Morphological development of solidification structures under forced fluid flow: a Monte-Carlo simulation

Das, A.; Ji, Shouxun; Fan, Z.

doi:10.1016/s1359-6454(02)00305-1

Cited by 81 publications

(59 citation statements)

References 18 publications

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“…As a result of the high shear rate and high intensity of turbulence provided by the twin-screw shearing mechanism, both the temperature and chemical composition of the melt will quickly get smoothed out. According to previous studies, 12,13) this will result in enhanced effective nucleation and spherical growth, and eventually lead to formation of fine and uniform semisolid slurry, as shown in Figs. 3 and 7.…”

Section: Discussionmentioning

confidence: 80%

“…This makes the slurry making process highly efficient because of the rapid heat extraction. In addition, the powerful convection effect inside the slurry maker during solidification leads to obvious grain refinement to the alloy and gives rise to fine, globular primary magnesium particles, 12,13) compared with the coarse dendrites formed in a conventional HPDC process. Thus, in principle, it is anticipated that, application of the RDC process to high zinc content Mg-Zn-Al alloys should be able to further enhance their room-temperature mechanical properties.…”

Section: Introductionmentioning

confidence: 99%

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Microstructure and Mechanical Properties of a Rheo-Diecast Mg–10Zn–4.5Al Alloy

2005

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High zinc content Mg-Zn-Al alloys have the potential to be used as high pressure die casting (HPDC) alloys for applications up to 150 C. However, these alloys show high tendency to hot tearing and microporosity. Rheo-diecasting (RDC) is an innovative semisolid HPDC process, which can effectively eliminate the formation of primary magnesium dendrites and convert them into fine, globular particles. This very positive change in the morphology and distribution of the primary phase reduces the subsequent formation of various casting defects. In this study, a composition of Mg-10Zn-4.5Al was selected from the Mg-Zn-Al system and processed with both HPDC and RDC. It is shown that, samples produced by the RDC process exhibit substantially reduced hot cracks, few gas pores, and a nearly uniform distribution of fine, globular primary particles. These microstructural changes resulted in much improved strength and elongation, which are comparable to those of AZ91D, while the processing temperature is much lower. It is concluded that high zinc content Mg-Zn-Al alloys have good potential to be exploited as commercially useful alloys by the RDC process.

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Section: Discussionmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Microstructure and Mechanical Properties of a Rheo-Diecast Mg–10Zn–4.5Al Alloy

2005

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“…The numerical analysis indicated that the growth morphology may change from equiaxed dendrite to spheroid via rosette when shear rate and turbulence increases significantly. Das et al [13], using Monte Carlo simulations, showed that a tendency for dendritic growth was reduced and globularization of the primary phase in the melt is caused by the rotation of the solid particle and elimination of constitutional undercooling through reduction of the thermal/solutal diffusion layers at the solid-liquid interface.…”

Section: Spheroidsmentioning

confidence: 99%

Microstructural Evolution in AlMgSi Alloys during Solidification under Electromagnetic Stirring

Mikołajczak

2017

Metals

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Equiaxed solidification of AlMgSi alloys with Fe and Mn was studied by electromagnetic stirring to understand the effect of forced flow. The specimens solidified with a low cooling rate, low temperature gradient, and forced convection. Stirring induced by a coil system around the specimens caused a transformation from equiaxed dendritic to rosette morphology with minor dendrites and, occasionally, spheroids. This evolution was quantitatively observed with specific surface S v . The precipitation sequence of the phases was calculated using the CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) technique. Melt flow decreased secondary dendrite arm spacing λ 2 in the AlSi5Fe1.0 alloy, while λ 2 increased slightly in Mg-containing alloys. The length of detrimental β-Al 5 FeSi phases decreased only in AlSi5Fe1.0 alloy under stirring, whereas in Mg-containing alloys, changes to the β-Al 5 FeSi phase were negligible; however, in all specimens, the number density increased. The modification of Mn-rich phases, spacing of eutectics, and Mg 2 Si phases was analyzed. It was found that the occurrence of Mg 2 Si phase regions reduced fluid flow in the late stages of solidification and, consequentially, reduced shortening of β-Al 5 FeSi, diminished secondary arm-ripening caused by forced convection, and supported diffusive ripening. However, the Mg 2 Si phase was found to have not disturbed stirring in the early stage of solidification, and transformation from dendrites to rosettes was unaffected.

