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Lashkari, Omid. "The rheological behavior of semi-solid A356 alloy." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2006. http://theses.uqac.ca.
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Thèse (D.Eng.) -- Université du Québec à Chicoutimi, 2006.La p. de t. porte en outre: Dissertation presented to the University of Quebec at Chicoutimi in partial fulfilment of the requirement for the degree of doctor of philosophy in engineering. CaQCU Bibliogr.: f. 177-184. Document électronique également accessible en format PDF. CaQCU
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Moller, H., G. Govender, and W. E. Stumpf. "Improvement of the T6 heat treatment of rheocast alloy A356." Journal for New Generation Sciences, Vol 8, Issue 2: Central University of Technology, Free State, Bloemfontein, 2010. http://hdl.handle.net/11462/561.
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Published ArticleThe heat treatment cycles that are currently applied to semi-solid processed components are mostly those that are in use for traditional dendritic alloys. These heat treatments are not necessarily the optimum heat treatments for SSM processing. The T6 heat treatment of aluminium alloys is a relatively expensive process and a reduction in treatment times would be advantageous. In order to improve the T6 heat treatment cycle for rheocast alloy A356, the effect of various parameters on the quality index were investigated. These included solution treatment time, natural aging time, artificial aging temperature and artificial aging time.
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Yi, Jianzhang. "Effect of microstructure and defects on the fatigue behaviour of cast A356-T6 aluminium-silicon alloy." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405613.
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Angeloni, Mauricio. "Fatigue life evaluation of A356 aluminum alloy used for engine cylinder head." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2011. http://tel.archives-ouvertes.fr/tel-00661622.
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The studied material is an A356 Al alloy, used to produce engine cylinder heads for the automotive industry by die casting process. The material displays a quite coarse dendritic microstructure in a eutectic matrix, with a mean grains size of 25 microns, intemetallic precipitates and porosities. The tensile properties are strongly affected by testing temperature, with a quite sensitive drop of the Young's modulus, the Yield stress as the temperature was raised. The isothermal fatigue life dropped of markedly (approximately 10 times) when the testing temperature is raised from 120 to 280 °C, under strain control. From the themomechanical in-phase cyclic tests, with temperature varying from (120 to 280 oC), it was possible to observe that life is quite similar to the isothermal fatigue test at 280 oC. In this case, the more sensitive damage caused the in-phase mechanical and thermal cycle take place at the highest temperature. Relaxation tests indicated two distinct behaviors, with the temperature of 240°C being a threshold. At lower temperatures, the material hardens cyclically whereas it softens cyclically at higher temperatures. From the fatigue crack growth results, it was observed that temperature and wave shape has a strong influence on the crack growth rate as well as on the stress intensity threshold. Considering sinusoidal wave shape (10 Hz), as the temperature increased the DKth decreased and the crack propagation rate increased. However, the rate as da/dN change with temperature is quite similar, as an indicative that the micromechanism of crack growth has not changed due to the high frequency used, and it was due only to loss of mechanical strength. An elastic-visco-plastic non-isothermal constitutive law was identified for the material. For the cast material studied in this work, the mechanical behavior parameters are statistically distributed. However, it was shown that the model was able to reproduce, with a reasonable approximation, the stress - strain relationship at different temperatures, for the isothermal and anisothermal cases.
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Sumartha, Yusuf 1972. "Fluidity of rheocast A356 aluminum alloy." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10231.
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Nelaturu, Phalgun. "Fatigue Behavior of A356 Aluminum Alloy." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849720/.
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Metal fatigue is a recurring problem for metallurgists and materials engineers, especially in structural applications. It has been responsible for many disastrous accidents and tragedies in history. Understanding the micro-mechanisms during cyclic deformation and combating fatigue failure has remained a grand challenge. Environmental effects, like temperature or a corrosive medium, further worsen and complicate the problem. Ultimate design against fatigue must come from a materials perspective with a fundamental understanding of the interaction of microstructural features with dislocations, under the influence of stress, temperature, and other factors. This research endeavors to contribute to the current understanding of the fatigue failure mechanisms. Cast aluminum alloys are susceptible to fatigue failure due to the presence of defects in the microstructure like casting porosities, non-metallic inclusions, non-uniform distribution of secondary phases, etc. Friction stir processing (FSP), an emerging solid state processing technique, is an effective tool to refine and homogenize the cast microstructure of an alloy. In this work, the effect of FSP on the microstructure of an A356 cast aluminum alloy, and the resulting effect on its tensile and fatigue behavior have been studied. The main focus is on crack initiation and propagation mechanisms, and how stage I and stage II cracks interact with the different microstructural features. Three unique microstructural conditions have been tested for fatigue performance at room temperature, 150 °C and 200 °C. Detailed fractography has been performed using optical microscopy, scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD). These tools have also been utilized to characterize microstructural aspects like grain size, eutectic silicon particle size and distribution. Cyclic deformation at low temperatures is very sensitive to the microstructural distribution in this alloy. The findings from the room temperature fatigue tests highlight the important role played by persistent slip bands (PSBs) in fatigue crack initiation. At room temperature, cracks initiate along PSBs in the absence of other defects/stress risers, and grow transgranularly. Their propagation is retarded when they encounter grain boundaries. Another major finding is the complete transition of the mode of fatigue cracking from transgranular to intergranular, at 200 °C. This occurs when PSBs form in adjacent grains and impinge on grain boundaries, raising the stress concentration at these locations. This initiates cracks along the grain boundaries. At these temperatures, cyclic deformation is no longer microstructure- dependent. Grain boundaries don’t impede the progress of cracks, instead aid in their propagation. This work has extended the current understanding of fatigue cracking mechanisms in A356 Al alloys to elevated temperatures.
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Hernández, Paz Juan Francisco. "Heat treatment and precipitation in A356 aluminum alloy." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19547.
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Al-7%Si-0.3Mg (A356) foundry alloy is strontium modified and heat treated in order to obtain optimum mechanical properties. To date, the role that strontium modification plays in the precipitation process during the heat treatment is not well understood. The objective of the present work is to obtain a better understanding of the effect that strontium modification and heat treatment parameters exert on the properties of heat-treated Al-7%Si-0.3Mg alloy. The investigation consisted of a systematic measurement of the electrical conductivity and matrix microhardness of heat-treated coupons under different process conditions. Tensile properties were also measured and a transmission electron microscopy study of critical samples was done. The results obtained in this work indicate that the heat treatment of this alloy can be optimized. Solution heat treatment and artificial aging can be reduced and natural aging manipulated. The use of a continuous heating artificial aging is proposed. During the heat treatment of the A356 alloy under certain conditions not only does the precipitation of the Mg2Si occur, but also that of silicon. It was found that strontium modification does not influence the precipitation kinetics of the Mg2Si, but it does retard the precipitation of the silicon out of the matrix.
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Pekgüleryüz, Mihriban Özden. "Strontium dissolution in liquid aluminum and A356 alloys." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75438.
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The dissolution mechanism and kinetics of a number of strontium master alloys in liquid aluminum and A356 alloys have been investigated. The dissolution behaviour of the strontium alloys was found to show marked differences depending on strontium content. Dilute strontium alloys containing less than 63 weight percent Sr were observed to exhibit simple dissolution in both melts. The dissolution rate and the recoveries of these alloys were found to increase with increasing melt temperature. Over the temperature interval of 675-775$ sp circ$C dissolution was determined to be mass-transfer controlled with associated activation energies of 10-20 kcal/mole. Experimental rate constants for dissolution showed good agreement with a mass transfer correlation expressed as k = (0.67(Gr.Sc)$ sp{1/4}$ + 0.58(h/r)) (D/h). The dissolution of high strontium master alloys $(>$63 wt. pct. Sr), unlike the dilute alloys, was accompanied by the formation of various intermetallics. Additions at low melt temperatures yielded the exothermic formation of those intermetallics that have the lowest Sr content as seen in the relevant phase diagram, i.e., SrAl$ sb4$ in liquid Al and SrAl$ sb2$Si$ sb2$ in liquid A356. Due to low reaction rates at these low melt temperatures, these intermetallics formed as dispersed particles that could easily dissolve in the melt yielding high recoveries. At high melt temperatures, the associated chemical reactions yielded, as products, the higher Sr intermetallics which formed with little or no exothermicity. These intermetallics were observed to be scarcely soluble in the melt resulting in low strontium recoveries. The dissolution times of these alloys were found to show good agreement with calculated values based on a two-stage dissolution model comprising an initial exothermic reaction period and a subsequent free dissolution period. The strontium master alloys were classified in two groups; the high Sr alloys that are efficient at low temperatures of 675-7
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Silva, Beethoven Max Alves da. "Influencia da microestrutura inicial e material de molde na tixoconformação da liga A356." [s.n.], 2004. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263687.
