Pouring Temperature Research Articles

On the Solidification and Feeding of a Ductile Iron Casting

ABSTRACTSolidification of a simple casting made of ductile iron is mathematically modeled in this work. The model is able to numerically simulate the cooling rate and solidification of the whole casting system composed by a cubic piece, a blind riser connected through a rectangular neck, and immersed in a green sand mold. The center of the neck acts as a valve that allows the flow of liquid metal between the casting and the riser based on the feeding technique known as Pressure Control Risering (PCR). The developed model couples the energy conservation equation and the solidification kinetics of ductile iron, through the statement of proper nucleation and growth laws. This model is satisfactorily validated by comparing the thermal histories predictions with experimental cooling curves obtained in the foundry laboratory for the same casting. According to a process analysis developed in this work, the pouring temperature is the variable that affects the most the solidification and the feeding behavior, since it increases significantly the solidification times in all regions of the casting system.

Modelling of solidification microstructure evolution of twin-roll casting magnesium strip using cellular automaton

Cellular automaton （CA） is applied to simulating the microstructure evolution during the solidification， and finite element method （FEM） was used for solving the conservation equations which govern the macro-transport phenomena during the twin-roll casting process of the magnesium strip in the molten pool. Coupling CA with FEM can predict the microstructure evolution during solidification involving nucleation and growth of the grains. On the basis of this CA-FEM method，the effects of the main parameters involving pouring temperature， casting speed and pool height on the characteristic of solidification microstructure such as grain size and orientation can be quantitatively clarified by numerical simulation， which can provide the theoretical basis for the optimization of the processing parameters and the control of the solidification structure.

In situ silicon particle reinforced ZA27 composites: Part 1 – Microstructures and tensile properties

In situ silicon particle reinforced ZA27 composites were fabricated by liquid metallurgy route. The solidification process was specially discussed. The effects of pouring temperature, silicon content and phosphorous modification on microstructures and tensile properties of the composites were investigated. The results indicated that the solidification process included three stages, primary silicon particle crystallisation (the primary phase was α-Al dendrites when silicon content was lower than 1·5 mass%), binary Al–Si eutectic reaction and quaternary Zn–Al–Si–Cu eutectic reaction. The addition of silicon into the ZA27 alloy changed the α dendrites from the original equiaxed shape to a two-dimension (2D) column dendrites and this change was further enhanced with the increase in silicon content. Phosphorous did not only fine the primary silicon particles, but also fined the α dendrites. The sizes of both the silicon particles and α dendrites decreased and the particles distributed more uniformly as the pouring temperature increased. However, the particle size increased and their distribution became more agglomerated as the silicon content increased. The tensile properties increased with increasing pouring temperature while those decreased as the silicon content increased. There were four factors that led the composites to fracture during tensile testing, porosities, fracture of the silicon particles, debonding of the interfaces of silicon particles/matrix and debonding of the interfaces between the 2D column dendrites. The contribution of each mechanism to the fracture varied with the pouring temperature or silicon content.

Microstructural Evolution of ETIAL 160 Aluminium Alloy Feedstock Produced by Cooling Slope Casting

Owing to its superior flow and mould-filling capability, a fully globular structure is essential for semisolid processing technologies. The present work was undertaken to identify the cooling slope casting process parameters that, upon heating to the semisolid state, gives the required globular structure for the ETIAL 160 alloy. Of the two pouring temperatures investigated, 605 °C and 615 °C, the lower pouring temperature was found to provide more globular grains surrounded by liquid phases.

