Correlation between unsteady-state solidification conditions, dendrite spacings, and mechanical properties of Al-Cu alloys

The wide range of operational conditions existing in foundry and casting processes generates as a direct consequence a diversity of solidification microstructures. Structural parameters such as grain size and interdendritic spacings are strongly influenced by the thermal behavior of the metal/mold system during solidification, imposing, as a consequence, a close correlation between this system and the resulting microstructure. Mechanical properties depend on the microstructural arrangement defined during solidification. Expressions correlating the mechanical behavior with microstructure parameters should be useful for future planning of solidification conditions in terms of a determined level of mechanical strength, which is intended to be attained. In the present work, analytical expressions have been developed describing thermal gradients and tip growth rate during one-dimensional unsteady-state solidification of alloys. Experimental results concerning the solidification of Al-4.5 wt pet Cu and Al-15 wt pet Cu alloys and dendritic growth models have permitted the establishment of general expressions correlating microstructure dendrite spacings with solidification processing variables. The correlation of these expressions with experimental equations relating mechanical properties and dendrite spacings provides an insight into the preprogramming of solidification in terms of casting mechanical properties.31123167317

Experimental investigation of factors affecting surface quality of Al-Cu alloys ingots

For rapid chilling, the cast surface will often exhibit a particular group of defects characterized by ripples and laps. This work was carried out to experimentally investigate the influences of alloy solute content, melt superheat, transient metal/mold heat transfer coefficient and teeming speed on the surface quality of Al-Cu alloys ingots in the range of pure Al and the eutectic composition. The surface quality was shown to be enhanced by the increase of melt superheat and of teeming speed and the decrease of the metal/mold heat transfer efficiency. It was shown that the best surface quality is associated with a Cu content close to the maximum solidification range at about 5 wt.% Cu. (c) 2006 Elsevier B.V. All rights reserved.4314167120120

Determination of transient interfacial heat transfer coefficients in chill mold castings

The present work focuses on the determination of transient mold-environment and metal-mold heat transfer coefficients during solidification. The method uses the expedient of comparing theoretical and experimental thermal profiles and can be applied both to pure metals and metallic alloys. A solidification model based on the finite difference technique has been used to provide the theoretical results. The experiments were carried out by positioning the thermocouples in both metal and mold. The comparison between experimental and theoretical results is made by an automatic search of the best fitting among theoretical and experimental cooling curves simultaneously in metal and in mold. This has permitted the evaluation of the variation of heat transfer coefficients along the solidification process in unsteady state unidirectional heat flow of AI-Cu and Sn-Pb alloys, as well as the analysis of the effects of the material and the thickness of the mold and melt superheat. (C) 2001 Elsevier Science B.V. All rights reserved.3194167117418

Plate-like cell growth during directional solidification of a Zn-20wt%Sn high-temperature lead-free solder alloy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Although Zn-Sn alloys have suitable features for high temperature solders, as for example the absence of intermetallic compounds (IMCs) and relatively high melting temperatures, the control of the scale of the microstructure by adequate pre-programming of the solidification thermal parameters remains still a task to be accomplished. The present study focuses on the interrelation among hardness, microstructure features/segregation and solidification thermal parameters. An upward directional transient solidification apparatus was used in order to permit samples along a range of cooling rates to be obtained for such evaluation. The entire Zn-20wt%Sn alloy casting is characterized by a two-phase alternated structure, which resembles the morphology of a lamellar eutectic. Experimental growth laws having -1/2 and -1/4 exponents are proposed relating the interphase spacing to the growth rate and the cooling rate, respectively. The morphology and size of the Zn-rich plate-like cells, as well as the macrosegregation pattern are shown to affect the hardness. (C) 2013 Elsevier B.V. All rights reserved.1822936Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2012/08494-0

Interfacial heat transfer coefficients and solidification of an aluminum alloy in a rotary continuous caster

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The present Study describes the development of an experimental set-up representing the metal/mold system of a rotary continuous caster as part of a methodology, which connected to a numerical heat transfer model permits to determine transient metal/mold heat transfer coefficients, h, during solidification. By using this approach the variation or h along the different mold walls and the metal surface has been investigated by a method based on numerically calculated/experimental fit of thermal profiles (IHCP). The results have shown that the used methodology permits the characterization of h and may be used in the simulation of solidification in industrial processes. (c) 2008 Elsevier Ltd. All rights reserved.5241671451459Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)ALUBARFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Melt characteristics and solidification growth direction with respect to gravity affecting the interfacial heat transfer coefficient of chill castings

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)For purposes of an accurate mathematical modeling, it is essential to establish trustworthy boundary conditions. The heat transfer that occurs at the casting/mold interface is one of these important conditions, which is a fundamental task during unsteady solidification in permanent mold casting processes. This paper presents an overview of the inverse analysis technique (IHCP) applied to the determination of interfacial heat transfer coefficients, hi, for a number of alloy solidification situations. A search algorithm is used to find the transient metal/mold interface coefficient during solidification which is reported either as a function of the casting surface temperature or time. Factors affecting hi such as the direction of gravity in relation to the growth interface, the initial melt temperature profile, the wettability of the liquid layer in contact with the mold inner surface, were individually analyzed and experimental laws for hi have been established. (C) 2009 Elsevier Ltd. All rights reserved.30935923601Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAEPEX -UNICAMPFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq