Friction Stir Welding (FSW) is a rapidly growing solid state welding process and has been a proven method for welding high strength aluminium alloys which were formerly not recommended for joining by conventional fusion welding methods. Based on the information acquired from previous studies, to obtain a defect free Friction Stir (FS) weld with suitable strength, three basic requirements need to be fulfilled (i) Filling of the cavity created behind the tool pin during its traverse and ensuring satisfactory contact of filled material with newly generated surface (on advancing side trailing edge of the pin) (ii) Disrupting and distributing the oxide layer at the initial weld interface (iii) Adequate level of mixing of both side material (Adjacent and Retreating side) in similar welding. In the case of dissimilar welding mixing is desired in controlled amount (to prevent or curtail formation of intermetallics) depending on material combination. Failure to achieve the first precondition results in void. Second and third precondition are interconnected for similar FSW as adequate mixing in weld helps in disruption and distribution of oxide layer at initial weld interface. Failure to achieve this, results in Joint Line Remnant (JLR). Metal to metal contact cannot be established due to the presence of JLR (aligned oxide particles) and subsequently initial interface is left unwelded which deteriorate the static and dynamic strength of friction stir welds. The problem aggravates while friction stir welding materials with tenacious contaminant layer. Therefore, appropriate stirring (which entails large deformation and mixing) of initial weld interface is essential for successful FS welds. Hence, process aspects assisting mixing of adjacent (Advancing and Retreating side) materials need to identified and studied, which are missing in former studies. Experiments are conducted with classical FS tool (possessing frustum shaped/tapered circular pin) to analyse the effect of welding parameters (tool rotation speed, traverse speed, plunge depth, tool tilt and tool position w.r.t initial interface) and tool runout by changing these parameters over a range. Tool rotation speed, traverse speed, plunge depth and tool position with initial interface are changed continuously and tool tilt and tool runout are changed in discrete steps. Tool geometry is considered to be a prime parameter controlling the magnitude of mixing, as interaction of rotating tool with initial abutting base metal interface makes the process mechanism complex, unlike other solid state welding process, namely forge welding, diffusion welding, friction welding, explosive welding, ultrasonic welding and roll bonding. Furthermore, due to asymmetric nature of material flow in FSW process, the material located in different locations with respect to the tool is subjected to different levels of deformation. For this purpose experiments have been carried out to analyse the effect of different tool geometrical aspects on level of mixing and material flow. On the other hand, visualizing flow and mixing in metals is debatable as insertion of marker material in the weld line can alter the nature of material flow in the weld due to different material flow characteristics of the base and marker materials and introduction of additional interfaces. Further, using dissimilar materials for flow studies cannot be considered for comparison with similar friction stir welds as their flow properties are different. Therefore, an alternate experimental strategy is devised in these studies using physical modelling approach which is effective and helps in identifying and quantifying mixing observed under different tooling and process conditions. In the present investigation, plasticine of primary colours is adopted and the hue attribute of colour is used to study and quantify intermixing. Yellow and Blue plasticine are placed on advancing and retreating sides respectively. The degree of mixing is indicated by the intensity of generated green. Digital images of the cross section in weld nugget region are taken. To obtain hue component of these digital images the RGB color-maps are converted to HSV color-maps. Overall, these studies help in formulating the guidelines which are useful during tool design, and administering the process to obtain a defect free well mixed welds. Based on the experimental results following conclusions are derived. 1. Following process aspects: tool geometry, interface offset, tool rotation and tool runout demonstrate a significant impact on material mixing and breaking and dispersion of initial interface in weld nugget. Tool tilt, plunge depth, tool traverse exhibit negligible effect on degree of mixing. 2. Increase in tool rotation speed (with other parameters fixed) improves mixing substantially but can be increased to a certain limit after which voids emerge due to loss of weld nugget material in the form of flash. 