Forging Process of Wrought Aluminum Alloy with Controlled Solid Fraction by Electromagnetic Stirring

This study demonstrates the indirect rheoforging of wrought aluminum alloys fabricated by electromagnetic stirring (EMS). EMS was carried out by varying pouring temperature of theological material and subsequently the rheo-material was forged into the sample which consisted of the direct and indirect forging part, by varying the applied forging pressure. The rheo-material completely filled the die cavity at the applied forging pressure of 150 MPa. To transfer the densification pressure to the end of the part, the applied forging pressure of over 170 MPa was necessary. To control liquid segregation, solid and liquid phases distribute uniformly by deriving the laminar flow. When liquid segregation occurred significantly during rheoforging, the strength revealed as low as 268 MPa. Investigating relationship between microstructural features and mechanical properties of the product, the rheoforged material through EMS revealed the fine and globular microstructure. Microstructure with uniform distribution of solid and liquid phase (no segregation) showed good mechanical property of the rheoforged material whose tensile strength was 341 MPa for Al6061.

Vertical Centrifugal Casting of Aluminum Matrix Particle Reinforced Composites

Centrifugal casting of composites gives rise to a certain distribution of reinforcement particles due to the natural liquid flow and solidification pattern. The particle rich regions are strongly influenced by rotational speed of the mold, particle size, relative density difference between particles and melt, initial pouring temperature, initial mold temperature, and by the nature of the particles added [1—3]. In the present work zirconia, silicon carbide, and ilmenite particles have been added to an aluminum—magnesium alloy and cast using a vertical centrifugal casting machine. The particle distribution and the resultant hardness variation have been analyzed. The particles are invariably associated with porosity. In the case of ilmenite particles, there is extensive reaction with the liquid metal. The combined effect of vol % of particles, porosity, and extent of reaction gives rise to a complex hardness variation. There is a substantial increase in hardness with particle addition. The particles tend to concentrate at the middle of the casting.

Characterization of the refractory coating material used in vacuum assisted evaporative pattern casting process

In the production of the casting using evaporative pattern of expandable polystyrene, the refractory coating applied to the pattern is an extremely critical factor. The coating is not required merely to prevent a direct contact with the sand and metal. But its main task is to support the sand during the brief interval between the gasification and replacement of pattern by the molten metal. In the present study, refractory filler material (flyash) has been used for coating the evaporative polystyrene patterns. Effect of temperature on the powder mixture containing zircon flour, filler material and binder was determined using Differentially Thermal Analysis (DTA) in the range from ambient temperature (20 °C) to 1000 °C. Powder particle morphology was analyzed by the scanning electronic microscope. X-ray diffraction analysis of the coating samples was carried out for 2 θ values from 10° to 80°. Prepared slurry was applied on the polystyrene pattern of 20 kg/m 3 density. Coating thickness was maintained between 0.15 and 0.20 mm. Al–7% Si alloy was poured at the pouring temperature (700 °C). Microstructure of the casting was investigated. The result reveals that the sample 4 has less material loss. It contains large and small particles and fine pores. Particles of different grain size contribute to better uniform, continuous coating on pattern due to cohesion between the particles. The phases (ZrSiO 4, TiO 2, Fe 2O 3, Al 2O 3 and SiO 2) make the stable compound which leads to high temperature refractoriness.

Effect of local chilling on morphology of primary α(Al) in semi-solid A356 alloy

The semi-solid slurry of A356 alloy was prepared by low superheat pouring and slightly electromagnetic stirring, in which a pure copper rod was used to produce local chilling. The effect of chilling by the rod on morphology and size of primary α(Al) in A356 was researched. The results indicate that the chilling by the rod remarkably affects the morphology and the size of primary α(Al). Primary α(Al) with particle-like shape is distributed uniformly in A356, and there is no transient area in structure morphology. Compared with the samples prepared without the local chilling, the nucleation rate, morphology and grain size of primary α(Al) in A356 prepared by low superheat pouring and slightly electromagnetic stirring with the rod are markedly improved. Under the condition of chilling, the pouring temperature can be suitably raised to obtain primary α(Al) with particle-like shape.

