This study focuses on hot and warm forming properties of aluminum alloy AA5182 sheet, with attention toward warm forming, by using gas pressure to form sheet material. A temperature range of 300°C to 450°C and a pressure range of 690 kPa (100 psi) to 2410 kPa (350 psi) were used in a test matrix of twenty one different test conditions for gas-pressure forming of a sheet into hemispherical dome in a gas-pressure bulge test. Multiple sets of tensile data were used to develop a material model that predicts the dome height and shape of an axisymmetric bulge specimen at any given time during forming. In simulations of the forming process, 17 simulations of the total 21 experimental conditions showed good agreement with the experimentally measured dome heights throughout forming tests. The four cases that did not show good agreement between simulation and experiment are a result of strain-hardening in the material during forming. Strain hardening was not significant in tension testing of specimens and was not accounted for in the material model, which considered only strain rates slower than for these experimental bulge testing. This demonstrates an effect which must be considered in future simulations to predict forming approaching warm conditions. Two experimental bulge specimens were cross-sectioned post forming and grain sizes were measured to determine if grain growth occurred during the forming process. Experimental bulge specimens show no grain growth during the forming process. The tensile specimens from which the material model data were taken were measured to determine if plastic anisotropy was a possible issue. All specimens measured were proved to have deformed nearly isotropically. The results of this study show that predicting warm and hot forming of aluminum alloy AA5182 using gas pressure is possible, but that a more complex material model will be required for accurate predictions of warm forming. This is a very important step toward making hot and warm forming commercially viable mass production techniques. / text

The retrogression-reaging (RRA) and hot forming behavior of AA7075 were studied. AA7075 is a high-strength alloy used in applications where weight is of particular importance, such as in automobiles. Like many of the high-strength aluminum alloys, AA7075 requires elevated temperature forming to achieve ductility comparable to steels at room temperature. Since AA7075 is a precipitation hardening alloy, heat treatments during forming and production need to be closely controlled to limit any loss of strength due to changes in the microstructure. Two new forming concepts are introduced to explore the feasibility of forming AA7075 in manners compatible with current automotive manufacturing processes. They are RRA forming and solution forming. These concepts seek to improve upon the room-temperature formability of AA7075-T6 and incorporate the paint-bake cycle (PBC) into the heat treatment process. The PBC is a mandatory heat treatment used to cure the paint applied to automobiles during production. Currently, the PBC is conducted at 180 °C for 30 minutes. RRA behavior was studied with molten salt bath treatments between 200 and 350 °C. The PBC was used in lieu of the standard 24 hour reaging treatment conducted at 121 °C. It was determined that retrogression treating below 250 °C was acceptable for RRA forming, with retrogressing at 200 °C producing the hardest material after reaging by the PBC. The formability of AA7075-T6 during RRA forming was evaluated by tensile testing at 200 and 225 °C. Ductility of AA7075-T6 at RRA forming temperatures was double compared to those produced at room temperature. RRA forming was demonstrated to achieve this improved ductility and a final material hardness after the PBC of only slightly less than the peak-aged condition. In addition, solution forming behavior was studied at 480 °C. Solution forming can increase ductility compared to RRA forming, but it requires aging at 121 °C prior to the PBC to produce peak-aged hardness. / text

Les travaux de cette thèse s'insèrent dans le cadre de l'étude de défauts détectés par contrôle ultrason dans des pièces forgées en alliage d'aluminium destinées à l'industrie aéronautique.Cette étude a été menée sur deux pièces produites par Aubert&Duval en alliage d'aluminium 7050 fourni par Constellium. Ces pièces ont été sélectionnées sur base d'une étude statistique de l'occurrence des défauts sur cinq années de production industrielle. L'une présente un taux de rebut important du fait de ces défauts, l'autre un taux de rebut quasiment nul, bien qu'elles soient produites avec le même matériau.L'étude de l'origine des défauts a été construite autour de deux axes de recherche:• Axe thermomécanique : formation des défauts pendant la mise en forme par endommagement ductile à chaud.