3. Reducing the weld pitch (i.e. increasing tool rotation speed for a given tool traverse speed) reduces the size of the weld nugget and vice versa. Tool traverse speed largely affects advancing side material and rotation speed affects retreating side material. Therefore, for higher weld pitch advancing side material (yellow plasticine) dominates the weld nugget, whereas for lower weld pitch retreating side material (blue plasticine) dominates the weld nugget. 4. The extended macro-structural feature commonly observed in FS welds occurs under influence of plunge depth. Consequently, this macro-structural feature serves as the demarcation point between shoulder affected and pin induced material flow in FS weld. 5. The degree of mixing and subsequent elimination of JLR, improves, when original interface is offset on the advancing side w.r.t tool axis for all the tools investigated in the present study. Triangular and square pin generate larger pin induced mixing which intensifies further with interface on advancing side, indicating tools with such profiles to possess larger safe zone with better mixing characteristics 6. At zero interface offset with all the process parameters fixed, tapered triangular and square pin profile tools produce welds with maximum mixing. For pins with faces, material is transported in lumps around the pin. The size of lump increases with lesser number of faces on pin. Material in the vicinity of the pin experiences spinning/whirling movement. The volume of material experiencing spinning in a single tool revolution depends on (a) weld-pitch (lesser volume of material for smaller weld pitch and vice versa) and (b) number of faces on the pin (lesser volume of material for greater number of faces and vice versa). Therefore, circular pin which can be considered to be made of infinite faces, spinning of material occurs at micro level for relatively smaller weld pitch. 7. For classical FS tool (tapered circular/frustum shape), there exists an optimum ratio (shoulder diameter/pin diameter) situated between 2.7 to 3.6 to produce void free well mixed welds. Tools with ratio of 2.7 and below possess a tendency to produce welds with void but with better mixing in weld region. Tools with ratio of 3.6 and above possess a tendency to produce void free welds but with poor mixing in weld region. Voids appear and grow under following circumstances (a) with increase in pin diameter (for a fixed shoulder diameter), (b) with decrease in shoulder diameter (for a fixed pin diameter), (c) with decrease in pin taper (for a fixed shoulder diameter and top diameter of pin). Pin length has no effect on void formation. However, it is obvious, length of root defect increases with decrease in pin length. The tooling guidelines established in this study through plasticine work can be extended to metallic friction stir welds of various thickness plates by proportionately increasing or decreasing the tool dimensions as long as they fall in the recommended range. 8. Smaller pin diameter tools exhibit higher optimum weld pitch (but with lower degree of mixing) when compared to larger pins (but with higher degree of mixing). Optimum weld pitch represents weld pitch resulting in void free welds. Consequently, tools with higher optimum weld pitch help in welding at a better rate. 9. Tool runout is replicated through tools with eccentric pins. It is interesting to note that, all the tools with pin eccentricities do not assist in mixing but tools with only certain eccentricities (0.3 and 0.6mm assisted in mixing in the present investigation). It implies that tool runout of certain values facilitate mixing in weld. On the other hand density of void increases with eccentricity of pin/tool runout. 10. In dissimilar FSW investigated with plasticine A, B, C and D possessing different flow stresses (flow stresses ascending in the order of A, B, C and D) and strain rate sensitivity of 0.24, 0.22, 0.19 and 0.18 respectively, following inferences are drawn (i) For combination A and B, weldability improves when plasticine B is on Advancing Side (AS) and A is on Retreating Side (RS). The level of mixing also improves when interface is on AS (w.r.t tool axis) for this handedness. On the contrary, severe discontinuities emerge when plasticine B is on RS and A is on AS, especially when interface is closer to the tool pin axis. (ii) For combination A and C, weldability improves when C is on AS and A is on RS. The level of mixing also enhances when interface is on AS (w.r.t tool axis) for this handedness. (iii) For combination A and D, joining is poor for both the handedness. However, nature of defect is different in both the combinations. Cracks are observed when A is located on AS and voids emerge when D is located on AS. On the other hand, placing A on AS results in weld thinning. (iv) For combination B and C, there is no appreciable change in terms of weldability and level of mixing. Both the handedness in this combination yielded fairly similar results. (v) For combination B and D, though discontinuities do not emerge with change in handedness, mixing in weld improves when B is on AS unlike to its location on RS. (vi) For combination C and D, there is no appreciable change in terms of defect formation and level of mixing with change in handedness. Both the handedness in this combination yield fairly similar results.