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Orientador: Maria Helena RobertDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Neste trabalho investiga-se a influência da microestrutura inicial e do material do molde na tixoconformação da liga A356. São produzidas e testadas em operações de tixoforjamento pastas obtidas por três distintos processos: fusão parcial controlada de estrutlJ'aS dendríticas grosseiras, fusão parcial controlada de estruturas ultra-refinadas e pastas obtidas por agitação mecânica do líquido durante solidificação. É produzido ainda um compósito A356 + Ab03 obtido por compofundição. Os tixoforjados foram submetidos à análise metalográfica para caracterização microestrutural, medindo-se a fração da fase primária e o tamanho médio de glóbulo ou roseta da fase sólida. Os resultados obtidos mostram a viabilidade da utilização de moldes não metálicos e operações de tixoconformação com produtos de bom acabamento superficial e dimensional. As forças de tixoforjamento são dependentes da condição inicial da matéria-prima, de forma que forças maiores são requeridas com o aumento do parâmetro microestrutural básico (espaçamento interdendrítico, tamanho de glóbulo e tamanho de roseta) da matéria-prima
Abstract: This research aims the influence of initial microstructure and die material on thixofonning of A356 alloy. Obtained slurries are produced and tested in thixoforging operation by three distinct processes: controlled partial melting of coarse dendritic structures, controlled partial melting of ultra-refined structures and obtained slurries by liquid mechanical stirring during solidification. It is still produced a composite A356 + AbO:i obtained by compocasting. Thixoforged samples were submitted to metalographic analysis for microstructural characterisation, measuring the primary phase fraction and globule average size or 50lid phase rosette. Obtained results showed the viability of non-metallic dies in thixoforming operations with good superficial and dimensional finishing produds. Thixoforging forces are dependent on initial condition of raw material, 50 that higher forces are required with the increasing of basic microstructural parameter Onterdentritic spacing, globule size and rosette size) of raw material
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
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Campo, Kaio Niitsu 1988. "Uso da extrusão em canal angular na produção da liga A356 para tixoconformação." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265929.
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Orientador: Eugênio José ZoquiDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Este trabalho investigou o uso da extrusão em canal angular (ECA) na produção de matéria-prima para tixoconformação visando à obtenção de uma rota simples e eficiente na formação de microestruturas globulares. Para tanto, uma liga de alumínio A356 foi submetida a um único passe ECA e, em seguida, reaquecida ao estado semissólido a 580°C. Dessa forma, pôde-se determinar a evolução morfológica e os mecanismos envolvidos na formação da pasta metálica, a influência do tratamento isotérmico na evolução microestrutural no estado semissólido, o comportamento de deformação durante a compressão a quente e o comportamento mecânico em tração do material tixoconformado. Os resultados indicaram que apenas um passe ECA foi suficiente para gerar uma pasta metálica refinada e globular apenas com o reaquecimento da matéria-prima. O engrossamento da microestrutura durante o tratamento isotérmico foi controlado principalmente pelo mecanismo de Ostwald ripening, fato comprovado pelo baixo valor da constante taxa de engrossamento K, o que mostrou a estabilidade dessa pasta no estado semissólido. As amostras exibiram comportamento tixotrópico típico com baixos valores de viscosidade aparente, na faixa de 10^2 a 10^3 Pa.s para as taxas de cisalhamento testadas. Por fim, as amostras tixoconformadas apresentaram valores de ductilidade e resistência à tração superiores aos das amostras fundidas e deformadas por um passe ECA
Abstract: This work investigated the use of equal channel angular pressing (ECAP) for the production of raw materials for thixoforming in order to obtain a simple and efficient processing route to generate globular microstructures. Therefore, an A356 aluminum alloy was processed by one ECAP pass, and then reheated to the semisolid state up to 580°C. Thus, it was possible to determine the morphological evolution and mechanisms involved in the formation of the semisolid slurry, the influence of isothermal treatment on microstructural evolution in the semisolid state, the deformation behavior during hot compression tests and the tensile properties of the thixoformed material. The results indicated that a single ECAP pass was sufficient to promote a refined and globular semisolid slurry. Microstructure coarsening during the isothermal treatment was mainly controlled by Ostwald ripening, which was verified by the low rate constant K, showing the stability of the reheated material in the semisolid state. The samples exhibited typical thixotropic behavior with low apparent viscosity ranging from 10^2 to 10^3 Pa.s over the applied shear rates. Finally, the thixoformed samples exhibited values of ductility and tensile strength superior to the as-cast and ECAPed samples
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica
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Silva, Cássia Cavalcanti. "Efeito de inoculantes para refino de grão e modificador de eutético na curva de resfriamento da liga A356 e da liga A356 reciclada /." Guaratinguetá, 2016. http://hdl.handle.net/11449/141999.
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Orientador: Carlos KiyanCoorientador: Alexandre Zirpoli Simões
Banca: Ana Paula Rosifini Alves Claro
Banca: Luis Rogério de Oliveira Hein
Banca: Mirian de Lourdes Noronha Motta Melo
Banca: Olivério Moreira Macedo Silva
Resumo: A liga AA 356 é uma liga Al-Si amplamente utilizada tanto na indústria automobilística como na aeronáutica. Para melhorar suas propriedades mecânicas, são usados inoculantes para o refino de grão e para modificação eutética. Os componentes solidificados em moldes metálicos, que são mais eficientes na extração de calor, em geral, têm propriedades mecânicas superiores àqueles solidificados em moldes de areia que apresentam uma menor taxa de extração de calor. A curva de resfriamento que é uma curva da temperatura em função do tempo obtida da extremidade de um termopar localizado no centro do molde e conectado a um sistema de aquisição de dados é uma ferramenta que permite avaliar tanto o refino de grão quanto a modificação eutética. Essa ferramenta permite observar também a formação de fases intermetálicas, e é influenciada por fatores como a taxa de resfriamento. A primeira derivada da curva de resfriamento que representa a taxa de resfriamento é parte da ferramenta, pois melhora a precisão dos dados obtidos com a curva de resfriamento. Para o desenvolvimento desse trabalho foram preparados lingotes variando-se o material do molde (areia e aço), o teor de modificador de eutético e a adição de refinador de grão, ambos na forma de ligas-mãe (ante-liga) Al-10Sr e Al-5Ti-1B, respectivamente. Os valores para traçar as curvas de resfriamento foram obtidos monitorando a temperatura do metal desde o vazamento até sua completa solidificação e posterior resfriamento. Amostras do materia... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The alloy AA 356 is an Al-Si alloy widely used in the automotive and aeronautics industry. To improve the mechanical properties of this alloy inoculants are used to grain refine and eutectic modification. The solidified components in metal mold, with a higher heat extraction rate, generally have mechanical properties superior to those solidified in sand mold with a lower heat extraction rate. The cooling curve is a curve of temperature versus time obtained in the end of a thermocouple located in the center of the mold and connected to a data acquisition system. It is a tool to evaluate both the grain refinement as the eutectic modification. This tool also can also be used to observe the formation of intermetallic phases, and is influenced by factors such as the cooling rate. The first derivative of the curve representing the cooling rate is part of the tool because it improves the accuracy of the data obtained from the curve. For the development of this work ingots were prepared varying the mold material (sand and steel), the content of eutectic modifier and the grain refiner addition, both in the form of master alloys Al-10Sr and Al-5Ti-1B, respectively.The data for plotting the cooling curves were obtained experimentally during solidification; Samples of the material were prepared for metallography and macrostructure and microstructure images were obtained. Through microstructure images obtained with conventional etching and deep etching. Porosity fraction area was measure... (Complete abstract click electronic access below)
Doutor
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Chen, Hu. "L'effet du taux de refroidissement, modification au strontium, traitement thermique du liquide et la mise en solution sur les caractéristiques des particules du silicium eutectique et les propriétés de traction de l'alliage A356 /." Thèse, Chicoutimi : Université du Québec à Chicoutimi, 2005. http://theses.uqac.ca.
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Colley, Leo John. "Microstructure-property models for heat treatment of A356 aluminum alloy." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/33142.
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The evolution of microstructure and mechanical properties during heat treatment of an industrially-cast A356 aluminum alloy was studied in an extensive experimental investigation. The temperature ranges of interest were; solution treatment at 500-560°C, natural ageing at room temperature, and artificial ageing at 150-200°C. The changes in dendritic composition and eutectic morphology due to solution treatment were quantified by microprobe and image analysis for a wide range of processing conditions. Subsequently, a microstructure model for solution treatment was constructed using sub-models for; i) the dissolution of Mg₂Si particles, ii) the fragmentation of eutectic fibres, and iii) the coarsening of the fragmented eutectic. For the ageing investigations, characterisation of mechanical properties was done by hardness and tensile testing, and the kinetics of precipitation was determined by an isothermal calorimetry technique. A model to predict the evolution of yield strength during artificial ageing was developed based on established physical theories. A yield strength model for natural ageing was also proposed using data from isothermal calorimetry tests performed close to room temperature. Two model Al-Si-Mg alloys were investigated in order to extend both ageing models to include the effects of; i) alloy chemistry, ii) incomplete solution treatment and iii) natural ageing prior to artificial ageing. The validity of the models was verified using independent experimental measurements and literature data, and they were subsequently used as a tool to identify potential optimisation strategies for industrial heat treatment processes. The linkages between the models revealed details of processing challenges arising from the interdependence of the heat treatment stages, such as reduced strengthening during ageing due to incomplete solution treatment, and delayed strengthening during artificial ageing as a result of prior natural ageing.
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Hashemi-Ahmady, M. "Solidification, structure and mechanical properties of A357 aluminium alloy." Thesis, University of Southampton, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381127.
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wu, chang-kai. "Evaluation of Distortion and Residual Stresses Caused by Heat Treatment of Cast Aluminum Alloy Components." Digital WPI, 2009. https://digitalcommons.wpi.edu/etd-theses/417.
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The objective of this research was to develop and verify a mathematical model that enables the prediction of the effects of heat treatment on cast aluminum alloy components. The model, which uses the commercially available software (ABAQUS), predicts dimensional changes, distortion, and residual stresses in heat treated components. An extensive database is developed for an example aluminum alloy (A356) and includes the mechanical, physical, and thermal properties of the alloy all as functions of temperature. The database is obtained through calculations and measurements made on A356 alloy specimens. In addition, boundary conditions ¨C in the form of heat transfer coefficients for each of the heat treatment steps - are obtained from measurements performed with a special quenching system developed at the Center for Heat Treating Excellence at WPI. The database and boundary conditions were used in the software to predict the dimensional changes, distortions, and residual stresses that develop in a commercial A356 cast component that is subjected to a standard commercial heat treating cycle. In order to verify the accuracy of the software predictions, the predictions were compared to their measured counterparts, where dimensional changes and distortion were measured with a coordinate measuring machine, and residual stresses were measured with x-ray diffraction.
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Dewhirst, Brian A. "Optimization of the heat treatment of semi solid processed A356 aluminum alloy." Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-111705-111503/.
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Thesis (M.S.)--Worcester Polytechnic Institute.Keywords: microstructure; casting; Fluid Bed; Quality Index; Aluminum; A356; heat treatment; SSM; Semi Solid Metal Includes bibliographical references. (p.105-106)
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Yao, Lu. "Experimental investigation and numerical modeling of microporosity formation in aluminum alloy A356." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/36372.
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Microporosity refers to small voids in the material in the size range from a few to hundreds of micrometers. These small voids can reduce the fatigue performance of the cast components. In the foundry industry, numerous efforts have been made to predict and control microporosity formation.
The present work studies the formation of microporosity in A356 (Al-7wt%Si-0.3wt%Mg) aluminum alloy castings. The focus is on prediction of pore size distribution, which is a crucial factor in fatigue analysis. This requires precise experimental characterization of pore size and simulation of both nucleation and growth kinetics of the pores.
In the initial stage of this work, microporosity formed in directionally solidified tapered cylindrical A356 casting samples were analyzed using high resolution X-ray microtomography (XMT). The results showed that increasing the cooling rate and degassing time yields lower microporosity within the microstructure.
These microporosity data were later used to validate a numerical model that simulates microporosity formation in A356 castings. In this model, the nucleation site distribution of the pores is a Gaussian function of hydrogen supersaturation in the melt. The pore growth is a hydrogen-diffusion controlled process. With the model it is possible to evaluate the relative contributions of hydrogen content, cooling rate and nucleation sites to microporosity formation, and to quantify the pore nucleation kinetics at given casting conditions.
Furthermore, this model was applied to study the effect of oxide inclusions on pore nucleation kinetics. Castings were prepared under different casting conditions aimed at manipulating the tendency to form and entrain oxides in the melt. Two alloy variants of A356 were tested in which the main difference was Sr content. By fitting the experimental results with the pore formation model, an estimate of the pore nucleation site distribution has been made. It is shown increasing the tendency to form oxide films increases both the number and potency of nucleation sites. Based on the model prediction, Sr-modification impacts both the pore nucleation and pore growth kinetics.
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Madgwick, Alexander. "Creep and damage in an A359 aluminium alloy/SiC metal matrix composite." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620311.
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Lyons, Jed S. "Microstructural influences on fracture toughness in A357 cast aluminum alloys." Thesis, Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/16689.
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Chen, Chia-Jung. "OPTIMIZATION OF MECHANICAL PROPERTIES IN A356 VIA SIMULATION AND PERMANENT MOLD TEST-BARS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1386184784.
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Furlan, Tarita Shiraishi. "Influência do teor de estrôncio na modificação da liga A356." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-31032008-095727/.
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O objetivo deste trabalho foi o de otimizar a adição de estrôncio em liga A356 visando obter as melhores propriedades mecânicas de ductilidade. Foram estudados diferentes níveis de adição de estrôncio em ligas A356 com dois níveis de fósforo residual. Além disto, foi estudado o efeito de adições crescentes de magnésio na morfologia do silício em liga Al-7%Si modificada. Para a realização deste estudo, foram produzidos corpos de prova de tração segundo ASTM B108 com velocidade de resfriamento de 8°C/s. Os corpos de prova foram endurecidos por precipitação via tratamento térmico e tracionados. Além de uma avaliação quantitativa das propriedades mecânicas, amostras de todas as condições passaram por uma avaliação metalográfica qualitativa. Foi feito também ataque profundo para observação das morfologias das partículas de silício em microscópio eletrônico. O efeito da adição crescente de estrôncio na liga A356 em um intervalo de 0 a 256 ppm de estrôncio foi o de aumento do alongamento até teores de 50 a 60 ppm, seguido de uma diminuição do mesmo até 256 ppm. O teste de adição crescente de estrôncio foi repetido para uma liga A356 com teor residual de fósforo de aproximadamente 10 ppm. A curva de alongamento segue o mesmo formato da curva levantada para amostras que não continham fósforo, embora tenha sido encontrada uma sensível queda nos valores de alongamento na presença de fósforo. A presença de magnésio em ligas Al-Si modificadas por estrôncio foi responsável por uma mudança na morfologia de crescimento das partículas de silício nas regiões de contornos de células eutéticas, além do aparecimento de partículas intermetálicas nesta mesma região. Deste trabalho, concluiu-se que as melhores propriedades mecânicas de ductilidade foram obtidas para a adição de estrôncio de 50 a 60 ppm.This work has, as its main objective, the optimization of the strontium addition in A356 alloy, in order to obtain the best ductility results. The addition of several different strontium amounts in alloys containing two phosphorous amounts was studied. Besides, the effect of increasing magnesium content on the morphology of the silicon particles of Al-7%Si modified alloy was also studied. Test bars were produced from ASTM B108 cooled at a rate of 8°C/s. The samples were heat treated and then tested. The mechanical properties were evaluated and the microstructures were analyzed. The silicon morphology was observed in deep etched samples at SEM. Strontium additions of 0 to 256 ppm increased the elongation up to 50-60 ppm. Above 75 ppm, the addition of strontium caused the elongation to decrease up to 256 ppm. The same test was reproduced for an alloy containing approximately 10 ppm P and, although the best results were achieved at strontium additions of 50-60 ppm, the elongation results were clearly lower. The presence of magnesium in Al-7%Si modified alloys was responsible for a change in the growth morphology of the silicon particles, especially near grain boundaries, and also for the formation of intermetallic particles in those areas. From this work, it was possible to conclude that the best ductility properties are achieved for strontium additions of 50-60 ppm.
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Bogdanoff, Toni, and Jimmy Dahlström. "The influence of copper on an Al-Si-Mg alloy (A356) - Microstructure and mechanical properties." Thesis, Jönköping University, JTH, Mechanical Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-9480.
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Aluminum alloys are widely used in many manufacturing areas due to good castability, lightness and mechanical properties. The purpose of this research is to investigate copper’s influence on an Al-Si-Mg alloy (A356). Copper in the range of 0.6 – 1.6 wt. % has been used in an A356 aluminum based alloy. In this work a simulation of three different casting processes, sand-, die- and high pressure die-casting has been employed with the help of gradient solidification equipment. The microstructure of the samples has been studied by optical and scanning electron microscopy. Materials in both as-cast and heat treated states have been investigated through tensile test bars to get the mechanical properties of the different conditions.
Questions that have been subjected to answer are what influence does copper have on the plastic deformation and on fracture behavior and whether there is a relationship between the content of copper and increased porosity or not; and in that case explore this relationship between the amount of copper and the mechanical behaviour.
It has been analyzed that a peak of mechanical properties is obtained with a content about 1.6 wt. % copper. The increment of copper seems to have a remarkable impact on the mechanical properties and especially after the aging process showing a large raise on the ultimate tensile strength and yield strength.
Relationship between the copper content and increased porosity could not be found.
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Simpson, Ronald James. "The use of chills as a means of influencing solidification in lost foam cast aluminum alloy A356." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ28662.pdf.
