Coupled heat and fluid flow model and experimental verification of aluminium plate die casting

Abstract

The present work aims to forecast mould filling, void shape, location and size as well as columnar to equiaxed transition (CET) in commercial pure aluminium casting. A model coupling the momentum equations of the fluid flow and heat transfer equations is presented, in which metallostatic pressure, air gap and oxide layer are considered. Different casting parameters were investigated such as casting configuration by varying the plate thickness from 5 to 20 mm, melt superheat from 40 to 120°C, mould preheat up to 200°C and different pouring heads ranging from 0·3 to 0·6 m. Regarding the microstructure and void formation, the approach based on the Niyama criterion, was considered. The experimental verification of the model was achieved by gravity die casting in the form of a rectangular cavity. Voids inside aluminium plate were investigated by X-ray imaging. Microstructure and CET was investigated microscopically. The supposed model proves its validity for mould filling and in detecting the void features and CET.     

Effect of metal purity and testing procedure on surface tension measurements of liquid tin

The surface tension of liquid tin of three different grades of purity (99.85, 99.96, and 99.999%) was measured by the classical sessile drop method over the temperature range 523–1023 K, in heating and cooling regimes. The results obtained show that the metal purity affects the values of surface tension and its temperature dependence. The highest values of surface tension and smooth linear temperature dependence were obtained in cooling regime for tin of the highest purity. With increasing content of impurities, both surface tension and its temperature coefficient decrease while the scatter of the data increases. The surface tension values measured on heating regime show higher scatter, compared to those obtained in cooling regime, and the temperature dependence of the surface tension is curvilinear rather than linear.     

Effect of the casting process variables on microporosity and mechanical properties in an investment cast aluminium alloy

The casting process variables considered were the shell mould preheat temperature, the pouring temperature and the melt hydrogen content. The paper reports progress on a programme to appraise and optimise the mechanical properties of selected investment castings. The influence of shell preheat temperature, pouring temperature and melt hydrogen content on microporosity and mechanical properties were studied in this paper. Shell preheat temperature and melt hydrogen content are the most important process parameters determining the amount of porosity. All three parameters affect the mechanical properties to varying degrees.     

Effect of the casting process variables on microporosity and mechanical properties in an investment cast aluminium alloy

The casting process variables considered were the shell mould preheat temperature, the pouring temperature and the melt hydrogen content. The paper reports progress on a programme to appraise and optimise the mechanical properties of selected investment castings. The influence of shell preheat temperature, pouring temperature and melt hydrogen content on microporosity and mechanical properties were studied in this paper. Shell preheat temperature and melt hydrogen content are the most important process parameters determining the amount of porosity. All three parameters affect the mechanical properties to varying degrees.     

Effect of experimental variables on the inertization of galvanic sludges in clay-based ceramics

The incorporation of several industrial wastes in ceramic matrixes had been attempted as an effective low expense technique for the fixation of metallic species in usable products or simply to reduce the residue volume for further disposal. However, the dominant mechanism of the inertization process and the relevant influent parameters are still unknown, mostly due to the complexity of the systems. This work reports the effect of several processing parameters such as the mixing time, the calcination temperature and duration, the relative amount of sludge, and the physical aspect of the sample (powdered or pressed pellets) on the fixing level of relevant species (SiO2), SO4(2)-, Zn, Ni, Ca, Cu, Cr) by leaching in different media (aqueous, acetate, and citrate). Statistical tools were used to define the relevance of each experimental variable on the inertization process of the used galvanic sludge. The relative amount of sludge in the mixture, the calcination temperature and the agglomeration state of the sample were found to be the most influent parameters of the inertization process. The incipient reaction between sludge and ceramic matrix components points out for the dominance of a macro-encapsulation mechanism.     

