scholarly journals Multiphysics Modelling of Ultrasonic Melt Treatment in the Hot-Top and Launder during Direct-Chill Casting: Path to Indirect Microstructure Simulation

Metals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 674
Author(s):  
Christopher Beckwith ◽  
Georgi Djambazov ◽  
Koulis Pericleous ◽  
Tungky Subroto ◽  
Dmitry G. Eskin ◽  
...  
Keyword(s):  
Residence Time ◽  
Acoustic Streaming ◽  
Direct Chill ◽  
Hot Top ◽  
Microstructure Refinement ◽  
Microstructure Simulation ◽  
Melt Pool ◽  
Multiphysics Modelling ◽  
Ultrasonic Melt Treatment ◽  
Strong Segregation

This study concerns the numerical simulation of two competing ultrasonic treatment (UST) strategies for microstructure refinement in the direct-chill (DC) casting of aluminium alloys. In the first, more conventional, case, the sonotrode vibrating at 17.3 kHz is immersed in the hop-top to treat the sump melt pool, in the second case, the sonotrode is inserted between baffles in the launder. It is known that microstructure refinement depends on the intensity of acoustic cavitation and the residence time of the treated fluid in the cavitation zone. The geometry, acoustic field intensity, induced flow velocities, and local temperature are factors which affect this treatment. The mathematical model developed in this work couples flow velocity, acoustics modified by cavitation, heat transfer, and solidification at the macroscale, with Lagrangian refiner particles, used to determine: (a) their residence time in the active zones, and (b) their eventual distribution in the sump as a function of the velocity field. This is the first attempt at using particle models as an efficient, though indirect, alternative to microstructure simulation, and the results indicate that UST in the launder, assisted with baffle separators, yields a more uniform distribution of refining particles, avoiding the strong acoustic streaming jet that, otherwise, accompanies hot-top treatment, and may lead to the strong segregation of refining particles. Experiments conducted in parallel to the numerical studies in this work appeared to support the results obtained in the simulation.

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

2019 ◽  
Vol 54 ◽  
pp. 171-182 ◽  
Author(s):  
G.S. Bruno Lebon ◽  
Georges Salloum-Abou-Jaoude ◽  
Dmitry Eskin ◽  
Iakovos Tzanakis ◽  
Koulis Pericleous ◽  
...  
Keyword(s):  
Numerical Modelling ◽  
Acoustic Streaming ◽  
Direct Chill ◽  
Melt Treatment ◽  
Dc Casting ◽  
Ultrasonic Melt Treatment

scholarly journals Contactless Ultrasonic Treatment in Direct Chill Casting

JOM ◽  
2020 ◽  
Vol 72 (11) ◽  
pp. 4082-4091
Author(s):  
Catherine E. H. Tonry ◽  
Valdis Bojarevics ◽  
Georgi Djambazov ◽  
Koulis Pericleous
Keyword(s):  
Grain Refinement ◽  
Ultrasonic Treatment ◽  
Numerical Models ◽  
Acoustic Streaming ◽  
Acoustic Resonance ◽  
Resonant Mode ◽  
Direct Chill ◽  
Ferrous Alloy ◽  
Melt Pool ◽  
Dc Casting

Abstract Uniformity of composition and grain refinement are desirable traits in the direct chill (DC) casting of non-ferrous alloy ingots. Ultrasonic treatment is a proven method for achieving grain refinement, with uniformity of composition achieved by additional melt stirring. The immersed sonotrode technique has been employed for this purpose to treat alloys both within the launder prior to DC casting and directly in the sump. In both cases, mixing is weak, relying on buoyancy-driven flow or in the latter case on acoustic streaming. In this work, we consider an alternative electromagnetic technique used directly in the caster, inducing ultrasonic vibrations coupled to strong melt stirring. This ‘contactless sonotrode’ technique relies on a kilohertz-frequency induction coil lowered towards the melt, with the frequency tuned to reach acoustic resonance within the melt pool. The technique developed with a combination of numerical models and physical experiments has been successfully used in batch to refine the microstructure and to degas aluminum in a crucible. In this work, we extend the numerical model, coupling electromagnetics, fluid flow, gas cavitation, heat transfer, and solidification to examine the feasibility of use in the DC process. Simulations show that a consistent resonant mode is obtainable within a vigorously mixed melt pool, with high-pressure regions at the Blake threshold required for cavitation localized to the liquidus temperature. It is assumed that extreme conditions in the mushy zone due to cavitation would promote dendrite fragmentation and coupled with strong stirring, would lead to fine equiaxed grains.