• Axe matériau : caractérisation des défauts préexistants dans le matériau après son élaboration et non refermés pendant la mise en forme.L'axe thermomécanique est basé sur la simulation numérique des gammes de mise en forme des pièces industrielles à l'aide du logiciel Forge® 2009. Le deuxième axe est articulé autour de la caractérisation de l'état de porosité dans un matériau modèle présentant une teneur en hydrogène élevée induisant un taux de porosité plus important que le matériau sain utilisé industriellement. De petits lopins de ce matériau modèle ont été soumis à une campagne de compression alternée simulant le forgeage industriel. La campagne de compression a été conçue par simulation numérique afin de reproduire les conditions thermomécaniques industrielles. Deux techniques de caractérisation complémentaires ont été mises en œuvre pour suivre l'évolution de la porosité : détection indirecte par contrôle ultrason à haute résolution spatiale et observations directes par microscopie électronique à balayage. Une méthode d'analyse quantitative des signaux ultrasonores a été mise au point pour ce travail.La comparaison par simulation numérique du procédé de matriçage des deux pièces industrielles étudiées a permis d'écarter l'hypothèse de la création des défauts par endommagement ductile à chaud. Lors du matriçage, la matière est soumise à des chargements globalement compressifs, et le risque d'endommagement est par conséquent très faible. De plus, comme observé lors de la caractérisation des défauts industriels, les défauts présentent un fond lisse, similaire au fond lisse observé sur les rares porosités présentes dans le matériau industriel à l'état brut d'élaboration. Le même type de fond lisse caractérise également les porosités présentes dans le matériau modèle. Cette observation favorise l'hypothèse de défauts provenant d'un défaut préexistant dans le matériau initial (en l'occurrence à partir d'une porosité). Cette hypothèse est par ailleurs cohérente avec le comportement des porosités lors de la simulation du forgeage sur petits lopins du matériau modèle.Les résultats de cette étude montrent en effet que les porosités ont tendance à s'aplatir et à se refermer pendant la déformation plastique à chaud, sans forcément cicatriser. Les faciès de rupture d'échantillons soumis à de fortes déformations cumulées et ne donnant plus de réponse ultrasonore significative continuent en effet de présenter de petites plages à fond lisse qui témoignent d'une cicatrisation incomplète. Le traitement thermique semble en outre favoriser la réouverture des porosités non cicatrisées (zones lisses) pendant la déformation et leur élargissement (zones ductiles). / The thesis project aims to study the origin of defects detected in 7XXX aluminium alloy components for aeronautical applications.This work was conducted on two different components (A and B) produced by Aubert&Duval using 7050 aluminium alloy ingots produced by Constellium. The choice of these two components is based on a five year industrial production statistical analysis. Component A has a much higher defect rate compared to component B, even though they are produced from the same ingots.This work was conducted according to two research axis:• Thermo-mechanical axis : defects occurred during the material forming as a result of ductile hot damage• Material axis: defects resulted from a pre-existent defect in the raw material that was not closed during forming.The thermo-mechanical axis is based on numerical simulations of the component's forming processes using the Forge® 2009 software. The material axis is based on the experimental characterization of porosity in a model material with high hydrogen content and thus a higher pore density than the industrial material. Small samples of the model material were experimentally forged using an alternating compression test that was designed and developed from the industrial forging process. Theses samples were characterized to describe pore evolution during hot deformation, by the combination of two characterization techniques: High Resolution Ultrasound Control (HRUS) and Scanning Electron Microscope (SEM) observations on 2D sections and fracture surfaces. An ultrasound signal processing technique was also developed in order to quantitatively compare two different deformation states using ultrasound control.The results of the numerical simulation of A and B component stamping process showed that the detected defects could not occur by ductile hot damage. Indeed, the stamping process is purely compressive and damage risks are thus very low. Moreover, the defect experimental characterization showed the presence of smooth surface areas very similar to the surface aspect of the rare observed porosity in the raw material. The same smooth aspect characterized the porosity observed in the model material. These results lead to the hypothesis that the detected defects could occur from a pre-existent defect (porosity more precisely) in the raw material. This hypothesis is consistent with the pore behaviour during the experimental hot forging of the model material.The hot forging experiment conducted on the model material, showed that pores tend to flatten as plastic strain increases. SEM observations on rupture surfaces from the highest plastic strain showed the presence of small smooth aspect areas. These areas confirm that some pores are not completely healed during deformation even though the correspondent ultrasound signal is very low. During heat treatment, unhealed pores after deformation seem to be reopened (smooth aspect surface areas) and expanded (ductile areas).

