Thixotropic rheology of semisolid metal suspensions

Burgos, Gilmer R.; Alexandrou, Andreas N.; Entov, V. M.

doi:10.1016/s0924-0136(00)00731-7

Cited by 78 publications

(60 citation statements)

References 4 publications

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“…[30] Kumar et al [23,27] and Koke and Modigell [25,28] (with further analysis of Reference 28 by Burgos et al [29] ) find their material to be shear thickening during the transient, Quaak [22] and Liu et al [24] observe the material is shear thinning. Peng and Wang [26] study the behavior but do not state a conclusion.…”

Section: F Aim Of the Papermentioning

confidence: 98%

“…There is contradictory evidence in the literature [22][23][24][25][26][27][28][29] as to whether the behavior during rapid increases in shear rate is shear thinning or shear thickening, although it is clear that once in the die the material is thinning. [30] Kumar et al [23,27] and Koke and Modigell [25,28] (with further analysis of Reference 28 by Burgos et al [29] ) find their material to be shear thickening during the transient, Quaak [22] and Liu et al [24] observe the material is shear thinning.…”

Section: F Aim Of the Papermentioning

confidence: 99%

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Does Shear Thickening Occur in Semisolid Metals?

Atkinson

Favier

2016

Metall Mater Trans A

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In the various forms of semisolid processing such as thixoforming and thixoforging, the entry into the die occurs in a fraction of a second so it is the transient rheological behavior which governs the initial stages of flow. In experiments in the literature, this rheological behavior is probed through applying rapid transitions in shear rate under isothermal conditions. There is contradictory evidence as to whether the behavior during these transitions is shear thinning or shear thickening, although it is clear that once in the die the material is thinning. Here the data in the literature are reanalyzed to obtain a rationalization of the contradictions which has not previously been available. It is argued that if a suspension is initially in a disagglomerated state (i.e., one which is initially sheared), the instantaneous behavior with a jump-up in shear rate is shear thickening (even if the long-term steady-state behavior is shear thinning) provided the fraction solid is greater than about 0.36 and the final shear rate at the end of the jump is greater than about 100 s À1 . If the jump-up in shear rate is made from rest then yield masks the shear thickening.

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Section: F Aim Of the Papermentioning

confidence: 98%

Section: F Aim Of the Papermentioning

confidence: 99%

Does Shear Thickening Occur in Semisolid Metals?

Atkinson

Favier

2016

Metall Mater Trans A

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“…In Burgos et al [108], the Herschel-Bulkley model in equation (33) in Table 5 and the approach of the previous papers [105][106][107] is expanded to include the effect of the evolution of microstructure via an equation for t ∂ ∂λ very similar to equation (15) in fact, a way of introducing two relaxation processes as in Quaak [47]). In addition, the yield stress, consistency index K and power law index n are now all assumed to be functions of the volume fraction solid s f and the structural parameter λ .…”

Section: Alexandrou Burgos and Co-workersmentioning

confidence: 99%

“…Burgos et al [108] obtain these using data on Sn-15%Pb from Modigell et al [133]. The behaviour of the material is shear thickening for isostructure during a shear rate jump.…”

Section: Alexandrou Burgos and Co-workersmentioning

confidence: 99%

Modelling the Semisolid Processing of Metallic Alloys

Atkinson

2005

ChemInform

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Semi-solid processing of metallic alloys and composites utilises the thixotropic behaviour of materials with non-dendritic microstructure in the semi-solid state. The family of innovative manufacturing methods based on this behaviour has been developing over the last twenty years or so and originates from scientific work at MIT in the early 1970s. Here, a summary is given of:-routes to spheroidal microstructures; types of semi-solid processing; and advantages and disadvantages of these routes.Background rheology and mathematical theories of thixotropy are then covered as precursors to the main focus of the review on transient behaviour of semi-solid alloy slurries and computational modelling. Computational Fluid Dynamics (CFD) can be used to predict die filling. However, some of the reported work has been based on rheological data obtained in steady state experiments, where the semi-solid material has been maintained at a particular shear rate for some time. In reality, in thixoforming, the slurry undergoes a sudden increase in shear rate from rest to 100s -1 or more as it enters the die. This change takes place in less than a second. Hence, measuring the transient rheological response under rapid changes in shear rate is critical to the development of modelling of die filling and successful die design for industrial processing. The modelling can be categorised as one phase or two phase and as finite difference or finite element. Recent work by Alexandrou and co-workers and, separately Modigell and co-workers, has led to the production of maps which, respectively summarise regions of stable/unstable flow and regions of laminar/transient/turbulent fill. These maps are of great potential use for the prediction of appropriate process parameters and avoidance of defects. A novel approach to modelling by Rouff and coworkers involves micro-modelling of the 'active zone' around spheroidal particles.There is little quantitative data on the discrepancies or otherwise between die fill simulations and experimental results (usually obtained through interrupted filling).There are no direct comparisons of the capabilities of various software packages to model the filling of particular geometries accurately. In addition, the modelling depends on rheological data and this is sparse, particularly for the increasingly complex two-phase models. Direct flow visualisation can provide useful insight and avoid the effects of inertia in interrupted filling experiments.

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“…Burgos et al represent the K as time dependent factor in semisolid behavior, when all the solid particles are connected, K=1 and none of the particles are connected, K=0 [18]. Based on the predicted temperature, the yield stress (τ 0 )…”

Section: The Effect Of Temperature and Speed Of Mixing On Thixomixingmentioning

confidence: 99%

Microstructure and properties of aluminum silicon/short fibre carbon composites fabricated by semi-solid thixomixing

2015

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A novel method was developed, based on thixotropic nature of semi-solid slurry of aluminum silicon alloy, for the effective dispersion and distribution of short carbon fibers (C sf ) under intensive shear stress (τ) into the eutectic without physical or chemical damage.The C sf were distributed homogeneously into the matrix at optimum conditions: a temperature of 576-580 °C, around 48% of solid fraction, and rotation speed of mixing was at 100 rpm. The gas entrapment and porosity was a challenge in the fabrication the aluminum composite by thixomixing, and its size increased when the samples were heat treated. The extruded and heat treated composites had around 24% improvement of mechanical strength as assessed by tensile tests. The predominant deposition of silicon and its intermetallics at the interfacial region improved the wettability and adherence to achieve good mechanical properties. The formation of some intermetallics can be helpful to overcome low wettability effects and their structural evolutions were impressive. The fractography analysis illustrated the ductile fracture with some plastic deformation as the results of dimples and some fiber pull-out in the fractured surface. Ultra-micro hardness evaluation showed good interfacial bonding after heat treatment. The thixomixing process can be developed to produce various composites with different reinforcement.

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Thixotropic rheology of semisolid metal suspensions

Cited by 78 publications

References 4 publications

Does Shear Thickening Occur in Semisolid Metals?

Does Shear Thickening Occur in Semisolid Metals?

Modelling the Semisolid Processing of Metallic Alloys

Microstructure and properties of aluminum silicon/short fibre carbon composites fabricated by semi-solid thixomixing

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