Analysis of Microstructural Changes during Pulsed CO2 Laser Surface Processing of AISI 316L Stainless Steel

2011 ◽  
Vol 264-265 ◽  
pp. 1401-1408 ◽  
Author(s):  
Evans Chikarakara ◽  
Sumsun Naher ◽  
Dermot Brabazon
Keyword(s):  
Stainless Steel ◽  
Residence Time ◽  
Laser Processing ◽  
316L Stainless Steel ◽  
Aisi 316L ◽  
Present Contribution ◽  
Aisi 316L Stainless Steel ◽  
Energy Fluence ◽  
Pool Depth ◽  
Melt Pool

In the present contribution, a 1.5kW CO2 laser in pulsed wave mode was used to study the effects of laser processing parameters at specific energy fluence. Cylindrical AISI 316L stainless steel samples rotating perpendicular to the laser irradiation direction were used for these experiments. A surface temperature prediction model was implemented to set the experimental process parameters. Laser processing of AISI 316L steel showed a strong correlation between melt pool depth and the residence time at specific fluence levels. At fixed energy fluence, increase in residence time resulted in growth of the melt pool depth. In the melted region, the microstructure was observed to be of more uniform composition and contain fewer impurities. To improve absorption level, samples were etched and roughened. These samples exhibited lower roughness levels compared to the un-treated samples. For a constant fluence level, samples with improved absorption displayed an increase in depth of melt pool at lower peak powers and higher residence time. As the laser beam interaction time increased, the surface roughness of the steel increased for the various pulse energy levels examined. While the structure of the surface was seen to retain a crystal arrangement, grain orientation changes were observed in the laser processed region.

Industrial Direct Chill Slab Caster of Tin Bronze (C903) Using a Porous Filter in the Hot-Top

2017 ◽  
Vol 10 (2) ◽  
Author(s):  
Mainul Hasan ◽  
Latifa Begum
Keyword(s):  
Contact Region ◽  
Convective Heat Transfer Coefficient ◽  
Direct Chill ◽  
Cfd Modeling ◽  
Mushy Region ◽  
Slab Caster ◽  
Entire Cross Section ◽  
Porous Filter ◽  
Hot Top ◽  
Tin Bronze

A 3D computational fluid dynamics (CFD) modeling study has been carried out for the tin bronze (C903) slab of industrial size in a vertical direct chill caster. The melt is delivered from the top across the entire cross section of the caster. An insulated hot-top is considered above the 80-mm mold to control the melt level in the mold. A porous filter is considered in the hot-top region of the mold to arrest the incoming inclusions and homogenize the flow into the mold. The melt flow through the porous filter is modeled on the basis of the Brinkmann–Forchheimer-extended non-Darcy model. Results are obtained for four casting speeds varying from 40 to 100 mm/min. The metal–mold contact region, as well as the convective heat transfer coefficient at the mold wall, is also varied. In addition to the above, the Darcy number for the porous media is also changed. All parametric studies are performed for a fixed inlet melt superheat of 62 °C. The results are presented pictorially in the form of temperature and velocity fields. The sump depth, mushy region thickness, solid shell thickness (ST) at the exit of the mold, and axial temperature profiles are also presented and correlated with the casting speed through regression analysis.

A cellular automaton simulation of W–Ni alloy solidification in laser solid forming process

2017 ◽  
Vol 02 (04) ◽  
pp. 1750016
Author(s):  
Haiou Yang ◽  
Lei Wei ◽  
Xin Lin
Keyword(s):  
Cellular Automaton ◽  
Laser Remelting ◽  
Dimensional Model ◽  
Forming Process ◽  
Microstructure Simulation ◽  
Melt Pool ◽  
Laser Solid Forming ◽  
Ni Alloy ◽  
Ca Model ◽  
Metallurgy Process

An alloy cellular automaton (CA) model is developed for the microstructure simulation in directional solidification and laser solid forming (LSF) process. The CA model's capture rule was modified by a limited neighbor solid fraction (LNSF) method. A multiscale two-dimensional model is presented for simulating laser remelting process, which is the same as LSF without the addition of metallic powders into melt pool. The metallurgy process in melt pool was simulated, including temperature distribution, pool shape and solidification of microstructure. The microstructure evolution of tungsten–nickel alloy (W–Ni) during LSF is also simulated by present CA model.

Improved VDC Casting of Aluminium Alloys through an Understanding of the Surface Properties of the Molten Metal

2006 ◽  
Vol 519-521 ◽  
pp. 1693-1698
Author(s):  
John A. Taylor ◽  
Ian F. Bainbridge
Keyword(s):  
Surface Properties ◽  
Molten Metal ◽  
Aluminium Alloys ◽  
Defect Formation ◽  
Direct Chill ◽  
Gradual Change ◽  
Liquid Aluminium ◽  
Hot Top ◽  
Metal Head ◽  
Wide Range

Vertical direct chill (VDC) casting of aluminium alloys is a mature process that has evolved over many decades through gradual change to both equipment design and casting practice. Today, air-pressurised, continuous lubrication, hot top mould systems with advanced station automation are selected as the process of choice for producing extrusion billet. Specific sets of operating parameters are employed on these stations for each alloy and size combination to produce optimal billet quality. The designs and parameters are largely derived from past experience and accumulated know-how. Recent experimental work at the University of Queensland has concentrated on understanding the way in which the surface properties of liquid aluminium alloys, e.g., surface tension, wetting angle and oxide skin strength, influence the size and shape of the naturally-stable meniscus for a given alloy, temperature and atmosphere. The wide range of alloyand condition-dependent values measured has led to the consideration of how these properties impact the stability of the enforced molten metal meniscus within the hot top mould cavity. The actual shape and position of the enforced meniscus is controlled by parameters such as the upstream conduction distance (UCD) from sub-mould cooling and the molten metal head. The degree of deviation of this actual meniscus from the predicted stable meniscus is considered to be a key driver in surface defect formation. This paper reports on liquid alloy property results and proposes how this knowledge might be used to better design VDC mould systems and casting practices.

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