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Hinton, Kimberly D. "Extended heat treatment effects on the fracture toughness of cast aluminum alloy A357." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/17361.
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Cardoso, Roberto. "Estudo sobre a incidência das porosidades e sua identificação em uma liga de alumínio A356." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-14012008-115212/.
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Este trabalho procurou identificar o defeito que ocorria no teste de estanqueidade de uma peça e apresentar a correlação entre o nível de porosidade encontrado no produto fundido com a liga de alumínio A356 e os processos de fusão e de manutenção sob temperaturas controladas, o teor de hidrogênio, o sistema de enchimento e de alimentação, obedecendo ao princípio de solidificação direcional e o posicionamento do modelo em relação à linha de divisão. Foram efetuadas algumas experiências com diferentes tempos de introdução de nitrogênio para a purificação do metal, com a inversão do modelo em relação ao plano de partição do molde, com a modificação das dimensões do sistema de enchimento, com a substituição dos massalotes laterais por outros com luvas exotérmicas e utilizando-se resfriadores. Tentou-se verificar os benefícios que os filtros cerâmicos proporcionam aos fundidos, principalmente quanto à diminuição do nível de porosidade, menor turbulência e maior capacidade de reter as inclusões e parte dos filmes de óxidos. Para comprová-los, propôs-se a fundição de peças, em moldes confeccionados pelo processo de areia à verde, com diferentes tipos de filtros cerâmicos nos canais de distribuição. As amostras foram analisadas no Laboratório Metalográfico do Departamento de Engenharia Metalúrgica e de Materiais da Escola Politécnica da Universidade de São Paulo e no Laboratório de Metalurgia e de Materiais Cerâmicos do Instituto de Pesquisas Tecnológicas de São Paulo. Após a análise dos resultados em microscópio óptico, microscópio eletrônico de varredura e em espectrômetro por emissão de energia observou-se que o problema está relacionado principalmente com a alimentação e a solidificação direcional e não somente com o teor de hidrogênio.The objective of this work is to study the type of defect identified during the pressure tightness test of aluminum parts and to establish a relationship between porosity level of an A356 aluminum alloy and the production processes, hydrogen level, feeding system, and directional solidification. Different nitrogen blowing times, inversion of the mould pattern, relative to the partition line, changing of the feeding system dimensions, replacement of the lateral feeding by exothermic gloves and the use of chills where tested. Ceramic filters were also tested, in order to evaluate their influence on the formation of porosities and on the porosity level, through a decrease of turbulence and an increase in the capacity of retaining non-metallic inclusions and part of the oxide films. Casting was performed by the green sand process using different ceramic filters. The obtained parts were metallographicaly analyzed through optical and scanning electronic microscopy using also EDS analysis. The results showed that porosity is related with the feeding conditions and directional solidification besides the hydrogen content of the alloys.
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Silva, Cássia Cavalcanti [UNESP]. "Efeito de inoculantes para refino de grão e modificador de eutético na curva de resfriamento da liga A356 e da liga A356 reciclada." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/141999.
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A liga AA 356 é uma liga Al-Si amplamente utilizada tanto na indústria automobilística como na aeronáutica. Para melhorar suas propriedades mecânicas, são usados inoculantes para o refino de grão e para modificação eutética. Os componentes solidificados em moldes metálicos, que são mais eficientes na extração de calor, em geral, têm propriedades mecânicas superiores àqueles solidificados em moldes de areia que apresentam uma menor taxa de extração de calor. A curva de resfriamento que é uma curva da temperatura em função do tempo obtida da extremidade de um termopar localizado no centro do molde e conectado a um sistema de aquisição de dados é uma ferramenta que permite avaliar tanto o refino de grão quanto a modificação eutética. Essa ferramenta permite observar também a formação de fases intermetálicas, e é influenciada por fatores como a taxa de resfriamento. A primeira derivada da curva de resfriamento que representa a taxa de resfriamento é parte da ferramenta, pois melhora a precisão dos dados obtidos com a curva de resfriamento. Para o desenvolvimento desse trabalho foram preparados lingotes variando-se o material do molde (areia e aço), o teor de modificador de eutético e a adição de refinador de grão, ambos na forma de ligas-mãe (ante-liga) Al-10Sr e Al-5Ti-1B, respectivamente. Os valores para traçar as curvas de resfriamento foram obtidos monitorando a temperatura do metal desde o vazamento até sua completa solidificação e posterior resfriamento. Amostras do material foram preparadas para metalografia e obtidas imagens de macroestrutura e microestrutura. Da microestrutura foram obtidas as imagens com o ataque químico convencional e o ataque químico profundo; foram realizadas medidas de fração de porosidade por área, por técnica de microscopia, além de medidas de dureza Vickers e Brinell. Os resultados confirmam que a técnica da análise térmica da curva de resfriamento é uma excelente ferramenta, pois além de fornecer as temperaturas solidus e liquidus, as temperaturas de transformações de fases e informações sobre a eficácia do refino de grão e modificação eutética, pode ser utilizada na avaliação da presença de impurezas e na identificação de fases presentes nas ligas, tanto da liga primária quanto da liga reciclada.
The alloy AA 356 is an Al-Si alloy widely used in the automotive and aeronautics industry. To improve the mechanical properties of this alloy inoculants are used to grain refine and eutectic modification. The solidified components in metal mold, with a higher heat extraction rate, generally have mechanical properties superior to those solidified in sand mold with a lower heat extraction rate. The cooling curve is a curve of temperature versus time obtained in the end of a thermocouple located in the center of the mold and connected to a data acquisition system. It is a tool to evaluate both the grain refinement as the eutectic modification. This tool also can also be used to observe the formation of intermetallic phases, and is influenced by factors such as the cooling rate. The first derivative of the curve representing the cooling rate is part of the tool because it improves the accuracy of the data obtained from the curve. For the development of this work ingots were prepared varying the mold material (sand and steel), the content of eutectic modifier and the grain refiner addition , both in the form of master alloys Al-10Sr and Al-5Ti-1B, respectively.The data for plotting the cooling curves were obtained experimentally during solidification; Samples of the material were prepared for metallography and macrostructure and microstructure images were obtained. Through microstructure images obtained with conventional etching and deep etching. Porosity fraction area was measured by microscopy technique and hardness measurements were performed by Vickers and Brinell metdhod. The results confirm that the thermal analysis of the cooling curve is an excellent tool because provides the solidus and liquidus temperatures and the phase transformations on the effectiveness of the grain refining and eutectic modification and it can be used to assess the presence of impurities in the phase identification, for both the primary alloy and the recycled alloy.
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Qi, Jiantao. "Trivalent chromium conversion coatings on Al and Al-Cu alloys." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/trivalent-chromium-conversion-coatings-on-al-and-alcu-alloys(138b7db5-0524-4bcc-a358-3d6bbc0d36d5).html.
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Trivalent chromium conversion coatings formed on Al and Al-Cu alloys has been investigated using high-resolution, analytical electron microscopy, atomic force microscopy, ion beam analysis, glow discharge optical emission spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, potentiodynamic polarization and electrochemical noise analysis. These coatings on the electropolished Al and sputtering-deposed Al consist of a chromium- and zirconium-rich outer layer and a thinner, aluminium-rich inner layer. Zirconium and chromium are presented in chemical states consistent with ZrO2, Cr(OH)3, Cr2(SO4)3, CrF3 and CrO3 or CrO42-. However, negligible amounts of hexavalent chromium species occurred in both coatings formed in de-aerated solution. On AA2024-T351 alloys, the coating above the second phase particles was thicker than that on the matrix due to the increased localized alkalinity. Moreover, the localized corrosion and copper enrichment of the matrix occurred at the coating base. The presence of copper resulted in a thinner coating at the matrix compared with superpure aluminium. An Fe(III)-containing D30 desmutter can effectively remove the protruded particles generated by alkaline etching. Moreover, a thinner oxide film on the D30-treated surface was evidenced to promote the coating initiation on the matrix. Further, the coating comprised the concentrated zirconium oxyfluorides and decreased contents of aluminium and copper. Coated alloys displayed a significantly enhanced corrosion protection, especially the cathoidc inhibition. In terms of coating post-treatments, the water immersion (40 ºC, pH 5) soon after conversion treatment revealed a simple but effective process to improve the fluoride enrichment in coatings and to enhance corrosion protection of freshly-developed coatings. Increasing concentration of solid-solution copper in sputtering-deposited alloys, in a range of 2, 24, 40 and 64 at.%Cu, significantly promotes the coating growth kinetics and an evident and a thicker corrosion layer by substrate dissolution was observed on Al-40 at.%Cu alloys. In addition, the relationship of copper-rich deposits with Cr(VI) transformation was demonstrated by Raman spectroscopy.
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Serrano, Munoz Itziar. "Influence of casting defects on the fatigue behaviour of an A357-T6 aerospace alloy." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0117/document.
