Casting Fluidity Research Articles

Dispersion stability of Y-TZP/Ce-TZP powder system and slip casting

The zeta potential and apparent viscosity measurements of 3Y-TZP, 12Ce-TZP and 3Y-TZP/12Ce-TZP suspensions, has allowed the slip casting conditions for the preparation of multilayer composites have been examined. The influence of heat treatment on the sintered density, microstructure and crystalline phase of multilayer composites was also studied. The isoelectric point of both 3Y-TZP and 12Ce-TZP suspensions was near pH 8 and that of 3Y-TZP/12Ce-TZP was at pH 8.6. The suspensions exhibited pseudoplastic flow, showing a decrease in viscosity with increasing shear stress. A small (0.3 wt%) addition of an organic deflocculant gave 3Y-TZP and 3Y-TZP/12Ce-TZP suspensions with 15 and 20 vol% solid contents an appropriate fluidity for slip casting, but an additional electrolyte was required to reduce viscosity in 12Ce-TZP. Dense (>98% of theoretical) multilayer composites with grain size of 0.3–2.2 μm were obtained after sintering at 1500°C.

Fluidity and microstructure formation during flow of Al- SiC particle composites

This article presents the results of casting and spiral fluidity in a Al-7 wt% Si alloy reinforced with 10,15, and 20 vol% SiC particles in permanent molds. The fluidity of the Al-SiC slurry increases linearly with temperature up to about 760 °C. Above this temperature, the casting fluidity of the Al-SiC particle slurry does not change significantly with an increase in temperature. In several cases, the fluidity decreased at temperatures above 760 °C. The fluidity of Al-SiC melts containing 9-μm SiC particles decreased with an increase in volume percentage of SiC up to 15 vol% (the range studied), presumably due to an increase in the viscosity of the melt with increasing volume percentage of dispersoid and changes in thermophysical properties of the composite. However, the fluidity of Al-20 vol% SiC of 14-μm particle size is higher than the fluidity of Al-15 vol% SiC 9-μm particles, indicating the role of particle size and surface area in de-creasing fluidity. Composite slurries travel farther in a channel of larger cross sections compared to channels of smaller cross sections under similar conditions. Casting fluidity increases linearly with an in-crease in cross section of the channel. A model has been proposed to calculate the values of fluidity of the composite as a function of particle volume percent, superheat, flow velocity of the melt, and the cross sec-tion of the flow channel. Experimental observations have been compared with the predictions of the model, and some deviations have been attributed to settling and segregation of SiC particles observed through microstructural examination.

The solidification microstructure of particulate reinforced aluminium/SiC composites

This paper considers the factors influencing the production and microstructure of cast AlSiC composites. The stability of SiC in molten aluminium alloys is particularly important, and it is shown the AlSi casting alloys have low reactivity with SiC. As a result, the commercial casting alloys can be remelted and cast to shape, provided melt temperature and holding time is controlled, and account is taken of the settling of SiC due to density effects. The low silicon-content wrought alloys, however, cannot be straightforwardly remelted owing to the rapid formation of Al 4C 3, which also affects the casting fluidity of the composite. During solidification the SiC particles are rejected ahead of the meniscus to be eventually trapped in the interdendritic regions. This results in the distribution of SiC being dependent on the solidification rate of the billet.

Effect of experimental variables on casting fluidity and fluid life of liquid tin

The extent and duration of flow (casting fluidity and fluid life) of liquid tin along tubular Pyrex moulds has been measured as a function of melt superheat, mould bore, and mould material for injection under reduced pressure, gravity, and positive pressure, both with and without prior stirring of the injected melt. Macrostructural examination of the resulting fluidity samples showed that cessation of flow was triggered by sufficient inward penetration of columnar growth (vein-closure mechanism) at some distance from the mould entrance except when stirring of the melt had been carried out at low superheat before injection. In that case, growth was fully equiaxed and within the flowing stream so that cessation of flow was then expected to be governed by sufficient solidification at the advancing tip of the flowing stream. Comparison of measured fluid life with predictions of time to complete freezing in a cylindrical mould suggests that freezing occurred under heat-transfer conditions intermediate between Newtonian and ideal.MST/79

Effect of experimental variables on casting fluidity and fluid life of liquid tin

Effect of experimental variables on casting fluidity and fluid life of liquid tin

Fluidity of mica particle dispersed aluminium alloy

Cast aluminium alloy-mica particle composites were made by dispersing mica particles in a vortex produced by stirring the liquid Al-4 wt% Cu-1.5 wt% Mg alloy and then casting the melt containing the suspended particles into permanent moulds. Spiral fluidity and casting fluidity of the alloy containing mica particles in suspension were determined. Both the spiral fluidity and the casting fluidity of the base alloy were found to decrease with an increase in volume or weight percent of mica particles (of a given size), and with a decrease in particle size (for a given amount of particles). The fluidities of Al-4 wt% Cu-1.5 wt% Mg alloys containing suspended mica particles were found to correlate very well with the surface area of suspended mica particles. The regression equation for spiral fluidity Y (cm) as a function of surface area of mica particles per gram of spiral X (cm2 g−1) at 700° C was found to be Y=42.62−0.42X with a correlation coefficient of 0.9634. The regression equations for casting fluidity Y′ (cm) as a functiono of surface area of mica particles per gram of fluidity test piece X′ (cm2 g−1) at 710 and 670° C were found to be Y′=19.71−0.17X′ and Y′=13.52−0.105X′ with correlation coefficients of 0.9194 and 0.9612 respectively. The percentage decrease in casting fluidity of composite melts containing up to 2.5 wt% mica with a drop in temperature is quite similar to the corresponding decrease in the casting fluidity of base alloy melts (without mica). The change in fluidity due to mica dispersions has been discussed in terms of changes in viscosity of the composite melts. However, the fluidities of these composite alloys containing up to 2.5 wt% mica are adequate for making a variety of simple castings including bearings for which these alloys have been developed.

Melting, degassing, and casting characteristics of Al-11·8Si alloys containing dispersion of copper-coated graphite particles

The effects of additions of copper-coated graphite particles on the spiral fluidity, casting fluidity, and hot-tearing characteristics of Al-11·8Si alloys were studied. The remelting and degassing characteristics of aluminium-graphite-particle composites made from copper-coated graphite particles are also reported. Spiral fluidity and casting fluidity of Al-11·8Si alloys decreases with an increase in the amount of suspended graphite particles of a given size and shape, and a decrease in the particle size or sphericity for a given vol.-%. Regression equations relating spiral and casting fluidity to surface area of suspended graphite particles have been derived. The decrease in spiral and casting fluidity of Al-11·8Si alloys owing to additions of copper-coated graphite particles is attributed to an increase in the effective viscosity of the melt. Additions of up to 4 wt-% of copper-coated graphite particles do not increase significantly the hot-tearing tendency of Al-11·8Si alloys. Degassing of Al-11·8Si-graphite composite melts by hexachloroethane leads to the rejection of graphite particles. However, these melts can be degassed readily with nitrogen.

Casting fluidity of binary alloys of lead with arsenic, silver, and bismuth

The casting fluidity of alloys of lead with arsenic, silver, and bismuth has been determined by the vacuum fluidity method. In some tests the cooling rate was varied by heating the glass tube moulds. The maximum fluidity was found to occur at compositions higher in alloying element than the equilibrium eutectic composition. An explanation is attempted in terms of non-equilibrium cooling behaviour.