si was accompanied by the increase in its amount, which was attributed to both enhanced heterogeneous nucleation and fragmentation. The refinement of Fe-containing intermetallics and Al grains resulted from the fragmentation mechanism and were more pronounced when USP was applied below the liquidus temperature in the permanent mold. However, the eutectic phases coarsened upon USP, and this effect was most pronounced when USP was applied to the semi-solid material. This was related to the strong attenuation of acoustic waves, which effectively heats the semi-solid material and induces corresponding coarsening of the phases. Acoustic streaming induced by an oscillating sonotrode affected the depth of the sump while simultaneously decreasing the macrosegregation, which reflects the dominant role of the melt flow directed against natural convection. The results demonstrated the importance of the solidification stage at which the USP was applied and the specifics of the USP mechanisms acting at the different stages of solidification.

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Section: A Microstructure Refinement and Modificationmentioning

confidence: 99%

Section: A Microstructure Refinement and Modificationmentioning

confidence: 99%

Section: A Microstructure Refinement and Modificationmentioning

confidence: 99%

See 1 more Smart Citation

Structure Modification upon Ultrasonic Processing of an AA4032 Piston Alloy: Comparison of Permanent Mold and Direct-Chill Casting

Chankitmunkong

Eskin

Limmaneevichitr

2019

Metall Mater Trans A

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“…Computer simulations were performed using our own modelling approach implemented in OpenFOAM 6. The details can be found elsewhere [7].…”

Section: Methodsmentioning

confidence: 99%

Altering the Microstructure Morphology by Ultrasound Melt Processing During 6XXX Aluminium DC-Casting

et al. 2019

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In this work, we have introduced power ultrasound in the sump during hot-top DC casting of 152 mm Ø billets to influence the aluminium grain growth morphology. Grains in the central part of the billet are highly dendritic and elongated towards the sonotrode position in the sump. We suggest that ultrasound generates acoustic flow in the sump counteracting natural convection, thereby affecting the direction of grain growth; this is supported by numerical modelling. We found that macrosegregation can be decreased by tuning the position of the sonotrode in the sump and the ultrasonic power. Apart from the central part of the billet, the grain size was found to be significantly refined compared with the reference cast. This could be an effect of forced dendritic fragmentation by ultrasonic melt processing.

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“…These in-situ solidification studies have increased our current understanding by elucidating the role of cavitation bubbles and explained the importance of these mechanisms for the upscaling of UST to large melt volumes in industrial applications. Considerable research has also highlighted the importance of cavitation and acoustic streaming on the activation of potent particles, nucleation of grains, altering convection patterns and reducing the temperature gradients during solidification [23,[26][27][28][36][37][38][39][40]. While recent publications on advanced (in-situ) solidification studies have provided more detailed evidence on bubble dynamics during melt solidification [31][32][33]41,42], our research has been focused on other factors such as solute content, type of solute, constitutional supercooling, role of potent and impotent (oxide) particles, UST duration, origin and transport of grains, temperature range over which UST is applied, sonotrode preheating and other casting variables that could affect grain formation [6,37,38,[43][44][45][46][47].…”

Section: Introductionmentioning

confidence: 99%

Ultrasonic Cavitation Treatment of Metallic Alloys

Eskin¹,

Tzanakis²

2020

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The current trend in solidification research is to develop a generic, energy-efficient, economical, sustainable, and pollution-free technology that can be applied to different alloy systems. Ultrasonic-cavitation melt treatment (UST) is a rather universal technology that can be applied to conventional and advanced metallic materials, regardless of their composition, while being environmentally friendly, cost effective, and ready to be implemented in conventional casting technologies such as direct-chill, continuous, or shape casting, as well as in emerging technologies of additive manufacturing and nanocomposite materials. The beneficial effects of UST-such as in assisted nucleation, activation of substrates (wetting), deagglomeration and fragmentation of solid phases, degassing of the melt, and grain refinement of the as-cast product-stem from the growth, collapse, and implosion of cavitation bubbles as aresult of alternate fluctuations in ultrasonic pressure. Although successfully demonstrated on the laboratory and pilot scale, UST has not yet found widespread industrial implementation. This is mostly due to the lack of in-depth understanding of the fundamental mechanisms behind the improved metal quality and structure refinement. Thus, fundamental research is needed to answer the following practical questions: What is the optimum melt flow rate that maximizes treatment efficiency whilst minimizing input power, cost, and plant complexity? What is the optimum operating frequency and acoustic power that accelerates the treatment effects? What is the optimum location of an ultrasonic power source in the melt transfer system in relation to the melt pool geometry? Answering these questions will pave the way for widespread industrial use of ultrasonic melt processing with the benefit of improving the properties of lightweight structural alloys, simultaneously alleviating the present use of polluting (Cl, F) for degassing or expensive (Zr, Ti, B, Ar) grain refinement additives.

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Numerical modelling of acoustic streaming during the ultrasonic melt treatment of direct-chill (DC) casting

Cited by 90 publications

References 36 publications

Structure Modification upon Ultrasonic Processing of an AA4032 Piston Alloy: Comparison of Permanent Mold and Direct-Chill Casting

Structure Modification upon Ultrasonic Processing of an AA4032 Piston Alloy: Comparison of Permanent Mold and Direct-Chill Casting

Altering the Microstructure Morphology by Ultrasound Melt Processing During 6XXX Aluminium DC-Casting

Ultrasonic Cavitation Treatment of Metallic Alloys

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