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L’excellente coulabilité, les coûts de production relativement bas, et ratio poids/résistance mécanique élevé des alliages de fonderie Al-Si-Mg en font une des solutions les plus intéressantes dans le secteur automobile ainsi que dans le domaine aérospatial. Toutefois, il est bien connu que la durée de vie de ces composants moulés à grand nombre de cycles (105 < Nf < 107 cycles) est sévèrement réduite lorsque des défauts de fonderie (notamment pores et oxydes) sont débouchants et/ou subsurfaciques sont présents. Ces défauts concentrent les contraintes et peuvent considérablement réduire la période d’amorçage des fissures de fatigue en fonction de leur taille, forme et des caractéristiques microstructurales du matériau. Les défauts internes (à partir desquels les fissures peuvent amorcer et propager sans interaction avec l’air ambiant) ainsi que les défauts de surface (ceux qui sont placés à la surface et en contact direct avec l’air ambiant) vont également nuire la durée de vie des composants moulés. Toutefois, dans le cas des défauts internes, les coefficients de sécurité préconisés par les règles de conception ne font pas intervenir la distance de défaut par rapport à la surface. Le suivi de fissures de fatigue effectué à la surface d’éprouvettes macroscopiques de traction indique que la présence d’un défaut avec une taille supérieure à celle des fissures microstructuralement courtes (√A ≈ 500 μm, taille contrôlée par la SDAS) produit une remarquable réduction de la durée vie. En revanche, la durée de vie n’est pas affectée lorsqu’un défaut plus petit (√A ≈ 300 μm) est présent à la surface car l’amorçage et les premiers stades de propagation sont encore influencés par la SDAS. Les essais de fatigue en torsion pure montrent que la morphologie des surfaces de rupture est fortement influencée par le niveau de contrainte. De plus, le nombre de cycles à l’amorçage est réduit par rapport à la traction. Cet amorçage est multi-site et plusieurs fissures peuvent croitre simultanément au cours de la durée de vie d’une éprouvette, la rupture finale se produisant lors de la jonction de certaines de ces fissures. La propagation des fissures en torsion est largement influencée par la cristallographie locale et les retassures ne semblent pas être des sites de nucléation préférentiels. Les durées de vie odes échantillons macroscopiques contenant défauts artificiel internes (Øeq ≈ 2 mm) sont pratiquement similaires à celles obtenues avec un matériau de référence. L’amorçage et la propagation de fissures internes a été rarement observé lors des expériences de tomographie synchrotron. Dans les rares cas où de telles fissures ont pu être observées, le chemin de fissuration semble fortement influencé par la cristallographie alors que les fissures amorcées depuis la surface se propagent globalement en mode I. La vitesse de propagation des fissures internes est très inférieure à celle des fissures se propageant à partir de la surfaceThe excellent castability, relatively low production costs, and high strength to weight ratios make Al-Si-Mg cast alloys an attractive choice for use in cheaper and lighter engineering components, in both automotive and aerospace industries. However, it is well known that High Cycle Fatigue (HCF) lives (105 < Nf < 107 cycles) of cast components are severely reduced when casting defects (notably pores and oxides) are present at the free surface or subsurface. They act as stress raisers which can considerably reduce the crack incubation period depending on their size, shape and the microstructural features of the surrounding material. Internal casting defects are of special interest to this work. The application of safety coefficients considers that all casting defects present in a component have the same deleterious effect and no attention is paid, for example, to their distance to the free surface. In other words, internal defects (corresponding to the case where the depth of the defect allows crack nucleation and propagation to essentially occur without interaction with the air environment) are considered as damaging to fatigue life as surface defects (those placed at the free surface and in contact with the air environment). Surface crack monitoring performed on uniaxial fatigue specimens indicates that the presence of a surface microshrinkage exceeding the size of microstructurally small cracks (√A ≈ 500 μm, controlled by the SDAS) readily nucleates a fatigue cracks producing steady crack propagation and remarkable reduction in the expected fatigue life. A smaller surface defect (√A ≈ 300 μm) nucleated a crack that did not reduced the expected fatigue life as in this case early stages of propagation are still nfluenced by the SDAS. Pure torsional cycling reveals that the morphology of fracture surfaces is highly influenced by the stress level. In general, torsional fatigue behaviour is described by having reduced (with respect to uniaxial testing) and multisite crack nucleation periods. Several dominant cracks can evolve simultaneously and the final failure occurs by the linkage of some of those cracks. Crack propagation is controlled by the crystallography and pores do not appear to be preferential nucleation sites. S-N curves show that macroscopic specimens containing Øeq ≈ 2 mm internal artificial defect produce similar fatigue lives to those obtained with a defect-free material. Internal crack nucleation was rarely observed during synchrotron tomography experiments; instead the fatal cracks initiated from much smaller surface defects. Tomographic images show that, in the case of internal propagation, crystallographic paths are formed while surface cracks propagate in mode I. The crack growth rate of internal cracks is much smaller than that of cracks propagating from the free surface
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Silva, Valdinei Ferreira da. "Comportamento da liga de alumínio A356-T6 fundida e tixoextrudada sob fadiga isotérmica e termomecânica." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-25072012-143154/.
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Gradientes térmicos induzidos no interior de componentes sujeitos a variações de temperatura durante o período de funcionamento podem provocar a ocorrência de tensões e deformações internas. A repetição destes ciclos térmicos pode causar a nucleação e a propagação de trincas por um processo denominado fadiga termomecânica. Este trabalho apresenta um estudo sobre o comportamento da liga de alumínio A356-T6, processada nas condições fundida e tixoextrudada, sob fadiga isotérmica e termomecânica. Foram realizados ensaios de fadiga de baixo ciclo isotérmica para as temperaturas de 120 e 280°C, e ensaios de fadiga termomecânica em-fase e fora-de-fase para a faixa de temperatura de 120 a 280°C. O material tixoextrudado apresentou melhor desempenho em fadiga nas condições isotérmica e anisotérmica (termomecânica) devido a uma microestrutura globular com menor nível de porosidade.Thermal gradients induced in components during service under temperature changes can cause internal stresses and strains. This cyclic thermal behavior can cause crack nucleation and propagation under a process denominated thermomechanical fatigue. Permanent mold casting and tixoextruded A356-T6 aluminum alloy behavior under isothermal and thermomechanical fatigue was study in this work. Isothermal low cycle fatigue tests were performed in temperatures of 120 and 280°C. In-phase and out-of-phase thermomechanical fatigue tests were carried out in temperature range from 120 to 280°C. The tixoextruded material presented better isothermal and thermomechanical fatigue performance due to a globular microstructure and lower porosity level.
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Lados, Diana Aida. "Fatigue crack growth mechanisms in Al-Si-Mg alloys." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0204104-125758.
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Thesis (Ph. D.)--Worcester Polytechnic Institute.Keywords: Microstructure; Elastic-Plastic Fracture Mechanics; Crack closure; A356; J-integral; Conventionally cast and SSM Al-Si-Mg alloys; Residual stress; Heat treatment; Fatigue crack growth mechanisms; Threshold stress intensity factor; Plastic zone; Paris law; Fracture toughness; Roughness. Includes bibliographical references.
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Haskel, Tatiane. "Efeito do tratamento térmico de solubilização na microestrutura e nas propriedades mecânicas da liga de alumínio A356." Universidade do Estado de Santa Catarina, 2009. http://tede.udesc.br/handle/handle/1742.
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Previous issue date: 2009-07-23Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
This work examines the effects of solution heat treatment on the microstructure and mechanical properties of A356 aluminum alloy. Tensile bars were molten to tensile tests and solution treatment in several conditions of time and temperature were performed. The A356 alloy with different weight percentage of magnesium and with its respective as-casting specimens were also analysed to evaluate the heat treatment. To evaluate the results tensile tests, alloy hardness and matrix microhardness, and metallographic analysis and fractographs were performed. The microstructural analysis allowed to evaluate the evolution of microstructural transformation. Results changes were attained to alloy with less percentage of Mg (0,15wt. %). However, to the alloy with higher percentage of Mg (0,3wt. %) the results indicated increase in all properties analysed, increasing the time and the temperature of solution. Only to the temperature of 570°C, a property drop of ultimate tensile strength and elongation were observed. The best properties were obtained to 10 hours of the solution in 540°C, as a result of a better distribution and coalescence of the Si particles. The fractographs showed changes on the fracture mode in function of increase in the solution time and temperature, evidencing the increase of the ductility observed through mechanical tests. The kind of alloy fracture and the matrix fracture mode and Si particles were evidenced in fracture surfaces.