This thesis was developed in the frame of a Brazil-France cooperation agreement between the École des Mines d\'Albi-Carmaux and the Polytechnic School of Engineering of the University of Sao Paulo (EPUSP). It aims to contribute to the study of the mechanical behaviour of Ti6Al4V alloys especially in terms of superplastic forming. The general objective of this research is to develop non-conventional forming processes for new titanium alloys applied to aerospace components Therefore, in accordance of the equipment\'s available in the two groups, the work will be conducted either at the Ecole des Mines d\'Albi-Carmaux and either at EPUSP. This thesis aims to answer questions such as what are the implications in relation to the microstructural and mechanical behaviour of these alloys during superplastic and hot forming in order to establish a behaviour law for these alloys based on titanium. This requires a good knowledge of the properties of materials used in the superplastic and hot forming domain to control the parameters governing the phenomenon of superplasticity or high temperature plasticity. For this, a testing strategy and characterization methodology of those new titanium alloys was developed. The tests include high temperature uniaxial tensile tests on several Ti6Al4V alloys showing different initial grain sizes. Special focus was made on the microstructural evolution prior to testing (i.e. during specimen temperature increase and stabilization) and during testing. Testing range was chosen to cover the hot forming and superplastic deformation domain. Grain growth is depending on alloy initial microstructures but also on the duration of the test at testing temperature (static growth) and testing strain rate (dynamic growth). After testing microstructural evolutions of the alloys will be observed by optical micrograph or SEM and results are used to increase behaviour model accuracy. Advanced unified behaviour models where introduced in order to cover the whole strain rate and temperature range: kinematic hardening, strain rate sensitive and grain growth features are included in the model. In order to get validation of the behaviour model, it was introduced in ABAQUSR numerical simulation code and model predictions (especially macroscopic deformation and local grain growth) were compared, for one of the material investigated, to axisymmetric inflation forming tests of sheet metal parts, also known as bulge test. To obtain a simple control cycle, tests performed at IPT/LEL laboratory in San José Dos Campos in Brazil were operated with a constant strain rate. Results show a very good correlation with predictions and allows to conclude on an accuracy of the behaviour models of the titanium alloys in industrial forming conditions. / Esta tese desenvolvida dentro do acordo de cooperação internacional celebrado entre a Escola Politécnica da Universidade de São Paulo (EPUSP) e a École des Mines d\'Albi-Carmaux tem como tema principal a análise da influência da evolução microestrutural sobre o comportamento mecânico de chapa de liga de titânio - Ti-6Al- 4V sob condições superplásticas e trabalho a quente. O objetivo desta pesquisa é contribuir para o desenvolvimento de processos de conformação não convencional de chapas de ligas a base de titânio utilizadas na manufatura de componentes metálicos. Como objetivo específico, estabelecer uma correlação entre comportamento mecânico e a mudança microestrutural a partir de três tipos de ligas com diferentes tamanhos de grão iniciais (0.5, 3.0 e 4.9 ?m). Os testes foram realizados na faixa de temperatura de 700 a 950 °C combinados às taxas de deformação na faixa de 10-1 s-1 - 10-4 s-1. Para a metodologia, estabeleceu-se uma estratégia de ensaios mecânicos capaz de testar as hipóteses sobre o comportamento do material formuladas no início desta pesquisa. Em seguida, os ensaios mecânicos foram divididos em três partes. Na primeira, utilizou-se um simulador termomecânico modelo Gleeble 3800 para os ensaios a quente variando-se a taxa de deformação (??) entre 10-1 s-1 a 10-3 s-1 e temperaturas da ordem de 700 °C a 850 °C. Na segunda