A procura cada vez mais intensa por redução de peso e consequente diminuição do consumo de combustível dos veículos automotores e aeronaves, tem proporcionado um crescimento constante na utilização do alumínio e suas ligas nos diversos setores da indústria de manufatura. No entanto, a dificuldade de união em juntas de alumínio que atendam requisitos de alta resistência à fratura e à fadiga, tem intensificado as pesquisas por novas tecnologias em seu processo de soldagem. Neste contexto, o processo de soldagem denominado Friction Stir Welding (FSW), vem ganhando espaço nas pesquisas e também na indústria. Neste processo, uma ferramenta não consumível é projetada especialmente para ser introduzida nas juntas das chapas a serem soldadas, gerando calor e misturando mecanicamente o material da junta, consolidando a solda. Este trabalho teve como objetivo avaliar os efeitos dos parâmetros de soldagem FSW, na consolidação das propriedades mecânicas das soldas produzidas, na microestrutura, além de buscar a otimização do processo para a liga em estudo. Para tanto, a geometria da ferramenta foi projetada, fabricada e testada, de forma a definir os parâmetros ideais para obtenção de juntas soldadas sem defeitos. Uma máquina fresadora CNC foi utilizada para a execução dos testes. As soldas foram produzidas em chapas de alumínio da liga Al 5182-O com espessura de 3,25mm, com velocidade rotacional da ferramenta mantida constante em 500 rpm e velocidades de soldagem de 50, 100, 150, 200 e 250 mm/min. A ferramenta foi inclinada em um ângulo de 1º, todas as soldas foram realizadas com sentido horário de rotação, após a realização dos testes as juntas soldadas foram submetidas a uma série de ensaios destrutivos e não destrutivos caracterizando cada teste realizado. Juntas de topo com penetração completa e livre de defeitos foram produzidas com velocidades de soldagem de 100, 150, 200 e 250 mm/min, enquanto com a velocidade de soldagem de 50 mm/min resultou em defeito do tipo vazio na zona da mistura no lado do avanço, defeito este caracterizado através de inspeção por microtomografia, o que fez com que as soldas produzidas com esta velocidade de soldagem rompessem na junta soldada. Em todas as velocidades de soldagem a caracterização através de microscopia óptica na seção transversal das soldas revelou um refino microestrutural, obtido pelo fenômeno de recristalização dinâmica, que resultou em um aumento nos valores de dureza na zona da mistura. Os resultados obtidos demostram que soldas de boa qualidade podem ser produzidas com este processo. Além disso, foi estabelecida uma correlação entre a história térmica associada ao processo de FSW, a microestrutura produzida e o desempenho mecânico das juntas soldadas. / The increasingly intense demand for weight reduction and consequent reduction of the fuel consumption of motor vehicles and aircraft , has provided a steady growth in the use of aluminum and its alloys in various sectors of the manufacturing industry , but the difficulty in joining together aluminum that meet high fracture resistance and fatigue , has intensified the research for new technologies in the process of welding. In this context , the welding process called Friction Stir Welding ( FSW ) has been gaining ground in research and also in industry . In this process , non-consumable tool is specially designed to be inserted in the joints of the plates to be welded, generating heat and mechanically mixing the gasket material, consolidating the weld. This study aimed to evaluate the effects of welding parameters FSW , the consolidation of the mechanical properties of the welds produced, microstructure, and seek to optimize the process for the alloy under study. For this, the geometry of the tool is designed, manufactured and tested in order to define the optimal parameters for obtaining welded joints without defects. A milling machine CNC was used for the tests. The welds were produced in sheets of aluminum alloy Al 5182-O with a thickness of 3,25mm with rotational speed of the tool maintained constant at 500 rpm and welding speeds of 50, 100, 150, 200 and 250 mm / min, the tool was tilted at an angle of 1°, all welds were performed with clockwise direction of rotation, after the tests the welded joints were subjected to a series of destructive testing and nondestructive characterizing each test performed. Butt welding with full penetration and free defects were produced with welding speeds of 100, 150, 200 and 250 mm / min, while with the welding speed 50 mm / min resulted in failure of the void type in the zone of the mixture side of the advance, this defect characterized by inspection by microtomography, which has meant that the welds produced with this welding speed would break the joint weld. In all welding speeds characterization by optical microscopy in cross section of welds revealed a microstructure refining, obtained by dynamic recrystallization phenomenon, for which resulted in an increase in the hardness values in the mixing zone. The results demonstrate that good quality welds can be produced with this process. Moreover, a correlation between the thermal history associated with the process produced the microstructure and mechanical performance of welded joints was established.

