Rheological Behavior Of Semisolid Slurry Research Articles

Rheological modeling and simulation of semi-solid slurry based on experimental study

The rheological behavior of semi-solid slurry is systematically studied via three different testing modes under either shear stress or shear rate control mode. Then the non-Newtonian constitutive parameters, consistency coefficient k and power-law index n, are determined by using Power-Law (PL) and Herschel-Bulkley (HB) models. Results indicate that the viscosity curve from the shear stress control test is more suitable for the PL model fitting and numerical simulation. This investigation not only provides important insights into the rheological characteristics of slurry during semi-solid die casting but also offers a new modeling strategy for non-Newtonian fluid flow.

The Influence of Strontium on Microstructural and Rheological Behavior of the Semi-solid A380 Aluminum Alloy

This article aims to correct the lack of information regarding the combined effect of grain refinement and strontium modification on the microstructure and rheological behavior of semi-solid slurries. The A380 aluminum alloy was studied in the semi-solid state in three different conditions: as received, grain refined and grain refined/modified with Sr. To determine the semi-solid temperature, a DSC analysis and Thermo-calc® simulations were used. SEM, optical and polarized light microscopy analyses were performed to analyze the microstructural changes caused by the refiner and modifier agents as well as to evaluate the morphological evolution of the alloys in the semi-solid state. The rheological behavior was studied with a hot compression test between parallel plates. The main results show that the addition of Sr, besides its influence on the Si and Fe-β particles, also leads to a better globularization of α-Al phase particles in the semi-solid state. Furthermore, the rheological analysis of stress vs strain and apparent viscosity vs average shear rate also point to a better behavior of the alloy in the semi-solid state after Sr modification, thus indicating that Sr addition could improve the performance of the A380 alloy as a semi-solid feedstock.

Influence of time evolution of particle shape on rheological behavior of semisolid slurries of magnesium alloy AZ91D

To gain the insights into the influence of the morphology of solid particles on rheological behavior of semisolid metal slurries, the time evolution of Hausdorff dimensionality describing the particle morphology is deduced in order to quantitatively analyze the time evolution of the particle morphology. In consideration of the role of the liquid entrapped by non-spherical solid particles, the non-spherical solid particles with the entrapped liquid are treated as spherical solid particles, and the equivalent solid volume fraction is defined as the sum of solid volume fraction and the volume fraction of the entrapped liquid. This model could be used to analyze the rheological behavior of the semisolid metal slurries containing the non-spherical particles with Hausdorff dimensionality less than 3. Moreover, the rheological behavior of semisolid magnesium alloy AZ91D is theoretically analyzed by this model during isothermal shearing and continuous cooling. The calculated results are found coinciding with the experimental results and the calculated results also reveal that the shear rate and cooling rate could influence the rheological behavior of semisolid metal slurries by changing the morphology of solid particles except by affecting agglomeration degree.

Theoretical research on rheological behavior of semisolid slurry of magnesium alloy AZ91D

Abstract This paper focuses on the time evolution of the microstructure of liquid-like semisolid metal slurries and provides a model to investigate the origins of pseudoplasticity and thixotropy of semisolid metal slurries. The model could not only be used to predict the steady-state apparent viscosity but also to further elucidate the instantaneous rheological behavior of the semisolid metal slurry with a time-dependent solid volume fraction and a time-dependent shear rate, and it is successfully applied to analyze the rheological behavior of the semisolid slurry of magnesium alloy AZ91D. The calculated results point out that the specific rheological behavior of semisolid metal slurries roots in the time evolution of their microstructure, while the external flow conditions influence the rheological behavior of semisolid metal slurries by changing their microstructure. Furthermore, the calculated results also indicate that the stir’s braking from a certain steady state will lead to further agglomeration and the agglomeration degree will be aggravated during remelting semisolid metal billets.

Rheological Characterization of Semi-Solid A356 Aluminium Alloy

Rheological behavior of semi-solid slurries forms the backbone of semi-solid processing of metallic alloys. In particular, the effects of several process and metallurgical parameters such as shear rate, shear time, temperature, rest time and size, distribution and morphology of the primary phase on the viscosity of the slurry needs in-depth characterization. In the present work, rheological behaviour of the semisolid aluminium alloy (A356) slurry is investigated by using a high temperature Searle type Rheometer using concentric cylinders. Three different types of experiment are carried out: isothermal test, continuous cooling test and steady state test. Continuous decrease in viscosity is observed with increasing shear rate at a fixed temperature (isothermal test). It is also found that the viscosity increases with decreasing temperature for a particular shear rate due to increasing solid fraction (continuous cooling test). Thixotropic nature of the slurry is confirmed from the hysteresis loops obtained during experimentation. Time dependence of slurry viscosity has been evaluated from the steady state tests. After a longer shearing time under isothermal conditions the starting dendritic structure of the said alloy is transformed into globular grains due to abrasion, agglomeration, welding and ripening.

Rheological Behavior of Semi-Solid Slurry of A356 Alloy at High Shear and Cooling Rates

The rheological behavior of semisolid aluminium alloy (A356) slurry is investigated by using a concentric cylinder viscometer under high cooling rate (30 to 50°C/min) and high shear rate (650 to 1500s-1) conditions. Two different series of experiments are carried out. In all of these experiments, the pellets of A356 alloy are poured into the outer cylinder where they melt completely by resistance heating. When the inner cylinder is placed concentrically, the molten metal resides in the annular space between the cylinders. As the inner cylinder rotates, the alloy is sheared continuously during cooling from a temperature of 630°C, and a slurry forms. In the first series of experiments, for different cooling rates, shearing continues under a constant shear rate until rotation of the inner cylinder stops. During experiments, the temperature of the slurry is measured continuously using a K-type thermocouple, from which the solid fraction is calculated. In the second series of experiments, the molten alloy is cooled and sheared continuously at different shear rates for a given cooling rate. The apparent viscosity of the slurry is calculated by measuring the torque applied to the inner cylinder and its rotational speed. The results show that the slurry viscosity increases with increasing fraction of solid and increasing cooling rate, and it decreases with increasing shear rate. At high values of shear and cooling rates, the viscosity varies gradually up to a solid fraction of about 0.5.