parte dos testes, priorizouse taxas de deformação mais lentas (10-2 s-1 - 10-4 s-1) e temperaturas mais elevadas (800 °C - 950 °C) objetivando atingir as deformações superplásticas do material, nesta etapa utilizou-se como equipamento uma máquina de tração modelo MTS 50kN com câmara de aquecimento acoplada. A terceira parte dos ensaios experimentais envolveu a conformação na condição superplástica por pressão hidrostática (Bulge test) realizadas no LEL-IPT de São José dos Campos. A partir da análise dos dados experimentais levantou-se os parâmetros introduzidos no modelo numérico de comportamento mecânico baseado na evolução da microestrutura da chapa testada permitindo a calibração do modelo numérico a partir das equações constituintes e finalmente introduzido no software de elementos finitos (ABAQUS 6.12) e construído a simulação numérica da conformação superplástica por pressão hidrostática. Os principais resultados indicaram uma forte correlação entre microestrutura inicial da conformação superplástica e a quente de onde se pode observar que tanto menor a microestrutura inicial maior será a quantidade do crescimento de grão. Os resultados da conformação superplástica de expansão multiaxial do domo hemisférico foram, então, comparados à simulação numérica permitindo confrontar os dados do modelo numérico do comportamento mecânico com a lei de comportamento estudada, o que possibilitou um melhor entendimento dos mecanismos da conformação plástica em condições de superplasticidade e também de trabalho a aquente do material.

The hot forming-quenching (HFQ) process has introduced grains and subgrain growth, accompanied with modification of the intermetallic particle distribution in AZ31 magnesium alloys. Each region of the HFQ component represents significant grain structure variation and surface conditions that contributed to the corrosion susceptibility. The homogeneous grain structure significantly ruled the corrosion propagation features by filiform-like corrosion. Immersion of AZ31 alloys in 3.5 wt.% NaCl indicated higher corrosion rate of HFQ TRC (corrosion rate: 10.129 mm/year), a factor of 10 times, higher than the rolled alloy (corrosion rate: 0.853 mm/year) and a factor of 2 times, higher than the corrosion rate of MCTRC alloy (corrosion rate: 5.956 mm/year). Much lower corrosion rate was indicated in the as-cast TRC and MCTRC alloys, compared to the alloys after HFQ process that revealed the contribution of network or continuous distribution of β-Mg17Al12 phase particles to reduce the corrosion driven in chloride solution. In contrast, discontinuous distribution of cathodic β-Mg17Al12 phase particles increases the corrosion rate of HFQ TRC alloy by promoting the cathodic reaction and intense filament propagation resembling the coarse interdendritic and grain boundaries attack. The presence of high population densities of cathodic Al8Mn5 particles in HFQ rolled AZ31B-H24 alloy significantly reduced the corrosion driven for intense corrosion attack on the rolled alloy. The surface preparation by mechanical grinding process induced MgO and Zn-enrichment layer, accompanied with near surface deformed layer that consisted of nanograins in the range size of 40 to 250 nm. The grinding process refined the surface by removing the cutting damage and marks that formed during the thermomechanical process and led to stable potential of the HFQ AZ31 alloys, in the range of -1.59 to -1.57 V, during open circuit potential (OCP) measurement. The surface regularity with grinding path causing the filament to propagate following the grinding direction. The as-received surface contained many cutting damages and deep scratch marks from the rolling and casting processes that could introduce many corrosion initiation sites. The absence of the grinding direction on the as-received surface could control intense corrosion susceptibility, due to the non-linear filament propagation. The surface irregularity on chromic acid cleaned surface of HFQ rolled AZ31B-H24 alloy also contributed to low corrosion potential of the rolled alloy during OCP and potentiodynamic polarization measurement.

