Submitted by Maria Suzana Diniz (msuzanad@hotmail.com) on 2015-11-12T13:09:59Z No. of bitstreams: 1 Arquivototal.pdf: 4725274 bytes, checksum: 00ba23047c493bdc8d085328b0239721 (MD5) / Made available in DSpace on 2015-11-12T13:10:01Z (GMT). No. of bitstreams: 1 Arquivototal.pdf: 4725274 bytes, checksum: 00ba23047c493bdc8d085328b0239721 (MD5) Previous issue date: 2015-01-05 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The squeeze casting process is a casting process in which the cast metal in the liquid state is solidified under pressure in a metal mold closed off by a punch. In general components manufactured by squeeze casting have fine grained, high surface finish and almost free of porosity, may be the same of different sizes and shapes, the mechanical properties are enhanced significantly in comparison with the traditional method of casting and, in addition, parts manufactured by squeeze casting possess superior weldability and are able to heat treatment, and finally compared to the common casting parts manufactured by squeeze casting are formed in one operation with a lower energy consumption. The objective of this study is to analyze the influence of pressure as well as the zinc content of the alloys in the secondary dendrite spacing, the hardness and tensile strength limit, and correlate the microstructures with the mechanical properties and process parameters. For this purpose we used the mass compositions Al-Zn 1% Al-Zn 3% and Al-Zn 5% solidified with the squeeze casting process using the pressure 50 MPa, 100 MPa and 150 MPa, and the pressing time of 5 seconds. It is observed that the increase in pressure causes a reduction in dendrite spacing until 100 MPa, pressure variations from this point up to 150 MPa causes a increase in the secondary dendrite spacing, was also observed that the Vickers hardness and the tensile strength limit have a relationship with the secondary dendrite spacing. / O processo squeeze casting é um processo de fundição, no qual o metal vazado no estado liquido, é solidificado sob pressão dentro de um molde metálico fechado por um punção. Em geral componentes fabricadas por squeeze casting possuem granulação fina, excelente acabamento de superfície e quase livre de porosidade, os mesmo podem ser de diferentes tamanhos e formatos, as propriedades mecânicas são aumentadas significantemente, em comparação ao método tradicional de fundição e, além disso, peças fabricadas por squeeze casting possuem soldabilidade superior e são aptas a tratamentos térmicos, e finalmente em comparação com a fundição comum peças fabricadas por squeeze casting são formadas em uma só operação com um menor consumo de energia. O objetivo deste trabalho é analisar a influencia da pressão assim como do teor de zinco das ligas no espaçamento dendrítico secundário, na microdureza e no limite de resistência à tração, e correlacionar as microestruturas com as propriedades mecânicas e com os parâmetros de processo. Para tal foram utilizadas as composições Al-1%Zn , Al-3%Zn e Al-5%Zn em massa, solidificadas com o processo squeeze casting usando as pressões 0 MPa, 50 MPa, 100 MPa e 150 MPa, com o tempo de prensagem de 5 segundos. Observa-se que o aumento da pressão causa uma diminuição no espaçamento dendrítico até a pressão 100MPa, a partir deste ponto variações até 150 MPa causam aumento no espaçamento dendrítico secundário, observou-se também que a microdureza vickers assim como o limite de resistência à tração apresentam uma relação com o espaçamento dendrítico secundário.