Preparation of semi-solid AlSi7Mg alloy slurry

In this article, semi-solid AlSi7Mg alloy slurry was prepared by low superheat pouring and weak electromagnetic stirring. The effects of pouring temperature and stirring power on the microstructure of the AlSi7Mg alloy slurry were studied. The results showed that the semi-solid AlSi7Mg alloy slurry, 127 mm in diameter, could be prepared by using the low superheat pouring and weak electromagnetic stirring technology and this new technology could save energy and make the pouring process convenient. When the liquid AlSi7Mg alloy was poured at 650°C or 630°C, the solidified microstructure of the AlSi7Mg alloy slurry, prepared by weak electromagnetic stirring, was remarkably improved when compared with that of the slurry prepared without stirring. The primary α-Al grains appeared rosette-like or spherical. When the pouring temperature was decreased, the shape of the primary α-Al grains gradually changed from dendritic-like grains to spherical grains. When the pouring temperature was appropriately increased, that is, raised to a certain superheat, the pouring process became easier and an ideal spherical microstructure of the AlSi7Mg alloy slurry, prepared by weak electromagnetic stirring, could also be obtained. In this experiment, when the stirring power was 0.36 kW, the optimized pouring temperature parameter was 630°C. When the AlSi7Mg alloy slurry was prepared by low superheat pouring and weak electromagnetic stirring, the pouring temperature was 630°C. Increasing the stirring power appropriately could gain better spherical primary α-Al grains, but if the stirring power was increased to a certain value, the shape of the primary α-Al grains did not improve further. In this experiment, the optimized stirring power parameter was 0.36 kW.

Effect of grain refining on primary α phase in semi-solid A356 alloy prepared by low superheat pouring and slight electromagnetic stirring

The semi-solid slurry of A356 alloy, which is grain-refined by Al-Ti-B master alloy, is prepared by low superheat pouring and slight electromagnetic stirring. The effects of grain refining on the morphology and the grain size of the primary α phase in the slurry manufactured are researched. The results indicate that the slurry with particle-like and rosette-like primary α phases can be prepared by low superheat pouring and slight electromagnetic stirring from liquid A356 alloy grain-refined, in which the pouring temperature can be suitably raised. Compared with the A356 samples without grain refining, the grain size and particle morphology of primary α phase as well as the distribution of the grain with particle-like or rosette-like along radial in the ingot in A356 are markedly improved by grain refining. KEY WORDS Semi-solid; Grain-refined; Low superheat pouring; Slight electromagnetic stirring; A356 alloy; Al-Ti-B

Influence of process parameters on microstructure of semisolid A356 alloy slug cast through vertical pipe

Suitable microstructures required for semisolid casting were formed by using a vertical pipe. Different lengths of vertical pipe, slug dimensions and pouring time were used to investigate their influence on the microstructure of A356 alloy. The results indicate that at the same length of the vertical pipe, the morphology of the primary α(Al) gradually deteriorates by the enlargement in the slug size, but the deteriorating speed slows down with increasing pipe length. They also reveal that the increase in the pipe length improves the microstructure, whereas no further improvement appears when the pipe length reaches a certain value. The optimum length of the pipe obtained in the present work is 430 mm. The microstructure of larger slug poured at higher pouring temperature gets worse and it can be improved by moderately elongating pouring time. The relative mechanisms were also discussed.

Influence of Mold and Pouring Temperatures on Hot Tearing Susceptibility of AZ91D Magnesium Alloy

This research focused primarily on studying the effect of mold temperature on the hot tearing susceptibility of permanent mold cast (PMC) AZ91D magnesium alloy. The results suggest that increasing the mold temperature from 140 °C (282 F) to 380 °C (716 F) had a significant impact on the severity of hot tearing in the alloy. Mold temperatures above 340 °C (644 F) were seen to virtually eliminate hot tears through a morphological change of the alloy’s β-phase regions, which enabled liquid metal feeding of the casting at later stages of solidification and high fractions of solid. Variation of the mold temperature also affected the alloy yield strength and casting porosity. The effect of increasing the pouring temperature in the 680–720 °C (1256–1328 F) range to reduce hot tearing was less pronounced than that of varying the mold temperature.