Hot forming of boron steels is becoming increasingly popular in the automotive industry due to the demands for weight reduction and increased safety requirements for new vehicles. Hot formed components offer a significant increase in strength over conventional cold-formed steels, which has allowed for reductions in material thickness (and thus weight) while maintaining the same strength. Hot formed components are typically used in structural applications to improve the integrity of the vehicle’s cabin in the event of a collision. It has been suggested, however, that the crash performance of certain hot formed parts may be increased by locally tailoring their mechanical properties to improve their energy absorption. The final microstructure of a hot formed part is driven by the rate at which it is cooled within the tooling during the forming and quenching process. By controlling the cooling rate of the part, it is possible to control the final microstructure, and thus the final mechanical properties. This thesis outlines the experimental and numerical studies that were performed for the hot forming of a lab-scale B-pillar. A hot forming die set was developed which has both heating and cooling capabilities to control the local cooling rate of the blank as it is formed and quenched. The first aspect of this research is to produce a hot formed part which is representative of an industrial component, and then to numerically model the process to predict the final mechanical properties. The second aspect is to produce a hot formed part with tailored mechanical properties, such that there are regions of the part with very high strength (very hard) and other regions with increased ductility (softer). By tailoring the microstructure to meet the performance requirement of a hot formed part, it may be possible to optimize its crash behavior and also reduce the overall weight. Cartridge heaters were installed into sections of the tooling allowing it to reach a maximum temperature of 400°C. Cooling channels are used in other sections to maintain it at approximately room temperature. Experiments were performed on 1.2 mm Usibor® 1500P steel at heated die temperatures ranging from 25°C to 400°C. In the fully cooled region, the Vickers hardness of the blank was measured to be 450 – 475 HV, on average. As the temperature of the heated region was increased, a significant softening trend was observed in the areas of the blank that were in contact with the heated tool. The greatest levels of softening occurred in the 400°C heated die trial. Hardness measurements as low as 234 HV were recorded, which represents a reduction in hardness of 49% compared to the fully cooled trials. Numerical models of the experiments were developed using LS-DYNA and use of its advanced hot forming material model which allows for microstructure and hardness prediction within the final part. The numerical models have shown promising results in terms of predicting the hardness trends as the temperature of the die increases. Thermal expansion of the tooling resulted in local changes in the geometry of the tooling which proved to be problematic during the forming and quenching stages of the process. The expansion caused unexpected changes in the part-die contact, and the resulting microstructures were altered. These thermal expansion issues were addressed in the current work by shimming the tooling; however, in future work the tooling should be designed to account for this expansion at the desired operating temperature.

Hot forming of boron steels is becoming increasingly popular in the automotive industry due to the demands for weight reduction and increased safety requirements for new vehicles. Hot formed components offer a significant increase in strength over conventional cold-formed steels, which has allowed for reductions in material thickness (and thus weight) while maintaining the same strength. Hot formed components are typically used in structural applications to improve the integrity of the vehicle’s cabin in the event of a collision. It has been suggested, however, that the crash performance of certain hot formed parts may be increased by locally tailoring their mechanical properties to improve their energy absorption. The final microstructure of a hot formed part is driven by the rate at which it is cooled within the tooling during the forming and quenching process. By controlling the cooling rate of the part, it is possible to control the final microstructure, and thus the final mechanical properties. This thesis outlines the experimental and numerical studies that were performed for the hot forming of a lab-scale B-pillar. A hot forming die set was developed which has both heating and cooling capabilities to control the local cooling rate of the blank as it is formed and quenched. The first aspect of this research is to produce a hot formed part which is representative of an industrial component, and then to numerically model the process to predict the final mechanical properties. The second aspect is to produce a hot formed part with tailored mechanical properties, such that there are regions of the part with very high strength (very hard) and other regions with increased ductility (softer). By tailoring the microstructure to meet the performance requirement of a hot formed part, it may be possible to optimize its crash behavior and also reduce the overall weight. Cartridge heaters were installed into sections of the tooling allowing it to reach a maximum temperature of 400°C. Cooling channels are used in other sections to maintain it at approximately room temperature. Experiments were performed on 1.2 mm Usibor® 1500P steel at heated die temperatures ranging from 25°C to 400°C. In the fully cooled region, the Vickers hardness of the blank was measured to be 450 – 475 HV, on average. As the temperature of the heated region was increased, a significant softening trend was observed in the areas of the blank that were in contact with the heated tool. The greatest levels of softening occurred in the 400°C heated die trial. Hardness measurements as low as 234 HV were recorded, which represents a reduction in hardness of 49% compared to the fully cooled trials. Numerical models of the experiments were developed using LS-DYNA and use of its advanced hot forming material model which allows for microstructure and hardness prediction within the final part. The numerical models have shown promising results in terms of predicting the hardness trends as the temperature of the die increases. Thermal expansion of the tooling resulted in local changes in the geometry of the tooling which proved to be problematic during the forming and quenching stages of the process. The expansion caused unexpected changes in the part-die contact, and the resulting microstructures were altered. These thermal expansion issues were addressed in the current work by shimming the tooling; however, in future work the tooling should be designed to account for this expansion at the desired operating temperature.