Submitted by PPG Engenharia e Tecnologia de Materiais (engenharia.pg.materiais@pucrs.br) on 2017-10-10T12:03:59Z No. of bitstreams: 1 Tese_Bernardo_2017_R18_3_Versao_PGETEMA.pdf: 6957919 bytes, checksum: e8811a19bda3fe37ea9ed6f6247594ac (MD5) / Approved for entry into archive by Caroline Xavier (caroline.xavier@pucrs.br) on 2017-10-10T13:43:30Z (GMT) No. of bitstreams: 1 Tese_Bernardo_2017_R18_3_Versao_PGETEMA.pdf: 6957919 bytes, checksum: e8811a19bda3fe37ea9ed6f6247594ac (MD5) / Made available in DSpace on 2017-10-10T13:48:22Z (GMT). No. of bitstreams: 1 Tese_Bernardo_2017_R18_3_Versao_PGETEMA.pdf: 6957919 bytes, checksum: e8811a19bda3fe37ea9ed6f6247594ac (MD5) Previous issue date: 2017-08-31 / CAPES/PROSUP / The objective of the present work is to develop two modified ternary Al-Zn-Mg alloys, with Zn content about 5wt% and 8wt%, and to evaluate the precipitation hardening (solutioning and artificial ageing ? T6) as a function of solidification conditions. The 752 (Al-5%Zn-2%Mg) and 782 (Al-8%Zn-2%Mg) alloys were obtained to analyze the influence of Zn content, as well as the relationship between solidification conditions, precipitation hardening, and mechanical properties before and after heat treatments. Unidirectional vertical upward solidification was performed in a metallic mold cooled by water in the bottom and instrumented using thermocouples to obtain the ingots. Samples extracted from ingots were metallography characterized by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and the mechanical properties were determined by hardness, microhardness, tensile and wear testing. The results showed that the increase of 3% of zinc in the chemical composition improved the hardness of 44%, the superficial wear of 27.7% and the tensile strength of 31.5% (in T6 condition). When comparing the results against data from some similar wrought alloys, it is concluded that the as-cast and heat treated 782 alloy can replace those, according to design specifications. / O objetivo do presente trabalho foi desenvolver duas ligas tern?rias fundidas modificadas de Al-Zn-Mg, com varia??o de 5% e 8% em Zn (em massa), e investigar o endurecimento por precipita??o (solubiliza??o e envelhecimento artificial - T6) em fun??o das condi??es de solidifica??o. Foram produzidas as ligas 752 (Al-5%Zn-2%Mg) e 782 (Al-8%Zn-2%Mg) para analisar, al?m da influ?ncia do teor de zinco, a correla??o entre as condi??es de solidifica??o, o endurecimento por precipita??o e as propriedades mec?nicas iniciais e finais. Para obten??o dos lingotes, a solidifica??o unidirecional vertical ascendente foi realizada em molde met?lico resfriado com ?gua na base e instrumentado com termopares. Amostras foram caracterizadas por an?lises metalogr?ficas em microscopia ?ptica (MO), microscopia eletr?nica de varredura (MEV), espectroscopia de energia dispersiva (EDS), e ensaios mec?nicos para determina??o das propriedades mec?nicas como dureza, microdureza, tra??o e desgaste, antes e ap?s os tratamentos t?rmicos. Os resultados mostraram que o aumento em 3% de zinco na composi??o qu?mica melhorou a dureza em 44,4%, o desgaste superficial em 27,7% e a resist?ncia ? tra??o em 31,5% (em condi??o T6). Comparando estes resultados com dados de algumas ligas conformadas similares, conclui-se que a Liga 782, fundida e tratada termicamente, pode substituir as ligas conformadas comerciais com adi??o de cobre.

The deformation mechanism of an ultrafine grained (UFG) Al-Zn alloy has been studied. In this work, Al-15wt%Zn alloy was processed by equal channel angular extrusion (ECAE) route A at 100oC to achieve UFG structure. The deformation mechanism was studied by performing tensile test with various strain rates. Scanning electron microscopy and transmission electron microscopy were used to investigate the microstructure evolution in Al-15wt%Zn alloy with increasing ECAE passes. The observation indicated that the super saturated Al-Zn alloy would decompose and precipitate Zn particles during ECAE process. Increasing ECAE passes, the aluminum grain size was reduced, but the size of Zn particles was increased. However, the net effect of increasing ECAE passes is softening of this Al-Zn alloy. The tensile properties of the UFG Al-Zn alloy can be summarized as follows. (1)The UFG Al-Zn alloy possesses higher tensile strength and elongation as compared to commercial purity Al (AA1050). (2)The strain rate sensitivity of the UFG Al-Zn alloy increases significantly with increasing number of ECAE pass, which might be related to the refined aluminum grain size. After processed by 4-16 ECAE passes, the activation volume of the UFG Al-Zn alloy falls in the range of 25 b3~40 b3, which remains nearly constant value with increasing tensile strain. It is suggested that the controlling mechanism responsible for the tensile deformation of the UFG Al-Zn alloy might be related to a grain boundary mediated mechanism. (3)With increasing ECAE passes, the total tensile elongation of the UFG Al-Zn alloy increases but the uniform elongation show little change. This indicates that the increase in total elongation is mainly due to the contribution from an enhanced post-uniform elongation (PUE). It is suggested that the enhanced PUE might be related to the increase in strain rate sensitivity, which is resulted from the refinement of grain size. More detailed studies are needed to understand the deformation mechanism.

