Pouring Temperature Research Articles

Relationships between cooling rate, copper content and mechanical properties of monotectoid based Zn–Al–Cu alloys

One binary Zn–40Al and four ternary Zn–40Al–(1, 2, 3, 4) Cu alloys were produced by permanent mould casting at different pouring and mould temperatures. Cooling curves were obtained, and the average cooling rate for each alloy ingot was determined. The hardness, tensile strength, percentage elongation and impact energy of the alloys were measured after studying their microstructure by optical and electron microscopy. The effects of cooling rate and copper content on the structure and mechanical properties of the alloys were investigated. The hardness, tensile strength, percentage elongation and impact energy of the alloys were found to increase with increasing cooling rate. These properties, except percentage elongation, also increased with the increasing copper content of the alloys, but the impact energy and tensile strength decreased when the copper content exceeded 1% and 2%, respectively. As a result of a mathematical evaluation of the experimental data, the relationships between mechanical properties, cooling rate and copper content of the alloys were determined and are presented using three-dimensional graphs.

The effect of grain refining and oxide inclusion on the fluidity of Al–4.5Cu–0.6Mn and A356 alloys

The effect of grain refinement and oxide inclusion on the fluidity of Al alloy was investigated with a test casting with eight thin flow channels. Pouring in air increased the amount of oxide in the A356 melt. The fluidity compared between normal A356 melt and contaminated melt. The amount of oxide was evaluated qualitatively by ultrasonic treatment. The flow length varied linearly with the pouring temperature. By adding Ti and Al–5Ti–B, fluidity increased. The grain size decreased by adding grain refiner. The fluidity depended on the degree of grain refining. It was noticed that pouring in air increased the amount of oxides in the melt by ultrasonic treatment. The fluidity of contaminated melt was decreased comparing to the normal one especially in lower temperature.

A transient simulation and dynamic spray cooling control model for continuous steel casting

A two-dimensional heat-transfer model for transient simulation and control of a continuous steel slab caster is presented. Slab temperature and solidification are computed by the model as a function of time-varying casting speed, secondary spray cooling water flow rates and temperature, slab thickness, steel chemistry, and pouring and ambient temperatures. Typically, the solidification path, temperature-solid fraction relationship, is prescribed. However, if these data are not available, a microsegregation solidification model that approximates the effects of steel chemistry and cooling rate is incorporated in the caster model. Measured slab surface temperatures recorded from an operating caster are compared with predictions from the transient model. These demonstrate that the model typically can predict the temperature response at the slab surface within 30 °C. Results of several simulations are given to demonstrate the effects of changing casting conditions on the slab thermal profile, end of liquid pool, and solidification end point. A control methodology and algorithm suitable for online control of a continuous casting machine is described, and the ability to control the surface temperature profile by dynamically adjusting secondary spray cooling flow rates is demonstrated by simulation. Results from a preliminary version of the model that is capable of running in real time are presented and are compared with the slower, but more realistic, version of the model.

Evolution of primary phase in solidification of Al-Si alloys

The morphology of primary phase in solidification of hypo-eutectic Al-Si alloys has been investigated by both experiment and numerical simulation using the modified cellular automaton(MCA) method. In order to generate the globular structure without any thermo-mechanical stirring, the effects of pouring temperature, cooling rate and inoculation on the evolution of globular structure were examined. The optimum condition for obtaining uniform and fine globular structure is that the pouring temperature should be as closely low as to the liquidus and the cooling rate should be less than 0.3°C/sec. As the pouring temperature and the cooling rate increase, the primary phase transforms from globular to rosette-like, and finally to dendritic structure. The inoculation with nucleation potency is also very effective in forming a globular structure. The dominant mechanism responsible for the evolution of globular structure was found to be the increase of nucleation sites due to the lower pouring temperature, inoculation, and uniform solute distribution due to the lower cooling rate.

Relationships between secondary dendrite arm spacing and mechanical properties of Zn-40Al-Cu alloys

Three ternary monotectoid-based Zn-40Al-(1, 2, 3%) Cu alloys were produced by permanent mould casting at different pouring and mould temperatures. The average cooling rate for each alloy was determined. Structure of the alloys was examined using optical and electron microscopes and their hardness, tensile strength, percentage elongation and impact energy were measured. As a result of these investigations the relationships between structure and mechanical properties of the alloys were determined.