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“…[48,49] Forced flow reduces essentially the solute diffusion layer at the solid liquid interface, and thus reduces the region and amount of constitutional undercooling and affects the evolution of the dendritic morphology in the mush. [50] Stirring, and thus solute transport, could even generate fragmentation of the dendrites accompanied by dendrite arm root remelting or dissolution due to solute transport. [35,[51][52][53] The fluid flow, as used here, has been confirmed to reduce the primary stem spacing and increase the SDAS.…”

Section: The Phenomenon Of B-al 5 Fesi Phases Shorteningmentioning

confidence: 99%

Interplay Between Melt Flow and the 3D Distribution and Morphology of Fe-Rich Phases in AlSi Alloys

Mikołajczak

Ratke

2014

Metall Mater Trans A

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The presence of Fe aids in establishing the mechanical and physical properties of AlSi alloys and is also one of the main impurities leading to formation of b-Al 5 FeSi intermetallics. This study aims to understand the effect of fluid flow on the dendritic microstructure with intermetallics in Al-5/7/9 wt pct Si-0.2/0.5/1.0 wt pct Fe alloys that are directionally solidified under defined thermal and fluid flow conditions. We made extensive use of 3D X-ray tomography to obtain a better insight into the morphology and formation of the intermetallics. Three-dimensional (3-D) distribution of intermetallics presented here shows that the growth of large b-Al 5 FeSi due to forced flow occurs in the eutectic specimen center and together with an increase in the number density of b precipitates. The 3D reconstructions have verified the b shaped to be curved, bent with twining, branched, and to have imprints, holes, and propeller-shaped platelets. The 3D views showed that hole-shaped b arose from the lateral growth around a-Al dendrites. These views also confirmed the phenomenon of shortening of b as an effect of flow in the dendritic region, where b could be fragmented or completely remelted, and ultimately resulting in microstructures with shorter b-Al 5 FeSi and increases in number density. The analysis revealed an interaction between melt flow, 3D distribution, and the morphology of b-Al 5 FeSi. The growth of a large and complex group of b intermetallics can reduce the melt flow between dendrites and strengthen pore nucleation and eutectic colonies nucleation, leading to lower permeability of the mushy zone and increased porosity in the castings.

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Morphological development of solidification structures under forced fluid flow: a Monte-Carlo simulation

Cited by 81 publications

References 18 publications

Microstructure and Mechanical Properties of a Rheo-Diecast Mg–10Zn–4.5Al Alloy

Microstructure and Mechanical Properties of a Rheo-Diecast Mg–10Zn–4.5Al Alloy

Microstructural Evolution in AlMgSi Alloys during Solidification under Electromagnetic Stirring

Interplay Between Melt Flow and the 3D Distribution and Morphology of Fe-Rich Phases in AlSi Alloys

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Morphological development of solidification structures under forced fluid flow: a Monte-Carlo simulation

Cited by 81 publications

References 18 publications

Microstructure and Mechanical Properties of a Rheo-Diecast Mg&ndash;10Zn&ndash;4.5Al Alloy

Microstructure and Mechanical Properties of a Rheo-Diecast Mg&ndash;10Zn&ndash;4.5Al Alloy

Microstructural Evolution in AlMgSi Alloys during Solidification under Electromagnetic Stirring

Interplay Between Melt Flow and the 3D Distribution and Morphology of Fe-Rich Phases in AlSi Alloys

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Microstructure and Mechanical Properties of a Rheo-Diecast Mg–10Zn–4.5Al Alloy

Microstructure and Mechanical Properties of a Rheo-Diecast Mg–10Zn–4.5Al Alloy