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.

Microstructures of DC Cast Light Alloys under the Influence of Intensive Melt Shearing

2011 ◽  
Vol 690 ◽  
pp. 137-140 ◽  
Author(s):  
Yu Bo Zuo ◽  
Bo Jiang ◽  
Zhong Yun Fan
Keyword(s):  
Grain Refinement ◽  
Heterogeneous Nucleation ◽  
Solidification Process ◽  
Casting Process ◽  
Direct Chill ◽  
Light Alloy ◽  
High Quality ◽  
Light Alloys ◽  
Refined Microstructure ◽  
Dc Casting

A new direct chill (DC) casting process, melt conditioned DC (MC-DC) process has been developed for production of high quality ingots and billets of light alloys. In the MC-DC casting process, intensive melt shearing provided by a newly developed rotor-stator unit is used to control the solidification process during the DC casting with a conventional DC caster. Experimental results of DC casting of Al- and Mg-alloys with and without intensive melt shearing have demonstrated that the MC-DC casting process can produce light alloy billets with significantly refined microstructure and substantially reduced cast defects. The effect of intensive melt shearing on grain refinement has been mainly attributed to the enhanced heterogeneous nucleation on well dispersed oxides occurring naturally in the alloy melt.

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 CFD Simulation Based Investigation of Cavitation Dynamics during High Intensity Ultrasonic Treatment of A356

Metals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1529
Author(s):  
Eric Riedel ◽  
Niklas Bergedieck ◽  
Stefan Scharf
Keyword(s):  
Ultrasonic Treatment ◽  
High Intensity ◽  
Aluminium Alloys ◽  
Cfd Simulation ◽  
Numerical Models ◽  
Acoustic Streaming ◽  
Industrial Applications ◽  
Software Environment ◽  
Wide Range ◽  
Semi Solid

Ultrasonic treatment (UST) and its effects, primarily cavitation and acoustic streaming, are useful for a high range of industrial applications, e.g., welding, filtering, cleaning or emulsification. In the metallurgy and foundry industry, UST can be used to modify a material’s microstructure by treating metal in the liquid or semi-solid state. Cavitation (formation, pulsating growth and implosion of tiny bubbles) and its shock waves, released during the implosion of the cavitation bubbles, are able to break forming structures and thus refine them. In this context, especially aluminium alloys are in the focus of the investigations. Aluminium alloys, e.g., A356, have a significantly wide range of industrial applications in automotive, aerospace and machine engineering, and UST is an effective and comparatively clean technology for its treatment. In recent years, the efforts for simulating the complex mechanisms of UST are increasing, and approaches for computing the complex cavitation dynamics below the radiator during high intensity ultrasonic treatment have come up. In this study, the capabilities of the established CFD simulation tool FLOW-3D to simulate the formation and dynamics of acoustic cavitation in aluminium A356 are investigated. The achieved results demonstrate the basic capability of the software to calculate the above-mentioned effects. Thus, the investigated software provides a solid basis for further development and integration of numerical models into an established software environment and could promote the integration of the simulation of UST in industry.

Microstructure Evolution in Melt Conditioned Direct Chill (MC-DC) Casting of Fe-Rich Al-Alloy

2014 ◽  
Vol 1019 ◽  
pp. 90-95 ◽  
Author(s):  
H.R. Kotadia ◽  
J.B. Patel ◽  
H Tian Li ◽  
F. Gao ◽  
Z. Fan
Keyword(s):  
Grain Refinement ◽  
Microstructure Evolution ◽  
Morphological Evolution ◽  
Casting Process ◽  
Direct Chill ◽  
Al Alloy ◽  
Complete Suppression ◽  
High Quality ◽  
Dc Casting ◽  
Columnar Grain

In order to fabricate high quality aluminium products, it is first essential to produce high quality billets/slabs. One of the key objectives associated with casting processes is to be able to control the as-cast structure. A novel direct chill (DC) casting process, the melt conditioned direct chill (MC-DC) casting process, has been developed for production of high quality aluminium billets. In the MC-DC casting process, a high shear device is submerged in the sump of the DC mould to provide intensive melt shearing, which in turn, disperses potential nucleation particles, creates a macroscopic melt flow to uniformly distribute the dispersed particles, and maintains a uniform temperature and chemical composition throughout the melt in the sump. The effect of intensive shearing on the complex microstructure evolution observed after MC-DC is explained on the basis of nucleation and growth behavior. Complete suppression of typical columnar grain growth and significant equiaxed grain refinement is observed. The solidification mechanisms responsible for the significant grain refinement by intensive shearing and the morphological evolution of Mg2Si and Fe–containing intermetallic phases are discussed.

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 A Study on the Effect of Ultrasonic Treatment on the Microstructure of Sn-30 wt.% Bi Alloy

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1870
Author(s):  
Shuo Wang ◽  
Jinwu Kang ◽  
Xiaopeng Zhang ◽  
Zhipeng Guo
Keyword(s):  
Ultrasonic Treatment ◽  
Acoustic Streaming ◽  
Eutectic Structure ◽  
Eutectic Phase ◽  
Ultrasonic Cavitation ◽  
Mixed Effect ◽  
Temperature Range ◽  
Different Temperatures

The effect of ultrasonic treatment on the microstructure of Sn-30 wt.% Bi alloy was studied at different temperatures. Results showed that the ultrasonic treatment could effectively refine the microstructure of Sn-30 wt.% Bi alloy at a temperature range between the liquidus and solidus. Application of the ultrasound could fragment the primary Sn dendrites during solidification due to a mixed effect of ultrasonic cavitation and acoustic streaming. The divorced eutectic formed when the ultrasonic treatment was applied for the whole duration of the solidification. The eutectic phase grew and surrounded the primary Sn dendrite, and pure Bi phase grew in between the Sn dendritic fragments. The mechanism of the fragmentation of dendrites and the divorced eutectic structure by ultrasonic treatment was discussed.

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