Effect of cooling rate on structure and mechanical properties of monotectoid zinc-aluminium alloys

The cooling curves of a number of monotectoid zinc-aluminium allows have been obtained during casting at different pouring and mould temperatures using thermocouples and an analogue-digital converter in a computer. The average cooling rate for each ingot of the allows was determined by taking the derivative of the cooling curves. The effect of cooling rate on the structure and properties of the alloys was investigated. It was observed that as the cooling rate increased the secondary dendrite arm spacing of the alloys decreased but their hardness, tensile strength and percentage elongation increased. Correlation of the experimental results showed that the cooling rate of the alloys could be related to their secondary dendrite arm spacing, hardness, tensile strength and percentage elongation using first and second degree mathematical equations. In addition, the Skenazi equation was found to be applicable to these alloys. As a result of this work, the optimum range of cooling rate for the alloys was found to be between 4·40−4·56 K s-1.

Effect of reducing conditions on sludge melting process

The objective of this study was to compare the effects of CO/CO 2 reducing conditions with those of air oxidizing conditions on the pouring temperature of the sludge melting process and the heavy metal leachability of the resultant sludge slag. Synthetic sludge ash composed of SiO 2, CaO and Al 2O 3, as well as sewage sludge ash generated from a laboratory incinerator was employed. The experimental results indicated that the pouring temperatures are significantly reduced under the reducing conditions of CO/CO 2, or 24 and 77 °C lower than under air conditions for synthetic and sludge ash, respectively. The heavy metal leaching tests further indicate lower heavy metal concentrations present in the leachate under the reducing conditions, notably an order of magnitude lower in Zn. However, X-ray diffractogram indicates similar peaks for these two slags produced under different conditions.

Experimental and computational study of nozzle electromagnetic stirring and its effects on solidification structure

Centreline shrinkage and segregation in continuously cast billets have an adverse effect on cast product quality. Nozzle electromagnetic stirring (N-EMS) is an effective method to refine the solidification structure of continuously cast billets and thereby improve the cast product quality. The effect of N-EMS on the solidification structure of continuously cast Sn-3·5Pb alloy has been investigated by means of experiments and numerical analysis. The results show that, upon imposing N-EMS, crystal grains within the billets are refined and continuous casting can be conducted at a lower pouring temperature; the solidification structure of the resulting obtained billets is much finer than without N-EMS. The mechanism by which the solidification structure of the billets is improved is considered to be a change in the flow and temperature distribution of molten metal in the nozzle.

Study on the semi-solid rheocasting of magnesium alloy by mechanical stirring

In this work, the effect of the pouring temperature of magnesium melt, the preheating temperature of the barrel of the screw mixer and the shear rate, on the solidified microstructures of semi-solid slurry was investigated by the mechanical stirring method. The appropriate processing parameters of slurry preparation were obtained. The mold filling for a thin-walled casting was examined. The results indicated that the solid volume fraction of non-dendritic structure increased with decrease in the pouring temperature of the magnesium melt and in the barrel preheating temperature of the screw mixer. Also, the grain size of the primary α-phase was reduced. Furthermore, the solid volume fraction of semi-solid non-dendritic structure decreased with increase in the shear rate. At the same time, the grain size of the primary α-phase changed slightly. A fine round granular solidified structure of 30–50 μm of prepared AZ91D magnesium semi-solid slurry was obtained. Finally, it was possible to successfully fabricate a 1.0 mm extremely thin-walled casting with a clear contour and good soundness.

Semisolid Casting of AlSi7Mg0.35 Alloy Produced by Low-Temperature Pouring

AlSi7Mg0.35 alloy was cast into permanent moulds using different pouring temperatures (725 to 625degreesC). As the pouring temperature decreased, the as-cast microstructure changed from a coarse dendritic structure, through fine equiaxed grains to fine rosette-like grains. The as-cast materials were then partially remelted and isothermally held at 580degreesC prior to semisolid casting into a stepped die. The feedstock material cast from a high temperature filled only half the die, with severe segregation and other defects. The low-temperature-poured material completely filled the die with negligible porosity. The quality of semisolid castings is significantly affected by the microstructure of the semisolid feedstock material that arises from a combination of as-cast and subsequent thermal treatment conditions. The paper describes (a) the influence of pouring temperature on the microstructure of feedstock; (b) microstructure evolution through remelting and (c) the quality of semisolid castings produced with this material. For A17Si0.35Mg alloy, low temperature pouring in the range of 625-650degreesC followed by suitable isothermal holding treatment can result in good quality semisolid casting.