No description available.

No description available.

Mechanical properties of thermal spray deposited coatings are highly influenced by their microstructural characteristics. The objective of this investigation is to evaluate the mechanical properties of thermally sprayed coatings consisted of aluminum and zinc based on the coating microstructure, using an image based computational scheme. Microstructural images of coating samples were subjected to image-based finite element analysis and the results were validated by experimental tests and analytical models. Comparison of the experimental data with FEA was used to explain the microstructural basis of the mechanical characteristics of Al-Zn coatings and the differences between two methods of thermal spray techniques. It was concluded that the cold spraying technique produces higher-quality coatings with less porosity and higher hardness compared to wire arc deposition. An isotropic behavior was observed in the cold sprayed coating. Finally, the electrochemical tests showed that the coating with a higher amount of zinc had better anti-corrosion properties.

Nous étudions la fragilisation par l'hydrogène de l'alliage d'aluminium 7108. Une technique expérimentale spécifique a été développée : Un pré-chargement en hydrogène des échantillons, à travers un dépôt de nickel de quelques dizaines de microns, qui empêche la dissolution du substrat d'aluminium, est utilisé. Il permet la comparaison de la résistance à la fragilisation de différentes microstructures modèles. Nous étudions l'effet du traitement thermique et de la précipitation sur la sensibilité à l'hydrogène pour des vitesses de déformation macroscopiques imposées variables. Différents modes de rupture sont observés ainsi que des transitions entre eux. Au moyen de simulations numériques à l'échelle mésoscopique, l'effet de taille des précipités intergranulaires pré-fragilisés sur la ténacité des joints de grains est estimé, en utilisant un modèle de zone cohésive. Nous analysons la compétition entre la diffusion de l'hydrogène vers la pointe de la fissure et la vitesse de fissuration par un couplage mécanique - diffusion basé sur la diffusion de l'hydrogène assistée par la contrainte hydrostatique. Une vitesse critique au-delà de laquelle l'hydrogène ne peut plus suivre la fissure, est mise en évidence. L'influence de la microstructure du joint de grains sur cette vitesse est analysée. La valeur est comparée à une estimation des vitesses de propagation expérimentales obtenues pour différentes vitesses de déformation macroscopiques. Nous analysons l'effet du piégeage de l'hydrogène par les précipités intergranulaires et la désorption sur la répartition de l'hydrogène le long du joint de grains en imposant un flux au niveau de l'interface précipités - matrice. / We study the hydrogen embrittlement of the 7108 aluminum alloy. A specific experimental technique was developed : A hydrogen pre-charging, through few tens of microns of deposit of nickel, which prevents the dissolution of the aluminum substrate is used. It allows a comparison of the resistance to embrittlement of different model microstructures. We study the effect of heat treatment and intergranular precipitation on the susceptibility to hydrogen embrittlement for several macroscopic strain rates. Different failure modes and transitions between them are observed. Through numerical simulations, at the mesoscopic scale, the effect of the size of pre-weakened intergranular precipitates on the grain boundary toughness is estimated using a cohesive zone model. We further analyze the competition between the hydrogen diffusion toward the crack tip and crack velocity. For this purpose, a mechanical – diffusion coupling based on the hydrogen diffusion assisted by hydrostatic stress is elaborated. A critical crack velocity, beyond which hydrogen can no longer follow the crack, is highlighted. The influence of the grain boundary microstructure on this critical crack velocity is evaluated and its value is compared with an estimate of velocities obtained for different experimental macroscopic strain rates. We analyze the effect of hydrogen trapping by intergranular precipitates and hydrogen desorption by imposing a flux at the precipitates – matrix interfaces.