A procura cada vez mais intensa por redução de peso e consequente diminuição do consumo de combustível dos veículos automotores e aeronaves, tem proporcionado um crescimento constante na utilização do alumínio e suas ligas nos diversos setores da indústria de manufatura. No entanto, a dificuldade de união em juntas de alumínio que atendam requisitos de alta resistência à fratura e à fadiga, tem intensificado as pesquisas por novas tecnologias em seu processo de soldagem. Neste contexto, o processo de soldagem denominado Friction Stir Welding (FSW), vem ganhando espaço nas pesquisas e também na indústria. Neste processo, uma ferramenta não consumível é projetada especialmente para ser introduzida nas juntas das chapas a serem soldadas, gerando calor e misturando mecanicamente o material da junta, consolidando a solda. Este trabalho teve como objetivo avaliar os efeitos dos parâmetros de soldagem FSW, na consolidação das propriedades mecânicas das soldas produzidas, na microestrutura, além de buscar a otimização do processo para a liga em estudo. Para tanto, a geometria da ferramenta foi projetada, fabricada e testada, de forma a definir os parâmetros ideais para obtenção de juntas soldadas sem defeitos. Uma máquina fresadora CNC foi utilizada para a execução dos testes. As soldas foram produzidas em chapas de alumínio da liga Al 5182-O com espessura de 3,25mm, com velocidade rotacional da ferramenta mantida constante em 500 rpm e velocidades de soldagem de 50, 100, 150, 200 e 250 mm/min. A ferramenta foi inclinada em um ângulo de 1º, todas as soldas foram realizadas com sentido horário de rotação, após a realização dos testes as juntas soldadas foram submetidas a uma série de ensaios destrutivos e não destrutivos caracterizando cada teste realizado. Juntas de topo com penetração completa e livre de defeitos foram produzidas com velocidades de soldagem de 100, 150, 200 e 250 mm/min, enquanto com a velocidade de soldagem de 50 mm/min resultou em defeito do tipo vazio na zona da mistura no lado do avanço, defeito este caracterizado através de inspeção por microtomografia, o que fez com que as soldas produzidas com esta velocidade de soldagem rompessem na junta soldada. Em todas as velocidades de soldagem a caracterização através de microscopia óptica na seção transversal das soldas revelou um refino microestrutural, obtido pelo fenômeno de recristalização dinâmica, que resultou em um aumento nos valores de dureza na zona da mistura. Os resultados obtidos demostram que soldas de boa qualidade podem ser produzidas com este processo. Além disso, foi estabelecida uma correlação entre a história térmica associada ao processo de FSW, a microestrutura produzida e o desempenho mecânico das juntas soldadas. / The increasingly intense demand for weight reduction and consequent reduction of the fuel consumption of motor vehicles and aircraft , has provided a steady growth in the use of aluminum and its alloys in various sectors of the manufacturing industry , but the difficulty in joining together aluminum that meet high fracture resistance and fatigue , has intensified the research for new technologies in the process of welding. In this context , the welding process called Friction Stir Welding ( FSW ) has been gaining ground in research and also in industry . In this process , non-consumable tool is specially designed to be inserted in the joints of the plates to be welded, generating heat and mechanically mixing the gasket material, consolidating the weld. This study aimed to evaluate the effects of welding parameters FSW , the consolidation of the mechanical properties of the welds produced, microstructure, and seek to optimize the process for the alloy under study. For this, the geometry of the tool is designed, manufactured and tested in order to define the optimal parameters for obtaining welded joints without defects. A milling machine CNC was used for the tests. The welds were produced in sheets of aluminum alloy Al 5182-O with a thickness of 3,25mm with rotational speed of the tool maintained constant at 500 rpm and welding speeds of 50, 100, 150, 200 and 250 mm / min, the tool was tilted at an angle of 1°, all welds were performed with clockwise direction of rotation, after the tests the welded joints were subjected to a series of destructive testing and nondestructive characterizing each test performed. Butt welding with full penetration and free defects were produced with welding speeds of 100, 150, 200 and 250 mm / min, while with the welding speed 50 mm / min resulted in failure of the void type in the zone of the mixture side of the advance, this defect characterized by inspection by microtomography, which has meant that the welds produced with this welding speed would break the joint weld. In all welding speeds characterization by optical microscopy in cross section of welds revealed a microstructure refining, obtained by dynamic recrystallization phenomenon, for which resulted in an increase in the hardness values in the mixing zone. The results demonstrate that good quality welds can be produced with this process. Moreover, a correlation between the thermal history associated with the process produced the microstructure and mechanical performance of welded joints was established.