Este trabalho avalia os efeitos do tratamento térmico de solubilização sobre a microestrutura e as propriedades mecânicas da liga de alumínio A356. Foram fundidos corpos de prova para ensaios de tração e realizados tratamentos de solubilização em diversas condições de tempo e temperatura. A liga A356, com diferentes percentuais em peso de magnésio e com suas respectivas amostras brutas de fundição, também foram analisadas para avaliação dos efeitos do tratamento térmico. Para avaliação dos resultados foram realizados ensaios de resistência à tração, de dureza da liga e microdureza da matriz e, análises de metalografias e fractografias. As análises microestruturais permitiram avaliar a evolução da transformação microestrutural. Variações nos resultados foram obtidos, para liga com menor teor de Mg (0,15% em peso). Porém, para liga com maior teor de Mg (0,3% em peso) os resultados indicaram aumento em todas as propriedades analisadas, com o aumento do tempo como da temperatura de solubilização. Apenas para temperatura de 570°C uma queda nas propriedades de máxima resistência e alongamento foram observadas. As melhores propriedades foram obtidas com 10 horas de solubilização a 540°C, como resultado de uma melhor distribuição e coalescimento das partículas de Si. As fractografias mostraram alterações no modo de fratura, em função do incremento no tempo e na temperatura de solubilização, evidenciando o aumento de ductilidade observada através dos ensaios mecânicos. O tipo de fratura da liga, e o modo de fratura da matriz e das partículas de Si também foram evidenciados pelas superfícies de fratura.
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Singh, Shailesh Kumar. "Experimental and Numerical Investigation on Friction Welding of Thixocast A356 Aluminium Alloy." Thesis, 2013. http://etd.iisc.ernet.in/handle/2005/2847.
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The challenges of weight reduction and good strength in automotive industry have drawn considerable interest in thixocasting technologies. Joining of such components with conventional fusion welding creates voids, hot cracking, distortion in shape, and more importantly evolution of dendritic microstructure that ultimately would lead to inferior mechanical properties of the weld region. Thus, the purpose of making thixocast component is lost. The friction welding which is a solid state joining process can avoid defects associated with melting and solidification in a typical fusion weld and can be a promising alternative. This process produces a weld under compressive force at the contact of workpieces rotating or moving relative to one another to produce heat and plastically displacing material from the faying surfaces. Research on semisolid processing has its origin in the early 1970s. However, from the literature survey on semisolid processing it is clear that, till date, not much work has been done in field of joining of semisolid processed components. In the area of solid state welding, in particular, it is not at all explored. In view of this, the present work is focused on exploration of joining of Thixocast A356 Aluminium alloy component by friction welding and comparison of its performance with friction weld of conventionally cast sample of the same alloy. The study is carried out experimentally as well as numerically. Moreover, the material behaviour of thixocast component at elevated temperature in solid state is also described with the help of processing maps and constitutive modelling.
The hot workability of thixocast and conventionally cast A356 alloy is evaluated with the help of processing maps developed on the basis of the dynamic materials model approach using the flow stress data obtained from the isothermal compression test in wide range of temperature (300-500℃) and strain rates (0.001s-1-10s-1). The domains of the processing map are interpreted in terms of the associated microstructural mechanism. On comparing the flow stress at elevated temperature of thixocast and conventionally cast A356 alloy samples, it is observed that the flow stress of the latter showed higher value at different strain level, temperature and strain rates. This indicates that the flow property of the thixocast alloy sample is better than
that of the conventionally cast one (i.e. response to plastic flow is better for the former); while at room temperature thixocast sample has higher strength. Moreover to investigate the general nature of the influence of strain, strain rate and temperature on the compressive deformation characteristics of thixocast A356 and conventionally cast A356 aluminium alloy, a comprehensive model describing the relationship of the flow stress, strain rate and temperature of the alloys at elevated temperatures is proposed by hyperbolic-sine Arrhenius-type equation and Johnson-Cook model. The validity of descriptive results based on the proposed constitutive equation is also investigated and a comparison between two constitutive models is also made. In order to numerically model the friction welding process of a thixocast A356 aluminium alloy and conventionally cast alloy of same material using a finite element method (FEM), temperature dependent physical properties, mechanical properties as well as viscoplastic constitutive equations were used in the model. A two- dimensional axisymmetric finite element model has been developed. The modelling is based on a coupled thermomechanical approach. First, a nonlinear, transient two-dimensional heat transfer model is developed to determine the temperature fields. Later, the temperature fields are used as input for a nonlinear, two-dimensional structural model in order to predict the distortions and von Mises stress. The finite element models are parametrically built using APDL (ANSYS Parametric Design Language) provided by ANSYS. The validation of the model is carried out by comparing with the experiment. Once validated, the thermomechanical model was used to perform parametric studies in order to investigate effects of various process parameters on temperature and stress distribution in the workpieces. This helps in deciding the range of parameters for friction welding experiments in order to get good weld. Both thixocast and conventionally cast samples exhibited similar temperature distribution during the friction welding process, because of identical thermophysical properties. The magnitude of von Mises stress distribution during friction welding of thixocast A356 sample is found to be lower than that of the conventionally cast sample. It is because of their different constitutive behaviour at elevated temperature. Moreover, the developed FEM model can be successfully used to predict the residual stress at various locations for different set of parameters and geometry for friction welding of thixocast and conventionally cast A356 alloy. This helps in reducing time consuming and expensive experiments on residual stress measurement.
The chosen experiments based on Taguchi L27 orthogonal array were conducted on the friction welding machine which works on the principles of continuous drive-mechanism. The experimental specimens were machined from thixocast A356 aluminium alloy connecting rods as well as conventionally cast A356 aluminium alloy ingot in the form of cylindrical bars of dimensions 85mm length and 20mm diameter. The parameters used for welding were friction pressure, rpm, forge pressure, burn-off, and upset pressure. The effects of welding parameters on performance characteristics (i.e. tensile strength and weld efficiency) were evaluated. Taguchi method was applied to investigate the influence of each parameter on strength of joints and evaluate the combination of parameters that leads to the highest weld strength. Accordingly optimum process parameters was identified which helps in achieving the tensile strength of more than parent material. The optimized process parameters for friction welding of thixocast A356 aluminium alloy are rpm = 500, friction pressure = 60, upset time = 5, upset pressure = 100 and burn off = 5. The empirical relationships were also developed to predict the tensile strength. The developed relationship can be effectively used to predict the tensile strength of welded joint with a correlation coefficient of 0.86, which indicates the strong positive relationship between predicted and experimental data. Friction welding of thixocast A356 aluminium alloy helps to achieve very fine eutectic silicon particles of the order of 0.4 at the interface due to severe plastic deformation taking place during welding. Obtaining such fine eutectic silicon particles is difficult to be achieved within few seconds of processing by any other method. The hardness variation of friction welded thixocast alloy shows higher value as compared to that of a conventionally cast sample in the heat affected zone, which indicates better weld strength of the former. This was also confirmed by the tensile strength studied and fatigue test. This indicates that weldability of cast alloys will get improved if the microstructure is modified to globular type.
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Jacobs, H. "The fatigue and tensile properties of A356 aluminium alloy wheels in various post cast conditions." Thesis, 2008. http://hdl.handle.net/10210/1754.
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M.Ing.This dissertation investigates the fatigue and monotonic tensile properties of cast aluminium alloy wheels in various post cast conditions. It was found that monotonic tensile properties could be used in the original universal slopes method of Manson to predict the fatigue properties as a conservative first approximation for A356 cast aluminium alloy wheels. Using finite element analysis and the predicted fatigue properties the fatigue life of A356 aluminium alloy wheels could be determined. Further work is required on the surface effect of paint on the wheel and residual stress on the surface of the wheel.
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Sudarshan, *. "Processing And Characterization Of Fly Ash Particle Reinforced A356 Al Composites." Thesis, 2004. http://etd.iisc.ernet.in/handle/2005/1295.
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Yang, Yaw-Sheng, and 楊耀昇. "The Semi-Solid Processing of the A356 aluminium-silicon alloy :the effects of processing parameters on the microstructure viscosity and thixotropy property." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/02070306950831217734.
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Pramod, kumar *. "Experimental Investigation Of Rheocasting Using Linear Electromagnetic Stirring." Thesis, 2008. http://hdl.handle.net/2005/1059.
Full textAbstract:
In several applications of casting, dendritic microstructure is not desirable as it results in poor mechanical properties. Enhancing fluid flow in the mushy zone by stirring is one of the means to suppress this dendritic growth. Strong fluid flow detaches the dendrites formed at the solid-liquid interface and carries them into the mould to form slurry. When this slurry solidifies, the microstructure is characterized by globular, non-dendritic primary phase particles, separated and enclosed by a near-eutectic lower-melting secondary phase. This property represents a great potential for further processing in semisolid forming (SSF) by various techniques such as pressure die casting and forging. Among all currently available methods, linear electromagnetic (EM) stirring is considered as one of the most suitable routes for large scale production of semisolid feed stock. One of the biggest advantages of EM stirring is that the stirring intensity and direction can be modulated externally and in a non-intrusive manner. With this viewpoint, the primary objective of the present research is to investigate rheocasting using linear electromagnetic stirring.