Le soudage des alliages Al-Zn-Mg est de plus en plus utilisé dans l'industrie du transport. Les variations brutales de température induites par le soudage à l'arc provoquent des modifications importantes de la microstructure dans la zone dite affectée thermiquement.<br />Cette étude porte sur l'évolution de la précipitation suite à ce procédé de l'alliage 7108.50 présentant différentes microstructures initiales. Une caractérisation fine des précipités durcissants dans la zone affectée thermiquement a été menée par SAXS, MET et DSC juste après soudage et après traitements thermiques post-soudage. Afin de mieux cerner les mécanismes influençant la précipitation au cours de ce procédé anisotherme, des traitements thermiques contrôlés, de type réversion ou rampes de montée en température, ont également été étudiés.<br />Un modèle basé sur l'évolution d'une distribution en taille de particules a été développé afin de prédire l'état de précipitation après divers traitements thermiques, dont le soudage.

Nous étudions la fragilisation par l'hydrogène de l'alliage d'aluminium 7108. Une technique expérimentale spécifique a été développée : Un pré-chargement en hydrogène des échantillons, à travers un dépôt de nickel de quelques dizaines de microns, qui empêche la dissolution du substrat d'aluminium, est utilisé. Il permet la comparaison de la résistance à la fragilisation de différentes microstructures modèles. Nous étudions l'effet du traitement thermique et de la précipitation sur la sensibilité à l'hydrogène pour des vitesses de déformation macroscopiques imposées variables. Différents modes de rupture sont observés ainsi que des transitions entre eux. Au moyen de simulations numériques à l'échelle mésoscopique, l'effet de taille des précipités intergranulaires pré-fragilisés sur la ténacité des joints de grains est estimé, en utilisant un modèle de zone cohésive. Nous analysons la compétition entre la diffusion de l'hydrogène vers la pointe de la fissure et la vitesse de fissuration par un couplage mécanique - diffusion basé sur la diffusion de l'hydrogène assistée par la contrainte hydrostatique. Une vitesse critique au-delà de laquelle l'hydrogène ne peut plus suivre la fissure, est mise en évidence. L'influence de la microstructure du joint de grains sur cette vitesse est analysée. La valeur est comparée à une estimation des vitesses de propagation expérimentales obtenues pour différentes vitesses de déformation macroscopiques. Nous analysons l'effet du piégeage de l'hydrogène par les précipités intergranulaires et la désorption sur la répartition de l'hydrogène le long du joint de grains en imposant un flux au niveau de l'interface précipités - matrice.

Les alliages d'aluminium de la série 7xxx sont des alliages à durcissement structural, principalement utilisés dans des applications aéronautiques en raison de leurs propriétés mécaniques spécifiques élevées. Le composant principal de leur résistance mécanique est leur microstructure de précipitation, obtenue par le biais de traitements thermomécaniques complexes. Ceux-ci induisent cependant des contraintes internes à longue distance, susceptibles de générer des distorsions sévères dans les pièces aéronautiques. Certains traitements thermomécaniques comme le grenaillage (shot peening), le formage laser (laser forming) et le formage revenu (age-forming), des procédés respectivement purement mécanique, purement thermique et thermomécanique, permettent de réduire les distorsions de pièces usinées. Ils modifient cependant la microstructure, et, par conséquent, les propriétés mécaniques. La présente étude, portant sur les couplages entre ces traitements thermomécaniques, la microstructure et les propriétés mécaniques d'un alliage 7xxx, comprend un travail de caractérisation expérimentale et de modélisation à base physique. L'effet de la précipitation sur l'écrouissage du matériau est ainsi examiné, et un modèle d'écrouissage destiné à être implémenté dans un modèle éléments finis de simulation du grenaillage est proposé. L'étude du formage laser aboutit quant à elle à un modèle prédictif de l'état de précipitation et des propriétés mécaniques locales induits par ce procédé. La dernière partie est consacrée à l'étude de l'effet du formage revenu – procédé combinant déformation plastique et traitement thermique simultanés – sur la précipitation.