Evaluation of the effect of vacuum on mold filling in the magnesium EPC process

The combination of magnesium alloys with the expendable pattern casting (EPC) process will bring a bright future for the application of magnesium alloys. Vacuum is a pre-requisite parameter in the EPC process of magnesium alloys, because without vacuum, the fluidity of the magnesium alloy in the EPC process is too poor to fill the mold completely, especially for the thin-section castings. In this investigation, the effect of vacuum on the fluidity of AZ91 magnesium alloy has been explored. A modified model has been presented to explain the effect of vacuum on mold filling, which was verified by optical microscopy. The results obtained indicate that vacuum is the most effective parameter in improving the fluidity, the effect of vacuum on the fluidity interacting strongly with the pouring temperature and coating. Vacuum greatly changes the mass and heat transfer in the EPC process. Vacuum may not only control the profile of the metal–foam interface, which will influence the mass transfer process, but may also greatly speed up the removal rate of pattern decomposition products at the metal–coating interface. It also changes the primary heat-transfer mode to heat convention, which has a great influence on the distribution of the casting temperature field and solidification process. The microstructures of castings cast with vacuum exhibit a fine grain size and a small amount of precipitated Mg 17Al 12, but vary insignificantly with the location in the castings.

Effect of process variables on microstructure and segregation in centrifugal casting of C92200 alloy

Tin bronzes containing lead and zinc have a wide variety of applications such as valves, taps, gears, bushes and bearings. Due to having elements of high difference in density and low solubility, tin bronzes are difficult to cast. Segregation normally occurs in centrifugal casting of these alloys. In this research, effect of process variables including pouring temperature, mould rotation speed and mould cooling rate on microstructure and segregation of lead and tin have been investigated. The results show that raising pouring temperature causes grain size and DAS to increase and segregation to intensify. Also, increasing mould rotation speed leads to high segregation and raising the grain size and DAS. Finally, increasing mould cooling rate, diminishes segregation of and reduces grain size and DAS.

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.

Statistical evaluation of strength for die-cast SiC p/Al alloy composites

Statistical evaluation for strength of die-cast SiC p/aluminum alloy composites has been performed in order to predict the reliability of composites. Die-casting was performed using the preheated die at the pouring temperature of 700°C. It was found that the SiC particulates were homogeneously distributed in Al alloy matrix, resulting from the refinement of cell size due to rapid cooling rate. The tensile strength of the as-die-cast composites was higher than that of the as-die-cast aluminum alloy. Furthermore, the tensile strength slightly increased with increasing SiC particulate volume fraction. However, the strength scattering of composites increased with increasing SiC particulate volume fraction. For the statistical evaluation of strength, the Weibull modulus of die-cast SiC p/Al alloy composites was 29.6 in Al matrix alloy, 22.2 and 14.2 for 10 and 20 vol.% SiC p, respectively.

A contribution to study of processes on the steel cast–sand mould contact surface during casting

The testings involved in this paper were part of a comprehensive research project conducted to find out what complex processes were taking place at metal–mould contact surface. These investigations are of particular importance for metal casting from relatively high melting temperature, such as that of steel (approximately 1600°C). Steel castings, in regard to their high manufactured temperature and other specifications in pouring, need a mould mixture of such good quality. The mould mixture, used for casting steel class DIN G-X 120 Mn 12, was based on the silica sand, and with water-glass as a binder and AlK(SO 4) 2 as an active component. This active component is, at pouring temperature of liquid steel, decomposed in the mould by thermal influence during pouring, crystallization and cooling the casting. In decomposition process of the active component, the gaseous products appear and the water-stream is generated from chemically bonded water. These processes are influencing the molten metal oxidation. The penetrated molten metal into the mould surface is oxidized, too. At the high melting temperature and in the presence of gaseous products, the silicates were formed in the contact zone between metal and sand mould mixture. The objective of these tests was to find out to what extent the composition of the mould mixture affects the formation process, shape, type and composition of the silicates.

Dendrite structure control in directionally solidified bronze castings

Tin bronze (Cu-8%Sn) was cast into cylindrical samples using a unidirectional solidification device monitored by thermocouples. Four cylindrical samples were obtained under four different experimental conditions where pouring temperature, heat extraction and addition of inoculant changed. Thermocouple temperature curves did not show any strong effect of inoculant additions, though, at the beginning of solidification, recalescence seemed to decrease with an increase in inoculant efficiency. Macrostructures of samples were examined on longitudinal sections and an increase in the columnar zone length was observed when the pouring temperature and the heat extraction flux were raised simultaneously. Secondary and primary dendrite plates were seen to form from the coalescence of secondary dendrite arms. Dendrite arm spacing was measured and related to the local solidification time and to the cooling rate, showing some agreement with relationships published in the literature.