A systematic development of a linear electromagnetic stirrer (LEMS) is the subject of the first part of the thesis. The LEMS consists of a set of six primary coils displaced in space. These coils are excited by a three-phase power supply to produce an axially travelling magnetic field. The metal to be stirred is placed in the annular space of the stirrer. The travelling field induces secondary current in the molten metal. The current and magnetic fields interact to generate a net mechanical force in the metal, commonly termed as the Lorentz force. The molten metal is stirred under the influence of this force. Two prototype stirrers, one for low melting alloys and the other for aluminium alloys are developed. The stirrers are characterized by measuring forces on low melting point alloy and on solid aluminum cylinders placed inside the annular space of the stirrer. As an outcome of these tests, a non-intrusive method of detecting stirring of liquid metal is developed.
The development of a rheocasting mould for the LEMS forms the second part of the work presented in the thesis. The mould design and cooling arrangement are such that solidification in the mould is primarily unidirectional. Heat from the solidifying metal is extracted at the bottom of the mould, so that the axisymmetric EM stirring effectively shears the dendrites formed at the solid-liquid interface. The outer surface of the mould is cooled with water or air exiting from 64 jets, each of 4 mm diameter. Such an arrangement provides a high heat transfer coefficient and a wide range of cooling rate in the metal ranging from 0.01 to 10 K/s. Temperature is measured at various depths in the solidifying melt and at other key locations in the mould to assess the various heat transfer mechanisms.
The results from the rheocasting experiments using the above mould and LEMS are presented in the third and final part of the thesis. Such studies are required for understanding the solidification process in presence of electromagnetic stirring and for highlighting the important issues connecting solidification, fluid flow, dendrite fragmentation and the resulting microstructure. A series of experiments are performed with A356 (Al-7Si-0.3Mg) alloy. Experiments are conducted with various combinations of operating parameters, and the resulting microstructures and cooling curves at various locations are examined. The key process parameters are stirring current, cooling rate, pouring temperature, and stirring current frequency. The parametric studies also include the case without EM stirring in which liquid aluminium is poured into the rheocast mould without powering the LEMS.
It is found that stirring at high currents produces non-dendritic microstructures at all locations of the billet. For lower currents, however, dendritic microstructures are observed in regions outside the zone of active stirring. Stirring also enhances heat loss from the exposed top surface, leading to solid front advancement from the top as well. Without EM stirring, microstructures are found to be dendritic everywhere. The percentage of primary α-Al phase and its number density are found to increase with stirring intensity. With a decrease in cooling rate with air as the coolant, the average grain size of primary α-Al phase increases. Excitation frequency is found to be an important parameter, with lower frequencies generating a more uniform force field distribution, and higher frequencies enhancing induction heating. At higher frequencies, the effect of higher induction heating results in the formation of larger and coarser primary phase grains. This phenomenon has led to the development of a one-step process for rheocasting and heat treatment of billets.
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Tsai, Wei-Xiang, and 蔡維翔. "Direct Squeeze Cast A356 Aluminum alloy." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/93951993802795546405.
Full textAbstract:
碩士國立中央大學
機械工程研究所
95
Effects of particle/pore counts, oxide film, and alloy compositions on hardness and mechanical properties of squeezed cast Al-7Si-0.4Mg alloys at different process parameters ( pouring temperature and squeeze pressure ) were investigated in this study. Experimental results show that: (1) Increase both magnesium and silicon content slightly increase hardness and mechanical properties of squeezed Al-7Si-0.4Mg alloy. (2) Particle counts trapped in squeezed Al-7Si-0.4Mg show low fraction of eutectic silicon. (3) Pore counts effects the measured hardness of squeezed Al-7Si-0.4Mg alloy. (4) Reliability on UTS is highest (Weibull parameter for squeezed Al-6Si-0.3Mg alloy is 53.7) when pouring temperature is 685℃, mold temperature remains 180-200℃ and squeeze pressure keeps 120MPa.
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Vo, Phuong. "Mathematical modeling of microporosity in A356 aluminum alloy." Thesis, 2002. http://hdl.handle.net/2429/12295.
Full textAbstract:
Die cast aluminum wheels are one of the most difficult automotive castings to produce
because of stringent cast surface and internal quality requirements. As part of a
collaborative research agreement between researchers at the University of British
Columbia and Canadian Autoparts Toyota Inc., work has been underway to predict heat
transport and porosity formation in die cast A356 wheels. Preliminary work has focused
on assessing a number of criteria functions previously proposed in the literature. Model
results in the form of temperature and criteria function predictions are compared with
experimentally measured temperature and porosity data obtained from a directionally
chilled A356 aluminum alloy solidified under conditions resembling those found in an
industrial die-casting operation. The results suggest that the Niyama function is best
suited to qualitatively predict porosity of the four criteria functions examined. However,
all criteria functions, including the Niyama, do not appear to be well suited to predict the
amount of porosity quantitatively as they fail to include the effect of varying hydrogen
and inclusion content. A 2-D axisymmetric mathematical model incorporating flow
through the interdendritic network and the thermodynamics of hydrogen solubility has
been developed. This model has been successfully applied to the prediction of the
amount of porosity in a series of test castings with varying hydrogen content.
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Chih-Wei, Huang, and 黃志瑋. "The study of semisolid processes of A356 Aluminum Alloy and aluminum alloy containing scandium." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/48218287090536699804.
Full textAbstract:
碩士元智大學
機械工程學系
93
This study investigated the variations of casting aluminum alloy A356 and wrought aluminum alloy M9 (Al-7.81Zn-2.36Mg-1.9Cu-0.11Zr-0.06Sc wt.％) by semisolid process. The spherical grains were formed by casting and extrusion. The solid fraction and the size of spherical grain were observed. The purpose of this study was size of spherical grain smaller than 50μm. The fine spherical grains of A356 and M9 aluminum alloy were gained by strain-induced melt activation (SIMA). The region of liquid of M9 aluminum alloy was not conspicuous, but the region of liquid of A356 aluminum alloy is conspicuous. The long grains were produced in extrusion by the semisolid heat treatment. The long grains conduced to decreased flow. The macro-segregation produced by the long grain cracked in the die-casting. The long grain does not suit with semisolid process.
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Chen, Wen-Chi, and 陳文吉. "Effects of Preaging on the Mechanical Properties and Precipitation rate of A356 and A357 Casting Aluminum Alloys." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/77617575280097011633.
Full textAbstract:
碩士國立中央大學
機械工程學系
84
The effect of preaging on the A356 and A357 casting alloys were studied bymeans of differential scanning calorimetry, conductivity meter, hardness and tensile test.The results show that nature aging would retard the subsequent artificial aging and reduce the peak aging strength; the damage of natureaging on A357 alloy is more than A356 alloy.The long of preaging at 90C would reduce the effect of nature aging and increase the peak aging strength of A356and A357 alloys.Higther artificial aging temperature could reduce the effect of nature agingand the time to peak aging.
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Lin, Chia-Sin, and 林家新. "The directional solidification study of A356 aluminum alloy and Al-Si eutectic alloy." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/j2n4ue.
Full textAbstract:
碩士國立中山大學
材料與光電科學學系研究所
102
Directional solidification technique applied to investigate the dendrite alloy segregation and the phase identification in multiple phases co-precipitation. Because the large size dendrite could form in directional solidification which would provide large scale to investigate the dendrite segregation from dendrite center region to edge region. For the eutectic type alloys, several phases formed together and have the difficulty to identify these fine phases. These alloys could solidify under slower directional solidification condition and form larger phase. A356 aluminum alloy and add 1 wt.%Mn alloy were applied in this study. The influence of thermal gradient, extruding rate and chemical composition to microstructure were investigated. In A356 aluminum alloy and it add 1wt.% Mn we found the Al dendrite is larger than nature cooling then it is good to carry out quantitative analysis, we also can find the Al dendrite grow paralleled with heat in A356 but not in A356 with 1wt.% Mn, and the precipitate will convert to fibrous from plates when the extruding rate reduced. When A356 alloy addition 1 wt.% Mn the Al5FeSi IMC would convert to Al15(Fe,Mn)3Si2. We also take Al-Si and Al-Si-Cu eutectic system, due to the current temperature parameter, the microstructure is not as expected. Because the lower thermal gradient caused the lower cooling rate, and generated ageing behavior. Thus the change of extruding rate is not affecting the microstructure.
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Hou, Martin, and 侯國南. "Computer Simulation of Porosity Distribution in A356 Aluminum Alloy Castings." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/78399297072992308577.