Effect of solid fraction on the mechanical properties of thixomolded magnesium alloys

The higher the fraction of solid phase in the partly solidified melt during pouring, the poorer the mechanical properties of thixocast components. The solid fraction decreases as the pouring temperature rises. Recommended temperature profiles for the pouring cylinder are shown. The flow characteristics of the partly solidified melt hardly changes as the content of solid matter increases.

Pressure measurement and some observation in lost foam casting

Experiments are being conduced in a photography technique to examine flow of aluminum, cast iron and steel into the molds. The purpose is to observe some parameters such as gas gap length, foam decomposition products, metal front and mold filling time in lost foam casting of aluminum, cast iron and steel. Foam-metal interface reactions and gas evolution have been observed during mold filling. The results indicate that the metal pouring temperature and foam density and coating layer thickness affect mold filling time. In the steel lost foam casting, the gas gap length and gaseous products volume and the mold filling time are significantly larger than the cast iron. In both the cast iron and the steel lost foam casting, the foam pattern escapes from the mold mainly in the form of gases but in the aluminum lost foam casting foam pattern mainly decomposes into liquid polystyrene and no gas gap layer has been observed. Results of back pressure measurements show that with increasing foam density and melt head (sprue height) gas pressure increased significantly.

Fluidity of aluminium die castings alloy

The aim of the present work was to investigate the fluidity of four different high pressure die cast Al–Si alloys at different pouring temperatures. A vacuum fluidity test apparatus was employed to measure fluidity. The analysed alloys showed different flow sensitivities to casting temperatures. Furthermore, it is showed that among the considered alloying elements, magnesium and silicon affected the fluidity of the melt. One alloy was then contaminated with 50% scrap addition, increasing the amount of oxide inclusions. The fluidity of the contaminated melt has then been measured and compared with the fluidity of the clean melt. The results show that the fluidity of the alloy with scrap addition is lower than that of the clean melt. Further the fluidity linearly increases at increasing temperatures within the range between 580 and 680°C until it reaches a plateau at the highest pouring temperatures.

Optimization of tensile properties of evaporative pattern casting process through Taguchi's method

Evaporative pattern casting (EPC) process allows the production of complex parts and reduces machining of the part. To make a casting by EPC process, an expandable polystyrene pattern of the final part is made. In EPC process, all the limitations imposed by the binders and additives are absent as it is a binderless process. In this paper an attempt has been made to achieve a set of values of EPC process parameters that may yield optimum tensile properties to the Al–7% Si alloy castings. The effect of selected process parameters on the tensile properties of Al–7% Si alloy casting and subsequent optimal settings of the parameters have been obtained using Taguchi parametric design approach. The results indicate that the grain fineness number and the pouring temperature are the significant parameters in deciding the tensile strength and percent elongation after fracture of Al–7% Si alloy castings. Time of vibration and degree of vacuum are insignificant parameters. The predicted optimal value of tensile strength and percent elongation after fracture of Al–7% Si alloy castings produced by EPC process are 141.17 N/mm 2 and 2.713%, respectively, at 22 kg/m 3 density of expandable polystyrene pattern.