Grain Formation in AlSi7Mg0.35 Foundry Alloy at Low Superheat

Hypoeutectic Al-Si alloys represent the most widely used alloy system for cast aluminium applications. This system has a unique behaviour with respect to grain formation where an increase in silicon content results in a transition to larger grain sizes after a minimum at an intermediate concentration. As a result of the already large solute content, grain refinement by solute additions is inefficient and nucleant particles from the common aluminium grain refiners are not as effective as in wrought alloys. However, casting conditions, such as a low pouring temperature, that promote the formation of wall crystals (ie. crystals nucleated in the thermally undercooled layer at or next to mould walls) are very effective in yielding a small grain size. This paper presents results of an investigation of the effect of low superheat and mould preheat temperature on grain size. It was found that pouring temperature controls the effectiveness of the wall mechanism while mould preheat has little effect until high preheat temperatures at which a large increase in grain size occurs. The observed changes in grain size are explained in terms of the balance between nucleation rate and survival rate of crystal nuclei resulting from changes in superheat and mould temperature.

Prevention of macrodefects in squeeze casting of an Al-7 wt pct Si alloy

The squeeze casting of an Al-7 wt pct Si alloy was carried out in order to investigate the conditions for the formation and the prevention of macrosegregation. The effects of process parameters such as applied pressure, die temperature, pouring temperature, delay time, degassing, and inoculation on the formation of macrosegregation were investigated, in correlation with the evolution of macrostructure and shrinkage defects. Three critical applied pressures were defined, based on the experimental results for the squeeze-cast Al-7 wt pct Si. The first is the critical applied pressure under which shrinkage defects form (PSC). The second is the critical applied pressure above which macrosegregates form (PMS). The third is the critical applied pressure above which and under which minor segregation forms. (Pm and PMS, respectively). With the concept of these three critical pressures, an experimental diagram describing the optimum process conditions was proposed for obtaining sound squeeze castings. It was concluded that sound castings without macrosegregation and shrinkage defects can only be obtained when the applied pressure is in the range where PSC < P<Pm (<PMS). Both degassing and inoculation treatments greatly enhanced the soundness of the castings. It was also found that the pouring temperature and the delay time should not exceed TD-critical and tD-critical, respectively, in order to achieve sound castings.

Application of hard coatings in aluminium die casting — soldering, erosion and thermal fatigue behaviour

In aluminium die casting, tools are exposed to erosion, corrosion and soldering due to the frequent contact of the tool surface to the casting alloy, to heat checking and gross cracking due to thermal fatigue and to oxidation due to high pouring temperatures. The gradual destruction of die surfaces during service decreases casting piece quality and limits die lifetime. Hard coatings based on nitrides or carbides of transition metals may protect the steel surface from erosion and soldering of aluminium and improve the resistance against thermal cracking. Thus, they may replace the thick oxide-based die coatings nowadays used in foundries. Within this study, results obtained on the performance of coatings deposited onto die-casting dies by magnetron sputtering and plasma-assisted chemical vapour deposition are presented and discussed. TiN, Ti(C,N), Ti(B,N), and (Ti,Al)(C,N) coatings deposited onto hot-working tool steel have been evaluated in practical die-casting service. Results obtained are compared with those of simulation tests using thermal cycling immersion tests in liquid aluminium, thermo-gravimetric analysis, and stress measurements during thermal cycling. Maximum lifetime of the coated casting die is achieved for careful optimization of hardness, adhesion, oxidation resistance and high temperature stability, and internal stresses.

Experimental and Numerical Investigations of Mould Filling of Thin Wall Horizontal Aluminium Castings

The application of Computational Fluid Dynamics (CFD) in the foundry practice is considered an essential tool to achieve a better understanding of the occurrence of casting defects introduced during mould filling of a casting. CFD is believed to be advantageous in predicting possible defect locations, pouring times, and the lowest possible casting temperature without the risk of cold shuts. Furthermore CFD may be used to optimize pouring system geometries. Contrary to experimental studies in, e.g., cold water similarity models, computer simulations allow for the flexible modification of the casting geometry and the pouring system, and for the inclusion of physical effects such as solidification and heat transfer. Computer modelling may lead to an improved recovery in cast shops without expensive trial-and-error procedures CFD simulations with the commercial FLOW-3D software were done on the mould filling conditions and gating systems for the manufacture of a horizontal horseshoe. These simulations were validated against data obtained with various experimental techniques. In the paper the following cases are considered: ○ flow patterns, i.e., the transient velocity field during mould filling, metal-air interface shapes, i.e., the position of the free surface and its shape due to surface tension ○ freezing lengths, i.e., the prediction of cold shuts in horizontal thin-wall casings Predicted flow patterns and interface shapes are overall agreement with experimental observations obtained from video registration and Particle Image Velocimetry (PIV). Freezing lengths that are experimentally found to depend linear on the pouring temperature, can be predicted with an accuracy of about 15 %.