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1

Estimation Of Cooling Rates In Suction Casting And Copper-Mould Casting Processes

Kozieł T.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 2A

767--771

EN

The cooling rates associated with suction and copper-mould casting of ø2, ø3 and ø5 mm rods made in Fe-25wt%Ni and Al-33wt%Cu alloys were determined based on their cellular and lamellar spacings, respectively. The work showed that the temperature profile in cylindrical samples can not be determined merely by microstructural examination of eutectic sample alloys. A concave solidification front, as a result of eutectic transformation, caused decrease of a lamellar spacing while approaching to the rod centre. The minimum axial cooling rates, estimated based on the cellular spacing in the Fe-25wt%Ni alloy, were evaluated to be about 200 K/s for both ø2 and ø3 mm and only 30 K/s for the ø5 mm suction cast rods. The corresponding values were slightly lower for the copper-mould cast rods.

PL

Na podstawie analizy wielkości dendrytów komórkowych w stopie Fe-25Ni i odległości międzypłytkowych w stopie Al-33Cu zostały oszacowane szybkości chłodzenia w trakcie odlewania stopów metodami suction casting i copper-mould casting. Badania wykazały, że rozkład szybkości chłodzenia w cylindrycznych próbkach nie może być oszacowany w stopach z krystalizacją eutektyczną. W tym przypadku bowiem dochodzi do zmniejszania odległości międzypłytkowej w miarę zbliżania się do osi pręta, ze względu na wklęsły charakter frontu krystalizacji. Minimalna szybkość chłodzenia w osi prętów odlanych za pomocą metody suction casting, wyznaczona w oparciu o pomiary wielkości dendrytów komórkowych w stopie Fe-25wt%Ni, wyniosła ok. 200 K/s dla stopów o średnicy ø2 i ø3 mm, i tylko 30 K/s dla stopów o średnicy ø5 mm. W przypadku stopów odlanych metodą copper-mould casting oszacowane wartości były nieznacznie mniejsze.

2

Coupled and competitive eutectic growth

Trepczyńska-Łent M.

Archives of Foundry Engineering

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2011

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Vol. 11, iss. 3 spec.

237--240

EN

A description of the competitive growth is presented in the paper. The description is associated with the competition between eutectic structure and primary phase formation. A coupled zone for the eutectic solidification is drawn in the phase diagrams. The coupled zone is shown as a range of solute concentration versus under-cooling to justify the formation of the eutectic structure, exclusively. Interface growth temperatures of the single and coupled eutectic are illustrated schematically as a function of growth rates at a given composition Co.

3

Evaluation of Al-5Ti-1B and Al-10Sr in LM6 sand castings

Lim Y. P.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 34, nr 1

71-78

EN

Purpose: of this paper is to study the separate effects of grain refiner and modifier on the metallurgical properties of LM6 sand castings. The research aims to determine how grain refiner and modifier will influence the microstructure of LM6 sand casting and the associated mechanical properties of hardness, ultimate tensile strength and engineering strain. Design/methodology/approach: A grain refiner consists of 0.5wt% Al-5Ti-1B and a modifier consists of 0.5wt% Al-10Sr have been introduced separately into the melt of hypoeutectic LM6 Al-Si alloy to produce slab castings by CO2 sand casting process. The geometry of the slab casting is designed to have different section moduli to induce directional solidification. Temperature profile of cooling process is taken to correlate between the section modulus and cooling rate. This enables the effect of cooling rate on microstructure and mechanical properties to be studied for grain refined and modified LM6 sand castings. Findings: The significant finding is that a nearly full eutectic solidification at 540°C is achieved in the Sr-modified casting with faster cooling rates than those of solely grain-refined and original LM6. The hardness and ultimate tensile strength can be improved respectively between 20~40% and 11~18% by Al-10Sr modifier. It is observed that the Al-5Ti-1B grain refiner and Al-10Sr modifier increase the strain at UTS by 11% and 22% respectively. The metallographic observations show that the eutectic phase is finer and in fibrous form in the Sr-modified LM6. Research limitations/implications: Further research can study a wider range of inoculant percentage. Practical implications: This eutectic solidification at 540°C achieved in Sr-modified LM6 is lower than the solidus temperature of LM6 to reduce superheat and save electrical energy consumption while ensuring complete liquid mould filling. Originality/value: This is the original work of slab casting of LM6 and the effects of Sr modifier and TiB grain refiner on its metallurgical properties.

4

Eutectic solidification as explained by the thermodynamics of irreversible processes

Wołczyński W., Guzik E.

Archives of Foundry Engineering

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2009

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Vol. 9, iss. 1

113-116

EN

The grain size diameter is the main parameter characterizing a given metallic alloy. In the case of Al-Si or Fe-C eutectic alloy the average inter-lamellar spacing is a good parameter which seems to be adequate to describe this irregular structure. To define the average inter-lamellar spacing the regular areas within generally irregular structure has been distinguished. It has been postulated that the formation of regular structure could be related to the minimum entropy production criterion. From the other side the maximum destabilization of the non-faceted phase interface could be referred to marginal stability. The criterion of minimum entropy production allows to formulate the growth law for regular lamellar structure solidifying under stationary state. It defines the regular eutectic spacing versus growth rate. The marginal stability concept allows to define the maximum wavelength which can be developed at the solid / liquid interface of non-faceted (Al) phase. It defines the maximum spacing within irregular structure taking into account the wavelength of instability (marginal stability) created at the non-faceted phase interface. An average inter-lamellar spacing results from the relationship formulated on the basis of both spacings. It should be emphasized that both conditions (criteria) are deduced from the thermodynamics of irreversible processes. The simplified scheme of irregular structure incorporates, additionally the intermediate lamella of faceted phase that is also taken into account in the definition of average inter-lamellar spacing, [...] . The intermediate morphology existing between two distinguished distances is treated as being under oscillation between stationary state and marginal stability. The state of marginal stability is defined by a vanishing excess entropy production. Therefore, it is suggested that the structural oscillation takes place between an attractor and point of bifurcation in the system.