Experiments on interaction of liquid tin with solid copper

Abstract

The reaction of liquid tin with solid copper has been studied by heating small volumes ofpure tin on copper coupons at various temperatures and times, and evaluating the resulting reaction metallographically. Three reaction temperatures were used:260,400,and450 ° C. Specimen geometry was chosento simulate a typical solder joint. The reaction was observed to occur in two stages: an initial fast stage with copper/liquid tin interface movement rates from 0.2 μm s^-1 at260 ° C to 0.8 μm s^-1 at 450 ° C, followed by a much slower stage. It was concluded that the first stage corresponds to direct dissolution of copper in liquid tin up to or beyond the liquidus concentration for the reaction temperature used.This is followed by the formation of an intermetallic compound layer atthe copper/liquid interface. Subsequent copper dissolution then occurs by solid state diffusion through the compound layer, a much slower process than direct dissolution.     

Analysis of fluid flow in centrifugal casting

Centrifugal casting process is a fast process with melt, cast and moulds being opaque. It is almost impossible to observe the melt behavior during casting. Cold modeling experiments were conducted using horizontal transparent moulds and transparent fluids of different viscosities to study the effect of different process variables on the flow pattern. Effects of the thickness of fluid cylinder, viscosity of the fluid, diameter of the mould, and rotational speed of the mould on the formation of complete hollow fluid cylinder are investigated. The influence of rotational speed has been studied in aluminum casting. The cylinders are cast at different rotational speed with varying thickness. It is observed that the speed required to form uniform cylinder increases with the increase in thickness of a fluid cylinder. As rotational speed is increased the hardness of the cast cylinder also increases. The flow patterns seen in cold modeling experiments and actual castings agree reasonably well.     

Effects of Sn addition on as-cast microstructure, mechanical properties and casting fluidity of ZA84 magnesium alloy

The effects of Sn addition on the as-cast microstructure, mechanical properties and casting fluidity of the ZA84 magnesium alloy are investigated. The results indicate that adding 0.5–2.0 wt.%Sn to the ZA84 alloy not only can result in the formation of Mg₂Sn phase but also can refine the Mg₃₂(Al, Zn)₄₉ phase and suppress the formation of Mg₃₂(Al, Zn)₄₉ phase, and with the increase of Sn amount from 0.5 wt.% to 2.0 wt.%, the morphology of Mg₃₂(Al, Zn)₄₉ phase gradually changes from coarse continuous and/or quasi-continuous net to relatively fine quasi-continuous and/or disconnected shapes. In addition, adding 0.5–2.0 wt.%Sn to the ZA84 alloy can improve the tensile and creep properties, and casting fluidity of the alloy. Among the Sn-containing ZA84 alloys, the ZA84 alloy added 1.0 wt.%Sn exhibits the best ultimate tensile strength, elongation and casting fluidity while the ZA84 alloy added 2.0 wt.%Sn has the best yield strength and creep properties.     

Diffusivity and thermal conductivity in solid and liquid tin

A method for determination of diffusivity of liquid metals in a hemispherical volume is described and experimental results are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 3, pp. 490–494, September, 1973.     

Temperature dependence of the density of liquid tin

The two-capillary pycnometer method is used to study the temperature dependence of the density of tin in the temperature range fromT _melt to 770 K. The measurements are carried out in a superhigh vacuum in higher purity samples. The experimental data are described by an equation of the straight line p(T) = 7374.7 -676.5 x 10_-3Trand do not confirm the anomaly (observed previously by some authors) in the form of a minimum on the poly therm of the density of tin in the temperature range from 610 to 700 K     

Solidification and microstructure characterizations of eutectic aluminum-silicon casting alloy with the addition of tin

The effects of tin (Sn) addition on aluminum-silicon and α-aluminum phase solidification parameters as well as eutectic aluminum-silicon casting alloy microstructure are systematically investigated. In this research, these characteristic parameters are examined by using computer-aided cooling curve thermal analyses. The results of microstructure analyses and cooling curves show that tin alters silicon structure. By increasing the amount of tin up to 1 wt.%, α-aluminum phase nucleation temperature, aluminum-silicon phase growth temperature, and last phase solidus temperature increase. The mean area of silicon particles decreases when 0.1 wt.% tin is added but by its further increasing up to 1 wt.%, silicon particle mean area increases. It means that increase of tin content does not lead to silicon structure modification in this type of aluminum-silicon alloy. Besides, by increasing the amount of tin, the reaction temperature of the last phase is increased by the formation of intermetallic compounds such as ternary compounds (Al−Si−Sn).     