Numerical Study of Functionally Graded Materials

One-dimensional comprehensive mathematical model coupling particle movement and thermal conduction in the casting mould system is developed. A formula for pressure in liquid metal during the centrifuge process is derived. The model takes into consideration the propagation of solidification front and movement of particles due to centrifugal acceleration which takes place either in the same or in opposite direction to that of the solidification front depending on the relative density difference between the particles and melts. In the force balance expression, repulsive force term is incorporated for the particles that are at the vicinity of the solid/liquid interface to calculate the particle segregation pattern in the casting region The effects of various process parameters such as, rotational speed of the mold, size of the reinforcing material, relative density difference between the particle and melt, initial pouring temperature of the liquid melt, mold pre-heating temperature, heat transfer coefficient between the casting/mold interface are studied. It is noted that for a given set of operating conditions, the thickness of the particle rich region in the composite decreases with increase in rotational speed, particle size, relative density difference between the particle and melt, initial pouring temperature and initial mold temperature. With decrease in the heat transfer coefficient between the casting/mold interface, the solidification time increases which, in turn, results in more intense segregation of solid particulates. Again, with increase in the initial volume fraction of the solid particulates, both the solidification time as well as the final thickness of the particulate rich region increase.

Thixoforming of non-dendritic AA6061 feedstock produced by low superheat casting with and without a cooling slope

Abstract Low superheat casting with and without a cooling slope was employed to produce AA6061 thixoforming feedstock. The dendritic features were more frequent in the latter, suggesting that the degeneration of the dendritic structure was promoted by the cooling slope casting process. Minor differences in the primary phase morphology in the as-cast state were no longer evident after partial melting, with nearly equiaxed polygonal grains in all ingots cast with and without a cooling slope. 5 min soaking at 640 °C was identified as the best reheating practice as it provided the smallest grains and the most complete grain boundary wetting. The slugs machined from AA6061 ingots cast from a pouring temperature of 680 °C with and without a cooling slope were both successfully thixoformed into sound parts with no signs of porosity and segregation. The T6 heat treatment produced hardness values as high as 107 HB which compare very favourably with those of the extruded products and are even better than that obtained in the thermomechanically processed feedstock.

Undesirable Graphite Morphologies Incidence in Inoculated Grey Irons

Successful inoculation is not guaranteed and effects may even be deleterious. The main risks are the appearance of types B and D graphite, associated with ferrite and/or carbides due to lack of control of undercooling during eutectic solidification. Alternatively coarse type C graphite in hypo to eutectic grey irons may result from inadequate or excessive inoculation. Sulphur and aluminium content in a molten iron are considered to be the main factors to control the degree of eutectic undercooling, graphite morphology and inoculation efficiency. Thermal conditions, such as superheating, inoculation and pouring temperature play an important role in controlling these effects. Cooling rates due to different mould materials and casting thickness were also considered. In order to resolve individual problems, different inoculant systems have to be considered, such as Sr-FeSi, Ca-FeSi, Ti,Ca-FeSi, Zr,Ca-FeSi, Ba,Ca-FeSi, RE-FeSi (Ca). The present paper made a synthesis of other published papers by the authors, but also added many original un-published results.

Influence of Interfacial Reaction on the Fluidity of A356 Al-SiC p Composites—A Theoretical Approach

Fluidity behavior of the A356 Al alloy and A356 Al–SiCp composites has been theoretically predicted using the Flemings model after incorporating (1) the solidification behavior of the alloy; (2) the decrease in flow velocity due to surface tension and friction losses; and (3) the increase in viscosity of composite slurries due to size, shape, and volume fraction of the reinforcement. It is observed that the fluidity values of A356 Al alloy and A356 Al–10 vol pct SiCp composite predicted by the modified Flemings model are in good agreement with the experimental values reported in the literature. On the other hand, the theoretically calculated fluidity length of A356 Al–15 and 20 vol pct SiCp composites using the modified Flemings model agrees well with the experimental results only up to 750 °C and 710 °C, respectively. However, above these respective temperatures, the experimental spiral length decreases with pouring temperature, whereas the theoretically calculated spiral length increases linearly as a function of pouring temperature. Incorporation of experimentally calculated interfacial reaction terms in the modified Fleming model makes the predicted and experimental values of fluidity of A356 Al–15 and 20 vol pct SiCp composites closer in the entire temperature range. Thus, the high dependence of the fluidity of A356 Al–SiCp composites on the morphology of the interfacial reaction product is demonstrated.