7 research outputs found

    Influence of solidification thermal parameters on the columnar to equiaxed transition of Sn-Pb alloys solidified under unsteady-state conditions

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    This work carry out a theoretical experimental study about the influence of solidification thermal parameters on the columnar to equiaxed transition of Sn 5%Pb, Sn 15%Pb, and Sn 20% Pb and Sn 25% Pb alloys during the horizontal unidirectional solidification process cooled by water which considers the solute convection effects. The tip growth rates and cooling rates have been experimentally calculated and the obtained results are compared with those of a numerical model. The columnar to equiaxed transition position is determined through the macrostructure characterization of the studied alloys. The experimental results have shown that the thermosolutal convection influences the CET occurrence. Finally, a comparative experimental study is done for the studied alloys when directionally solidified in different water-cooled systems.CEFET/PA - Centro Federal de Educação Tecnológica do ParáO principal objetivo deste trabalho é desenvolver um estudo teórico/experimental sobre a influência dos parâmetros térmicos de solidificação (V L e T) na transição colunar/equiaxial das ligas Sn 5%Pb, Sn 15%Pb, Sn 20%Pb e Sn 25%Pb sob condições de solidificação unidirecional horizontal refrigerada à água. Inicialmente, são calculadas experimentalmente as velocidades da isoterma líquidus e as taxas de resfriamento das ligas em questão cujos resultados são comparados com as previsões teóricas de um modelo numérico. Em seguida, a posição da transição colunar/equiaxial é determinada por meio da análise macroestrutural assim como são avaliados os efeitos impostos por correntes convectivas devido ao efeito do soluto no comportamento da transição colunar/equiaxial das referidas ligas. Finalmente, é realizado um estudo experimental comparativo para as ligas estudadas quando solidificadas unidirecionalmente em diferentes sistemas refrigerados à água

    Analysis of microestrutural evolution and formation of macrosegregation and microparasity in the unidirectional transient solidification of ternary Al-Cu-Si alloys

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    Orientadores: Amauri Garcia, Ivaldo Leão FerreiraTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: As ligas fundidas de alumínio vêm desempenhando um papel importante no crescimento da indústria metal-mecânica. Hoje, essas ligas são produzidas em vários sistemas e dezenas de composições. Destacamos as ligas do sistema ternário Al-Cu-Si que apresentam excelente fluidez, alta resistência mecânica e baixo peso, o que as tornam uma escolha adequada como ligas de fundição, sendo amplamente aplicadas na indústria automotiva e aeroespacial. Tais características e o elevado grau de destaque dessas ligas no campo científico e tecnológico têm despertado o interesse de pesquisadores para o desenvolvimento de trabalhos que visam a investigação da evolução microestrutural, formação de macrossegregação e porosidade na solidificação. Neste trabalho, a caracterização e quantificação microestrutural e suas correlações com os parâmetros térmicos da solidificação de ligas Al-Cu-Si são investigadas juntamente com a macros segregação e formação de porosidade tanto através de simulações numéricas quanto através de experimentos de solidificação direcional em regime transitório. A microestrutura dendrítica foi caracterizada por técnicas tradicionais de metalografia para as ligas Al6Cu1Si e Al6Cu4Si e a quantificação dos espaçamentos dendríticos realizada por metodologias consagradas na literatura. Os resultados mostram que a adição de silício na composição da liga diminui os espaçamentos dendríticos primários e secundários quando comparados com a liga binária Al-Cu de mesmo teor de cobre. São propostas leis experimentais de evolução dos espaçamentos dendríticos como função da taxa de resfriamento ( ? ) e da velocidade de deslocamento da isoterma liquidus (VL), na forma 'lambda IND. 1' = C ( ? )-0,55, 'lambda IND. 2' = C ( ? )-0,33 'lambda IND. 3' = C ( ? )-0,55 para os espaçamentos primários, secundários e terciários respectivamente. Os valores experimentais dos espaçamentos dendríticos secundários foram comparados com o único modelo teórico de crescimento dendrítico existente na literatura para ligas multicomponentes. O diagrama de fases ternário, bem como os caminhos de solidificação de ambas as ligas analisadas, e propriedades termofísicas necessárias para simulações numéricas foram determinadas através do software Thermo-Calc. Os perfis experimentais e numéricos de macrossegregação, bem como as densidades teóricas e aparentes são apresentados em função do comprimento dos lingotes. Os perfis de soluto durante a solidificação unidirecional transitória das ligas foram calculados levando-se em conta transformações de fase secundárias que ocorrem ao longo do referido sentido de solidificação. A microporosidade foi obtida experimentalmente através de um procedimento picnométrico. Também é mostrado que o uso de uma chapa molde de aço carbono induz um aumento atípico na fração de poros próximos à superfície resfriada do lingote, o que é causado por uma maior concentração de ferro provocada pelo fluxo difusivo deste elemento da chapa molde para a superfície do lingoteAbstract: Aluminum alloys castings had a fundamental role in the growth of the metal-mechanics industry. Nowadays these alloys are supplied in a wide range of chemical compositions. We highlight the Al-Cu-Si ternary system because of particular outstanding properties such as high mechanical strength, low weight and very good fluidity. These qualities make them a good choice for applications in the automotive and aerospace industry. The potential of such alloys has attracted much attention of researchers with a view to investigating the microstructure evolution, and the formation of macrosegregation and porosity during the solidification process. In the present work, the microstructures of Al-Cu-Si alloys are characterized and correlated with solidification thermal parameters. The evolutions of macrosegreation and porosity during transient solidification are also examined both experimentally and by numerical simulations. The dendritic microstructure has been characterized using current metallographic techniques for both Al6Cu1Si e Al6Cu4Si alloys and the interdendritic spacings were measured by methods found in the literature. The results have shown that the addition of silicon to the alloy composition decreases the primary and secondary dendritic spacing when compared with those of an Al6Cu alloy. Experimental laws describing the evolution of dendritic spacings with the cooling rate ( ? ) and the velocity of the liquidus isotherm (VL) are proposed, i.e., 'lambda IND. 1' = C ( ? )-0,55, 'lambda IND. 2' = C ( ? )-0,33 and 'lambda IND. 3' for the primary, secondary and tertiary dendritic spacings, respectively. The experimental results of secondary dendritic spacings have been compared with the predictions of the only theoretical model existing in the literature for dendritic growth of multicomponent alloys. The Thermo-Calc software has been used to yield the tertiary phase diagram, thermophysical properties and the solidification path for both alloys. The experimental and numerical macrosegregations profiles, as well as the theoretical and apparent densities are presented as a function of the castings lenghts. The solute profiles that occur during the transient unidirectional solidification were simulated taking into account the formation of secondary phases during solidification. The microporosity was determined using a pyknometry procedure. The work also shows that the use of a carbon steel chill plate induces an abnormal increase in porous fraction at regions close to the casting cooled surface caused by a higher iron content, due to diffusive flux of iron from the chill steel plate toward the casting surfaceDoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânic

    The columnar to equiaxed transition of horizontal unsteady-state directionally solidified Al-Si alloys

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    Experiments were conducted to investigate the influence of thermal parameters on the columnar to equiaxed transition during the horizontal unsteady-state directional solidification of Al-Si alloys. The parameters analyzed include the heat transfer coefficients, growth rates, cooling rates, temperature gradients and composition. A combined theoretical and experimental approach is developed to determine the solidification thermal variables considered. The increasing solute content in Al-Si alloys was not found to affect significantly the experimental position of the CET which occurred for cooling rates in the range between 0.35 and 0.64 K/s for any of three alloy compositions examined. A comparative analysis between the results of this work and those from the literature proposed to analyze the CET during upward vertical solidification of Al-Si alloys is reported and the results have shown that the end of the columnar region during horizontal directional solidification is abbreviated as a result of about six times higher thermal gradient than that verified during upward unidirectional solidification of alloys investigated

    Influence of upward and horizontal growth direction on microstructure and microhardness of an unsteady-state directionally solidified Al-Cu-Si alloy

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    In order to analyze the effect of the growth direction on dendrite arm spacing (λ1) and microhardness (HV) during horizontal directional solidification (HDS), experiments were carried out with the Al-3wt.%Cu-5.5wt.%Si alloy and the results compared with others from the literature elaborated for upward directional solidification (UDS). For this purpose, a water-cooled directional solidification experimental device was developed, and the alloy investigated was solidified under unsteady-state heat flow conditions. Thermal parameters such as growth rate (VL) and cooling rate (TR) were determined experimentally and correlations among VL, TR, λ1 and HV has been performed. It is observed that experimental power laws characterize λ1 with a function of VL and TRgiven by: λ1=constant(VL)-1.1 and λ1=constant(TR)-0.55. The horizontal solidification direction has not affected the power growth law of λ1 found for the upward solidification. However, higher values of λ1 have been observed when the solidification is developed in the horizontal direction. The interrelation of HV as function of VL, TR and λ1 has been represented by power and Hall-Petch laws. A comparison with the Al-3wt.%Cu alloy from literature was also performed and the results show the Si element affecting significativaly the HV values

    Solidification thermal parameters and dendritic growth during the horizontal directional solidification of Al-7wt.%Si alloy

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    The main purpose of this work is to investigate the influence of thermal parameters such as growth rate (V L) and cooling rate (T R) on the primary dendrite arm spacings (λ1) during the horizontal transient directional solidification of Al-7wt.%Si hypoeutectic alloy. The primary dendrite spacings were measured along the length of the samples and correlated with these thermal parameters. The variation of dendrite spacings is expressed as a power law function of V L and T R given by the formulas λ1 = 55(V L)-1.1 and λ1 = 212 (T R)-0.55, respectively. A comparative study between the results of this work and those from the literature proposed to investigate these dendrite spacings during the upward and downward vertical directional solidification of Al-7wt.%Si alloy is also conducted. Finally, the experimental data are compared with some predictive dendritic models from the literature

    Influence of upward and horizontal growth direction on microstructure and microhardness of an unsteady-state directionally solidified Al-Cu-Si alloy

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    In order to analyze the effect of the growth direction on dendrite arm spacing (λ1) and microhardness (HV) during horizontal directional solidification (HDS), experiments were carried out with the Al-3wt.%Cu-5.5wt.%Si alloy and the results compared with others from the literature elaborated for upward directional solidification (UDS). For this purpose, a water-cooled directional solidification experimental device was developed, and the alloy investigated was solidified under unsteady-state heat flow conditions. Thermal parameters such as growth rate (VL) and cooling rate (TR) were determined experimentally and correlations among VL, TR, λ1 and HV has been performed. It is observed that experimental power laws characterize λ1 with a function of VL and TRgiven by: λ1=constant(VL)-1.1 and λ1=constant(TR)-0.55. The horizontal solidification direction has not affected the power growth law of λ1 found for the upward solidification. However, higher values of λ1 have been observed when the solidification is developed in the horizontal direction. The interrelation of HV as function of VL, TR and λ1 has been represented by power and Hall-Petch laws. A comparison with the Al-3wt.%Cu alloy from literature was also performed and the results show the Si element affecting significativaly the HV values
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