Influence of oxygen contamination on the surface tension of liquid tin

The surface tension of liquid tin has been measured by the sessile-drop technique as a function of temperature, in the range 232 T (°C) 800 and under different atmospheres. It is shown that oxygen strongly affects the surface tension values and that, under nominally very clean conditions, a considerable scatter of experimental results occurs. This scatter can be explained by taking into account kinetic factors, especially those related to the gaseous fluxes around the molten drop. By this procedure, a number of experimental results can be singled out, which corresponds to clean surface conditions. On the basis of these results, the following expression for surface tension politherm is proposed: (mN m^–1 = 581-0.13) (t-232).     

Diffusion of tin in lead tin telluride epitaxial layers grown by liquid phase epitaxy

The distribution of tin in epitaxial layers of lead tin telluride grown by liquid phase epitaxy on lead telluride substrates has been determined by electron probe microanalysis. The diffusion coefficients calculated from the experimental data agree approximately with the literature values.     

高分子液晶电流变流体的研究

研究以聚硅氧烷侧链高分子液晶作为分散相 ,制备均相的电流变流体 (ER流体 ) ,测试其在电场下表观粘度、剪切应力等流变学性质的变化。结果发现 :以硅油作分散介质 ,含6 6 7%的高分子液晶的流体 ,在剪切速率为 30 0s- 1时 ,电场强度 (E)从 0升至 2kV/mm ,流体的剪切应力从 2 0 0Pa·s上升至 540 0Pa·s ,表观粘度由 2 0 0 0mPa·s上升至 10 0 0 0mPa·s ,并且 ,流体在80℃时仍有很强的电流变效应 ,能在较宽的温度范围内使用     

Influence of liquid metal feeding on the flow and macrosegregation in DC casting

ABSTRACT

The influence of liquid metal feeding on the flow and macrosegregation during direct chill (DC) casting of Al-4.5wt-%Cu billets is investigated. An analytical study for constricted inlets predicts that the inflow only reaches the bottom of the sump for narrow inlets, a result confirmed by steady-state axisymmetric simulations of equiaxed solidification. For wide inlets, and inlets using a combo bag, the inflow is swiftly entrained towards the chill and the final macrosegregation predictions are all similar. For narrow inlets without a combo bag, penetration of the thermal jet to the bottom of the sump locally delays solidification producing an inclination in the packed solid interface and the possible growth of columnar dendrites in this region.     

Studies of casting and LB films of ferroelectric liquid crystalline polysiloxane

Monolayers of side chain ferroelectric liquid crystalline polysiloxane have been successively transferred onto appropriate substrates by vertical dipping method to study the morphology and the orientation of the mesogens and the side chains by UV spectra and polarized FT-IR spectra and X-ray diffraction. The spectra for casting film and LB film are compared. The molecules in LB films are found to be more orientated along the normal of the substrate at an angle of 37° for the mesogens as the side chain as found by polarized FT-IR spectra and transmitting FT-IR spectra than casting film. Layer structure is also confirmed by X-ray diffraction results. The mesogens are found to form H-aggregates structure in bulk phase and LB films from UV spectra. Temperature-dependent UV spectra have revealed the change of the tilt angle of the mesogens inside the layer of both bulk phase and LB films.     

Fatigue life assessment of aluminum alloys with casting defects

The fatigue lifetimes of cylindrical aluminum specimens containing shrinkage cavities were measured. The results were compared with those of specimens without macroscopic cavities (DC cast). Two different heat treatments were considered: T4 (naturally aged) and T6 (near peak aged). The pore shape and distribution in the specimens were complex. Pores with a maximum diameter larger than 0.2 mm resulted in a significant reduction of the lifetime. Numerical calculations were carried out to predict the fatigue life and crack growth model taking crack closure effects into account was used. This model tended to give somewhat nonconservative results when compared with test results. Modification of the model, taking a short crack effect into account, gave conservative results.