Full textAbstract:
碩士國立成功大學
材料科學(工程)學系
85
This study aimed at comparing computer simulation with experimentalmeasurement of the porosity distribution in A356.2 aluminum alloy castingsof dimensions 25 dia. X 150 L mm cast in a steel mold. In the experiment, hydrogen content was precisely detected by an advancedAlscan hydrogen quantitative analyzer, and thermal measurements were done toobtain thermal variables in the casting. The porosity in the casting measuredby Archimedes principle was compared with that predicted by thermal variables. Computer simulation was proceeded by: (1) construction of geometry andanalysis models per Patran3, (2) simulation of filling and solidificationprocesses per ProCAST, (3) calculation of porosity distribution via differentparameters, and (4) displaying of analysis results per Patran3 and Excel. In this study, the commercial solidification software and aluminum porosityqualitative/quantitative model have been integrated . And the nine porosityparameters were compared : (1) solidification time, (2) thermal gradient,(3) solidus velocity, (4) solidification rate, (5) thermal parameter ( G/tf ) ,(6) thermal parameter G/R0.5 , (7) thermal parameter (LEE) , (8) parameter ( p ) ,and (9)quantitative model. The results showed that the nine parameters are not all congruent. Thismight be due to the different casting conditions from which the parameterswere derived. From comparing the different parameters and the experimentresults, it was found that the quantitative model showed the best accuracyin porosity prediction.
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陳錫貴. "Squeeze Casting of A356 Aluminum Alloy-304 Stainless Steel Clad Material." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/91467289445571125328.
Full textAbstract:
碩士國立臺灣科技大學
工程技術研究所
80
The effects of processing parameters, dipping temperature. dipping time and external applied pressure, on the bonding strength of A356 aluminum allov and 304 stainless steel cladding material were studied. Specimens were produced by squeeze casting method and by gravity casting method using 304 stainless steel as insert. Metallurgical observation, SEM/EDAX, tensile test and hardness mealsurement were used to analvze the bonding strength of the this cladding material. Experimental results indicated that the thickness of diffusion laver increased with increasing hot-dipping temperature, hot-dipping time and external applied pressure. The highest bonding strength is 43.35MPa obtained by squeeze casting with 850℃ dipping temperature, 60sec dipping time, 80MPa external applied pressure. The main effect of external applied pressure. The main effect of external applied pressure is to increasing the bonding strength of diffusion layer instead of increasing the thickness of diffusion layer.
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YU, SHENG CHUN, and 余聲均. "Effect of additional element on mechanical properties of A356 aluminum alloy." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/20649193398864605100.
Full textAbstract:
碩士國立中央大學
機械工程學系
84
This reserach was conducted in order to study the effect of additional element on mechanical propertiesof A356 aluminum alloy. Furthermore , the effect ofthe additional element on strength , elongation , micrstructure will be investigated.It is observed that the addition of Cu and Mn resultedin increase the tensile strength. The reason is that when the Cu and Mn in A356 aluminum alloy will decrease the precipitational tempeture of metastable phase. The additional Sn And Zn on A356 aluminum alloys can not increase the mechanical properties ofA356 aluminum alloy. The additional Cu element has the best elogation.The additional Zn element has low effect of A356 aluminum alloy.
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LIN, H. Y., and 林宏宇. "The CAE Analyses of Riser Feedability for A356 Aluminum Alloy Casting." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/55554938667993403938.
Full textAbstract:
碩士大葉大學
機電自動化研究所碩士班
93
The study of riser feeding is mainly focus on steel and cast iron,but their feeding principles are not suitable for A356 aluminium Alloy.This research used the CAE software-AFSolid system to modify Caine's riser feeding rule and to measure the feeding distance of riser for A356 aluminium alloy.The flowing velocity of computer simulation result reveals the different effect of various gating ratio for gating system.The empirical model of feeding distances of risers for A356 aluminium alloy casting was also calculated by regression analysis method.In addition,this study also investigates the effects of thermal parameters on the soundness of A356 alloys casting by criteria hot spot,thermal gradient,cooling rate and solidification time.The practical castings poured by CO2 sand mold and X-ray examination were performed to understand the validity of CAE results. The results of study show that the gating system with 1:4:4 gating ratio had a stable melt flow for A356 aluminium alloy.From the prediction of defects simulated by those criteria stated above,the hot spot will be in the riser if the casting can get adeguate feeding.The greater thermal gradient and cooling rate can promote the feeding efficiency of castings and prevent the shrinkage of castings.As the solidification time of risers is longer than that of castings,the feeding will be sound.In addition,the difference between the Caine's riser feeding rule and the results of simulation shows that the sound range of riser's feeding should be modified.Through the examination of X-ray for inspecting the practical A356 step-castings and plate-castings also shows that the shrinkage positions are correspondent to the computer simulation.
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SHEU, GUANG-LIANG, and 許光良. "Study on the Filling Behavior of the EPC A356 Aluminum Alloy." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/57768550610921251749.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
88
This study explores the mold-filling behavior of the A356 melt cast in the EPC molds with a two-layer gating system design. Influences of gating system dimensions and some selected processing parameters, including the pouring temperature, the pattern position (the inclined angle), the coating thickness and the amount of glue applied, were investigated. The experimental results indicate that the tendency of the molten Al to flow into the upper layer is decreased almost linearly with increasing the upper layer sprue height, while is increased also linearly with increasing the lower layer sprue height. If the lower layer sprue height were too long, the temperature drop of the melt become excessive, resulting in substantial reduction in the filling velocity. Also, increasing the sprue cross sectional area promotes the filling of the upper layer, but the starting filling time of both upper and lower layers are delayed. In addition, there exits proper value of the sprue and ingate areas for the optium melt filling velocity, either too big or too small of both areas causes undesirable filling velocities. The gravitational effect on mold filling velocity starts to become significant as the inclined angle of the pattern with respect to the horizontal direction is greater than 45O. The filling velocities in both upper and lower layers being affected more. In addition, raising the pouring temperature increases the filling velocity significantly, and also promotes the filling of the upper layer in the early stage of the mold filling. Further, the effect of coating thickness on mold filling is not significant due to the fact that the coating used in this study is a high permeable type. Finally, as more glue was applied, the metal filling velocity is reduced proportionally. In this study, an equation has been derived which can estimate the amount of the A356 melt flowing into the upper layer before the lower layer starts to filling.
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Fang, Ren Yu, and 方仁宇. "Study of Friction between Aluminum Alloy-A356 and Epoxy Resin- moglice." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/04599093739376100107.
Full textAbstract:
碩士國立臺灣大學
機械工程學系
85
Based on the working condition of machine tools, this study performs anexperiment of friction on epoxy resin - moglice sliding against aluminum alloy- A356 at different velocities, loads and surface roughness. The coefficient of friction of A356-moglice is 0.25 under dry sliding contact condition while thatis 0.15 under boundary lubrication. The results are applied on small-sizedmilling machine guideways to prove their frictional performance.
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WU, DE-HUA, and 吳德樺. "Squeeze casting of A356 aluminum-alloy-medium carbon steel clad material." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/95921071380840158729.
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康振雄. "Transient heat transfer analysis of squeeze casting for A356 aluminum alloy." Thesis, 1988. http://ndltd.ncl.edu.tw/handle/15211412080059401898.
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Cheng, Ming Cheng, and 鄭明城. "Quantitative Modeling of Porosity Formation in an A356 Aluminum Alloy Cylindrical Casting." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/85521338188288086859.
Full textAbstract:
碩士國立成功大學
材料科學(工程)學系
84
Producing aluminum alloy castings by low pressure casting has the advantages of semi-automatic production,labor saving, improving casting quality and yieldratio.Hence,low pressure casting is a trend of aluminum castings'''' development.According to Sigworth''''s study , 1/2 to 3/4 of casting rejects are due to theporosity defect. Therefore , the main purpose of this study is to explore thefeeding behave of aluminum low pressure casting. SKD61 permanent mold was used to cast 25φ×150L mm sample.In the experiment, mold temperature, hydrogen content in the melt, and gauge pressure from 0to 1kg/cm^2 were changed to simulate the low pressure casting.Hydrogen contentwas precisely detected by an advanced Alscan hydrogen quantitative analyzer. Moreover , thermal measurements were used to obtain thermal variables in thecasting. The result of the change of mold temperature indicated that increasing moldtemperature can increase the solidification time , eliminate negative thermalgradient and solidus velocity , promote directional solidification , and lower the porosity content in the center of casting. Increasing mold temperature ,however , adversely increased the porosity content in the casting near the feeder by virtue of an increase of solidification time. The result of simulated low pressure casting indicated that, except free end , increasing gauge pressure lowered the solidification time , directionalsolidification in the center of casting,thermal gradient,increased the solidusvelocity, and the cooling rate . The effect of gauge pressure on the porositycontent could be explained by the pressure drop . The pressure drop had a maximum in the center of casting （ >0.58atm ）when using a gauge pressure of 0.5 atm. Therefore,if gauge pressure did not greater than the maximum pressuredrop as mention above , the quality of casting in the center would be poorerthan that of the gravity casting . But the porosity of casting in the centercould be reduced when using 1.0 atm gauge pressure. The pressure drop was small in the feeder and solidification time was much larger than the time ofengaging pressure on the feeder. Therefore , with increasing gauge pressure ,the porosity of casting near the feeder could be reduced . With increasing initial hydrogen content in the melt , the porosity contentof casting could be reduced . A change of initial hydrogen content moved the porosity content level . The porosity content was directly proportional to1/P^★ , and the slope was a function of hydrogen content.