Rheological behaviour of partially solidified aluminium matrix composites

Quaak, C.J.; Horsten, M.G.; Kool, W. H.

doi:10.1016/0921-5093(94)90909-1

Cited by 40 publications

(44 citation statements)

References 8 publications

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“…Included in the figure is the steadystate viscosity determined by Quaak [47] for a 7% Si aluminium alloy, extrapolated to 0.5 fraction solid; this is well below the other results, emphasizing that the steady state is not achieved in those experiments, nor in industrial thixoforming.…”

Section: Rapid Compressionmentioning

confidence: 85%

“…The work of Liu et al [86] involves the fastest data collection rate so far (~1 kHz capture rate). This is significantly faster than that used by other workers (200 Hz in [79], 9 Hz in [47], 200 Hz in [80]) and enables the capture of the very fast process. The results for shear rate jumps from 0 to 100 s -1 after different rest times are shown in Fig.19.…”

Section: Rapid Shear Rate Changes In Rheometersmentioning

confidence: 90%

“…Previous reviews include those by Kenney et al [14], Flemings [45], Kirkwood [2], Quaak [47], Collot [53] and Fan [12]. In addition, a book has recently been published edited by Figueredo [29].…”

Section: Disadvantagesmentioning

confidence: 99%

“…Peng and Wang [80] observed that the overshoot increases with increasing solid fraction. Horsten et al [87] and Quaak and co-workers [40,47] argued that during this transient period structure evolution has not had time to occur and the structure corresponds to that of the previous shear rate. Kumar et al [88] and Koke and Modigell [66] however, find shear thickening 'iso-structural' flow behaviour (e.g.…”

Section: Rapid Shear Rate Changes In Rheometersmentioning

confidence: 99%

“…This would be expected, as the breaking up of 'bonds' between spheroidal solid particles in agglomerates is likely to be easier than the formation of bonds during shear-rate drops. Quaak [47] proposes two characteristic times to describe a shear rate jump. He suggests that during a shear-rate change, the slurry undergoes an initial rapid breakdown/buildup followed by a more gradual process dependent on diffusion.…”

Section: Transient Behaviour Of Semi-solid Alloysmentioning

confidence: 99%

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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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Section: Rapid Compressionmentioning

confidence: 85%

Section: Rapid Shear Rate Changes In Rheometersmentioning

confidence: 90%

Section: Disadvantagesmentioning

confidence: 99%

Section: Rapid Shear Rate Changes In Rheometersmentioning

confidence: 99%

Section: Transient Behaviour Of Semi-solid Alloysmentioning

confidence: 99%

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Modelling the Semisolid Processing of Metallic Alloys

Atkinson

2005

ChemInform

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Response of semi-solid Sn-15 pct Pb to rapid shear-rate changes

Liu

Ward

Atkinson

et al. 2003

Metall Mater Trans A

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Semisolid metal alloys, used in thixoforming, are thixotropic. The slurry viscosity is shear-rate-and time dependent provided the microstructure in the semisolid state is nondendritic and consists of solid spheroids surrounded by liquid. Thixoforming takes less than 1 second, during which time the structure of the material breaks down. This breakdown can be studied by viscometry, using rapid data-collection rates, by imposing rapid increases in shear rate on the slurry. An initial rapid (Ͻ 1 second) structural breakdown during a shear-rate jump is followed by a more gradual decrease in viscosity, lasting several minutes. The slurry breaks down more rapidly with a higher final shear rate, but the first breakdown time is independent of the initial shear rate. The reverse is found with the shear-rate drops: recovery times increase with increasing final shear rate. Again, this time is independent of the starting shear rate. The shear stress and viscosity during initial breakdown and initial recovery can be described by single exponential equations. Build-up processes were examined by performing jumps after allowing the slurry to rest at a zero shear rate for different times. The increase in peak stress with rest time reflects the evolving degree of particle agglomeration. Microstructural examination confirms this phenomenon.

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Experimental Investigation on the Rheological Behavior of Hypereutectic Al-Si Alloys by a Precise Rotational Viscometer

Heidary

Akhlaghi

2010

Metall Mater Trans A

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Determining the viscosity of low solid volume fraction semisolid alloys is important for predicting the gradient of primary particles within functionally graded materials (FGMs), produced by in-situ casting processes. In this study, a new precise rotational viscometer was developed and used to measure the viscosity of Al-22 pct Si and Al-30 pct Si semisolid alloys up to solid volume fractions of 9 and 20 pct, respectively. Three kinds of typical curves, viscosity (g) vs solid volume fraction (f s ), shear time (t), and shear rate (_ c), were derived from the results of viscosity measurements for both Al-Si alloys. In the semisolid Al-Si alloys, thixotropic behavior was not detected at low solid volume fractions, but this behavior was obviously observed with increasing solid volume fraction and could be described by an analytical model. Finally, the results showed that the equilibrium viscosity of the semisolid alloys with thixotropic properties decreased by increasing shear rate according to the Ostwald-De Waele power law. A special test, developed in this research, was used to show the effect of agglomeration on the viscosity of the semisolid alloys.

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Rheological behaviour of partially solidified aluminium matrix composites

Cited by 40 publications

References 8 publications

Modelling the Semisolid Processing of Metallic Alloys

Modelling the Semisolid Processing of Metallic Alloys

Response of semi-solid Sn-15 pct Pb to rapid shear-rate changes

Experimental Investigation on the Rheological Behavior of Hypereutectic Al-Si Alloys by a Precise Rotational Viscometer

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