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.

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 Melt Conditioned Direct Chill Casting (MC-DC) Process for Production of High Quality Aluminium Alloy Billets

2014 ◽  
Vol 794-796 ◽  
pp. 149-154 ◽  
Author(s):  
Jayesh B. Patel ◽  
Hu Tian Li ◽  
Ming Xu Xia ◽  
Simon Jones ◽  
Sundaram Kumar ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Aluminium Alloy ◽  
Casting Process ◽  
Direct Chill ◽  
High Shear ◽  
Uniform Temperature ◽  
High Quality ◽  
Dispersed Particles ◽  
Refined Microstructure ◽  
Dc Casting

A novel direct chill (DC) casting process, melt conditioned direct chill (MC-DC) casting process, has been developed for production of high quality aluminium alloy 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 nucleating 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. Experimental results have demonstrated that, the MC-DC casting process can produce aluminium alloy billets with significantly refined microstructure and reduced cast defects. In this paper, we give an overview of the MC-DC casting process and report on results obtained from an industrial scale trial.

Modelling of the Metal/Mould Interactions in the DC Casting Process for Aluminium and Magnesium

2010 ◽  
Vol 654-656 ◽  
pp. 783-786 ◽  
Author(s):  
Arvin Prasad ◽  
Ian F. Bainbridge
Keyword(s):  
Heat Transfer ◽  
Casting Process ◽  
Direct Chill ◽  
Heat Extraction ◽  
Small Scale ◽  
Wall Region ◽  
Wall Heat Transfer ◽  
Mould Wall ◽  
Dc Casting ◽  
Basic Features

The process of direct chill (DC) casting of aluminium and magnesium alloys is regarded as a mature technology. The thrust of more recent work to understand and upgrade the technology has been centred on developing models of the process, the most advanced of which (e.g., Alsim and Calcasoft) have been used to examine what may be considered macro-features of the process (macro-segregation, hot cracking, etc.). These models, being macroscopic, rarely elaborate on the role of mould-wall heat transfer in the DC casting process. As part of the work on DC casting being conducted at CAST, for the investigation of small scale features of the process (e.g. heat extraction through the mould wall), a 2D finite Difference model of the process near the mould-wall region has been developed. The basic features of the model are described and initial results outlined.In particular, the effect of mould-wall heat transfer on the solid shell formed during the steady state regime of DC casting will be presented.

Application Research of a New Coupling Stirring on DC Casting Process for Large-Sized Aluminum Ingots

2015 ◽  
Vol 817 ◽  
pp. 48-54 ◽  
Author(s):  
Hai Jun Wang ◽  
Jun Xu ◽  
Zhi Feng Zhang ◽  
Bo Liang ◽  
Ming Wei Gao
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Casting Process ◽  
Direct Chill ◽  
Application Research ◽  
Center Position ◽  
Composition Segregation ◽  
Dc Casting ◽  
The Difference ◽  
7075 Alloy

A new coupling stirring technology was proposed and used to prepare direct chill (DC) ingots. Ingots of 7075 alloy were produced by a process of normal direct chill (NDC) casting and coupling-stirring direct chill (CDC) casting, respectively. The effect of the technology on the microstructures, composition segregation and mechanical properties of the ingots was investigated. The results showed that the temperature variation in the CDC casting process was more uniform than that in the NDC casting process. The grain of the CDC ingots was finer and more spherical than the grain of NDC ingots. The grain size at the edge, 1/2 radius, and center position in CDC ingot decrease by 28%, 22%, and 24% comparing with the grain size of the corresponding positions of NDC ingot, respectively. The billets with higher performance and lower macro-segregation were obtained in case of CDC. The flow stresses and the difference in different positions of DC ingots measured at Gleeble-1500D thermo-mechanical simulator decreased obviously when the coupling stirring technology is used in the casting process.

A Comparison Between 3-D Thermal Model and 3-D CFD Model for Vertical DC Casting of Rolling Ingots of Aluminum Alloy 7050

2014 ◽  
Author(s):  
Mainul Hasan ◽  
Latifa Begum
Keyword(s):  
Heat Transfer ◽  
Aluminum Alloy ◽  
Thermal Model ◽  
Casting Process ◽  
Direct Chill ◽  
Turbulent Heat Transfer ◽  
Mushy Region ◽  
Turbulent Heat ◽  
Cfd Model ◽  
Dc Casting

In this study, first a 3-D thermal model is developed for an open top, vertical direct chill (DC) casting process of rolling slabs (ingots) by taking into account the casting speed in the form of slag flow in the thermal connective-diffusion equation. The mushy region solidification characteristics of the process are accounted for through the implementation of the enthalpy porosity technique. The thermal model is later extended to a 3-D CFD model to account for the coupled turbulent heat transfer and solidification aspect of the process. Both models simulate an industrial-sized, hot-top type vertical Direct Chill (DC) slab caster for high strength aluminum alloy AA-7050. A staggered control volume based finite-difference scheme is used to solve the modeled equations and the associated boundary conditions. In the CFD model, the turbulent aspects of flow and solidification heat transfer are modeled using a low Reynolds number version of the k–ε eddy viscosity approach. Computed results for the steady-state phase of the casting process are presented for four casting speeds varying from 60 to 180 mm/min for a fixed inlet melt superheat of 32°C. Simulation results of the velocity and temperature fields and heat fluxes along the caster surface are presented for the CFD model and the shell thickness and sump depth are compared between the CFD and thermal models.