This thesis was developed in the frame of a Brazil-France cooperation agreement between the École des Mines d\'Albi-Carmaux and the Polytechnic School of Engineering of the University of Sao Paulo (EPUSP). It aims to contribute to the study of the mechanical behaviour of Ti6Al4V alloys especially in terms of superplastic forming. The general objective of this research is to develop non-conventional forming processes for new titanium alloys applied to aerospace components Therefore, in accordance of the equipment\'s available in the two groups, the work will be conducted either at the Ecole des Mines d\'Albi-Carmaux and either at EPUSP. This thesis aims to answer questions such as what are the implications in relation to the microstructural and mechanical behaviour of these alloys during superplastic and hot forming in order to establish a behaviour law for these alloys based on titanium. This requires a good knowledge of the properties of materials used in the superplastic and hot forming domain to control the parameters governing the phenomenon of superplasticity or high temperature plasticity. For this, a testing strategy and characterization methodology of those new titanium alloys was developed. The tests include high temperature uniaxial tensile tests on several Ti6Al4V alloys showing different initial grain sizes. Special focus was made on the microstructural evolution prior to testing (i.e. during specimen temperature increase and stabilization) and during testing. Testing range was chosen to cover the hot forming and superplastic deformation domain. Grain growth is depending on alloy initial microstructures but also on the duration of the test at testing temperature (static growth) and testing strain rate (dynamic growth). After testing microstructural evolutions of the alloys will be observed by optical micrograph or SEM and results are used to increase behaviour model accuracy. Advanced unified behaviour models where introduced in order to cover the whole strain rate and temperature range: kinematic hardening, strain rate sensitive and grain growth features are included in the model. In order to get validation of the behaviour model, it was introduced in ABAQUSR numerical simulation code and model predictions (especially macroscopic deformation and local grain growth) were compared, for one of the material investigated, to axisymmetric inflation forming tests of sheet metal parts, also known as bulge test. To obtain a simple control cycle, tests performed at IPT/LEL laboratory in San José Dos Campos in Brazil were operated with a constant strain rate. Results show a very good correlation with predictions and allows to conclude on an accuracy of the behaviour models of the titanium alloys in industrial forming conditions. / Esta tese desenvolvida dentro do acordo de cooperação internacional celebrado entre a Escola Politécnica da Universidade de São Paulo (EPUSP) e a École des Mines d\'Albi-Carmaux tem como tema principal a análise da influência da evolução microestrutural sobre o comportamento mecânico de chapa de liga de titânio - Ti-6Al- 4V sob condições superplásticas e trabalho a quente. O objetivo desta pesquisa é contribuir para o desenvolvimento de processos de conformação não convencional de chapas de ligas a base de titânio utilizadas na manufatura de componentes metálicos. Como objetivo específico, estabelecer uma correlação entre comportamento mecânico e a mudança microestrutural a partir de três tipos de ligas com diferentes tamanhos de grão iniciais (0.5, 3.0 e 4.9 ?m). Os testes foram realizados na faixa de temperatura de 700 a 950 °C combinados às taxas de deformação na faixa de 10-1 s-1 - 10-4 s-1. Para a metodologia, estabeleceu-se uma estratégia de ensaios mecânicos capaz de testar as hipóteses sobre o comportamento do material formuladas no início desta pesquisa. Em seguida, os ensaios mecânicos foram divididos em três partes. Na primeira, utilizou-se um simulador termomecânico modelo Gleeble 3800 para os ensaios a quente variando-se a taxa de deformação (??) entre 10-1 s-1 a 10-3 s-1 e temperaturas da ordem de 700 °C a 850 °C. Na segunda parte dos testes, priorizouse taxas de deformação mais lentas (10-2 s-1 - 10-4 s-1) e temperaturas mais elevadas (800 °C - 950 °C) objetivando atingir as deformações superplásticas do material, nesta etapa utilizou-se como equipamento uma máquina de tração modelo MTS 50kN com câmara de aquecimento acoplada. A terceira parte dos ensaios experimentais envolveu a conformação na condição superplástica por pressão hidrostática (Bulge test) realizadas no LEL-IPT de São José dos Campos. A partir da análise dos dados experimentais levantou-se os parâmetros introduzidos no modelo numérico de comportamento mecânico baseado na evolução da microestrutura da chapa testada permitindo a calibração do modelo numérico a partir das equações constituintes e finalmente introduzido no software de elementos finitos (ABAQUS 6.12) e construído a simulação numérica da conformação superplástica por pressão hidrostática. Os principais resultados indicaram uma forte correlação entre microestrutura inicial da conformação superplástica e a quente de onde se pode observar que tanto menor a microestrutura inicial maior será a quantidade do crescimento de grão. Os resultados da conformação superplástica de expansão multiaxial do domo hemisférico foram, então, comparados à simulação numérica permitindo confrontar os dados do modelo numérico do comportamento mecânico com a lei de comportamento estudada, o que possibilitou um melhor entendimento dos mecanismos da conformação plástica em condições de superplasticidade e também de trabalho a aquente do material.

In modern society, car manufactures are actively pursuing vehicle light weighting under both stricter government regulations due to environmental concerns and consumers’ demand for better fuel economy. Under such circumstances, OEMs are using more parts using aluminum alloys to replace parts made with steel. New forming processes are being developed to produce structural components to achieve higher in-service strength using higher strength aluminum alloys. Two of the commonly used high strength aluminum alloys, AA6111 and AA7075, are being considered for elevated temperature sheet forming applications. With more aluminum applications in vehicle and good recyclability of aluminum components, there is a concern of contamination from transition metals such as Fe, Mn and Cr from vehicle end of life scraps getting into aluminum scrap stream. Such impurity elements can have profound impact on aluminum alloy’s mechanical properties, performance and formability at room and elevated temperatures. This study is focused on variants of AA6111 and AA7075 alloys with increased recycling content, and thus higher amounts of the above transition metals. The objective is to investigate the effect of impurity alloying elements on final microstructure, mechanical properties and formability of the above sheet materials. Formability is studied in terms of sheet bendability and elevated temperature forming limit diagrams (FLDs) using a hot gas bulge tester. / Thesis / Master of Applied Science (MASc)

Das Freiformschmieden ist eines der ältesten Umformverfahren in der Geschichte, das kontinuierlich durch technische Innovationen weiterentwickelt wurde. Die rasante Entwicklung in den Bereichen der Mess- und Regelungstechnik sowie der Rechenkapazität von IT-Systemen in den letzten Jahrzehnten bietet die Möglichkeit, das Freiform-schmieden auf seine nächste Entwicklungsebene zu heben. Um einen vollautonomen Schmiedeprozess zu etablieren, wird am Institut für Metallformung der TU Bergakademie Freiberg eine Schmiedezelle eingerichtet. Diese Verfügt über zwei Schmiedepressen, einen Ofen und einen Roboterarm vom Typ KR 360 L280-2 der Firma KUKA mit einer Traglast von bis zu 280 kg als Manipulator. Mithilfe eines 3D-Scansystems ist es möglich die Werkstückgeometrie zwischen einzelnen Stichen oder gar Pressenhüben zu erfassen. Weiterhin verfügt das Scansystem über drei Wärmebildkameras, welche während eines Scans die Oberflächentemperatur erfassen. Die einzelnen Komponenten der Schmiedezelle werden über einen Zentralrechner gesteuert.