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.

Effect of Advanced Cooling Front (ACF) Phenomena on Film Boiling and Transition Boiling Regimes in the Secondary Cooling Zone during the Direct-Chill Casting of Aluminium Alloys

2006 ◽  
Vol 519-521 ◽  
pp. 1687-1692 ◽  
Author(s):  
Etienne J.F.R. Caron ◽  
Mary A. Wells
Keyword(s):  
Heat Flux ◽  
Heat Flux Density ◽  
Heat Removal ◽  
Casting Process ◽  
Direct Chill ◽  
Film Boiling ◽  
Cooling Zone ◽  
Secondary Cooling ◽  
Secondary Cooling Zone ◽  
Dc Casting

Accurate knowledge of the boundary conditions is essential when modeling the Direct-Chill (DC) casting process. Determining the surface heat flux in the secondary cooling zone, where the greater part of the heat removal takes place, is therefore of critical importance. Boiling water heat transfer phenomena are quantified with boiling curves which express the heat flux density as a function of the surface temperature. Compilations of boiling curves for the DC casting of aluminum alloys present a good agreement at low surface temperatures but a very poor agreement at higher surface temperatures, in the transition boiling and film boiling modes. Secondary cooling was simulated by spraying instrumented samples with jets of cooling water. Quenching tests were conducted first with a stationary sample, and then with a sample moving at a constant “casting speed” in order to better simulate the DC casting process. The ejection of the water film in quenching tests with a stationary sample and the relative motion between the sample and the water jets both lead to an Advanced Cooling Front (ACF) effect, in which cooling occurs through axial conduction within the sample rather than through boiling water heat transfer at the surface. The heat flux density and surface temperature were evaluated using the measured thermal history data in conjunction with a two-dimensional inverse heat conduction (IHC) model. The IHC model developed at the University of British Columbia was able to take into account the advanced cooling front effect. The effect of various parameters (initial sample temperature, casting speed, water flow rate) on the rate of heat removal in the film boiling and transition boiling regimes was investigated.

Solidification Mechanisms in Melt Conditioned Direct Chill (MC-DC) Cast AZ31 Billets

2013 ◽  
Vol 765 ◽  
pp. 291-295 ◽  
Author(s):  
Ming Xu Xia ◽  
A.K. Prasada Rao ◽  
Zhong Yun Fan
Keyword(s):  
Solidification Front ◽  
Casting Process ◽  
Direct Chill ◽  
Melt Flow ◽  
Metallographic Examination ◽  
Dc Casting ◽  
Solidification Mechanism

The solidification mechanism in the melt conditioned direct chill (MC-DC) casting process was investigated by pouring liquid Pb into the sump during the casting process. This preserved the solidification front for subsequent metallographic examination. The results demonstrated that the solidification in the MC-DC casting process was preceded by the sedimentation of rosettes, which were nucleated in the sump and then grew under intensive melt flow.

Effect of Casting Velocity on Microstructures of Almg0.9Si0.7 Alloy by Low-Superheat DC Casting

2011 ◽  
Vol 415-417 ◽  
pp. 549-552 ◽  
Author(s):  
Da Zhi Zhao ◽  
Fu Xiao Yu ◽  
Fang Liu ◽  
Ke Zhun He
Keyword(s):  
Dendritic Growth ◽  
Smooth Surface ◽  
Casting Process ◽  
Direct Chill ◽  
Pouring Temperature ◽  
Suitable Temperature ◽  
Dc Casting ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Low Superheat

The billets of AlMg0.9Si0.7 alloy, which were cast through the direct chill (DC) casting process of low superheat, were analyzed to study the effect of casting velocity on the surface quality and the morphology of primary α grains. The results show that the nucleating quantity of primary α grains in the melt is increased obviously due to the low pouring temperature during DC casting of low superheat. The suitable temperature gradient in front of the solid-liquid interface is obtained by changing the casting velocity, and the dendritic growth of the primary α grains is inhibited effectively. The billet of AlMg0.9Si0.7 alloy with smooth surface and homogeneous, fine rosette-shaped grains is obtained at the velocity of 130mm/min.

Evolution of the Retrogression and Reaging Treatment on Microstructure and Properties of Aluminum Alloy (Al-Zn-Mg-Cu)

2014 ◽  
Vol 925 ◽  
pp. 258-262 ◽  
Author(s):  
Haider T. Naeem ◽  
Khairul R. Ahmad ◽  
Kahtan S. Mohammad ◽  
Azmi Rahmat
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Treatment Process ◽  
Casting Process ◽  
Direct Chill ◽  
Cu Alloys ◽  
Treatment Conditions ◽  
Retrogression And Reaging ◽  
Aa 7075 ◽  
Dc Casting

In this study the evolution of the retrogression and reaging (RRA) heat treatment process on microstructure and mechanical properties of AA 7075 Al-alloys which produced by semi-direct chill (DC) casting process were investigated. Al-Zn-Mg-Cu alloys were homogenized at different heat treatment conditions, aged at 120°C for 24 h (T6), and retrogressed at 180°C for 30 min then re-aged at 120°C for 24 h (RRA). The results showed that this three-step process of the heat treatments, the mechanical properties of alloys was substantially improved. The highest ultimate tensile strength and Vickers hardness attained for the retrogression and re-aging about 530 MPa and 223 HV respectively. The precipitation strengthening is responsible about improve the strength under impact the retrogression and re-aging process.

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