O processo de soldagem por fricção e mistura (FSW) tem despertado grande interesse nos últimos anos e tornou-se uma alternativa para unir materiais de baixa soldabilidade, como as ligas de alumínio das séries 2XXX e 7XXX, as quais são empregadas na estrutura das aeronaves, por possuírem elevada relação resistência/peso. O processo FSW, todavia, causa mudanças microestruturais nos materiais soldados, particularmente na zona misturada (ZM) e nas zonas termicamente (ZTA) ou termomecanicamente (ZTMA) afetadas. Estas mudanças geralmente interferem no desempenho frente à corrosão das ligas soldadas. No presente estudo, a resistência à corrosão das ligas de alumínio 2024-T3 e 7475-T761, unidas pelo processo FSW foi investigada em solução 10 mM de NaCl. Ensaios de visualização em gel ágar-ágar e de imersão associados a técnicas microscópicas foram realizados para investigar o efeito do acoplamento galvânico na corrosão das diferentes regiões da junta soldada. Os resultados do ensaio de visualização em gel mostraram que, quando acopladas, a liga 2024 atua como cátodo e a 7475 como ânodo. Os ensaios de imersão revelaram acoplamento galvânico entre as ligas na zona misturada (ZM). A região mais afetada pela corrosão foi a ZTMA da liga 7475, com corrosão intergranular desde as primeiras horas de imersão. A influência do processo de soldagem na resistência à corrosão das duas ligas de alumínio foi investigada por ensaios eletroquímicos. Os ensaios eletroquímicos adotados foram medidas de potencial de circuito aberto (PCA) em função do tempo de exposição ao meio corrosivo, espectroscopia de impedância eletroquímica (EIE) e curvas de polarização potenciodinâmica. Os ensaios de polarização mostraram elevada atividade eletroquímica na zona de mistura indicada pelos altos valores de densidade de corrente em comparação com as demais zonas testadas. Os resultados de EIE globais mostraram que nas primeiras horas de exposição ao eletrólito o processo de corrosão foi predominantemente controlado pela liga 7475; todavia, com o tempo de exposição ao eletrólito, a corrosão passou a ser controlada pela liga 2024. / Friction stir welding (FSW) has roused great interest in recent years and it is now an alternative for joining materials of low weldability, such as the aluminum alloys of the 2XXX and 7XXX series, used in the aircrafts structure due to their high strength /weight ratio. However, FSW causes material microstructural changes, mainly in the stir zone (SZ), the heat affected zone (HAZ) or thermomechanically (TMAZ) affected zones of the materials welded. These generally interfere with the corrosive performance of the welded joint. In the present study, the corrosion resistance of the 2024-T3 and 7475-T761aluminum alloys, joined by FSW was investigated in 10 mM NaCl electrolyte. Agar-agar gel and immersion tests associated with microscopic techniques were performed to investigate the effect of galvanic coupling between the welded materials. Results from this test showed that, when galvanically coupled, the 2024 alloy acts as cathode and the 7475 as anode. Immersion tests revealed galvanic coupling between the alloys in the SZ. The zone most susceptible to corrosion was the TMAZ of the 7475. Intergranular corrosion was observed in this zone since the first hours of immersion. The influence of the welding process on the corrosion resistance of the alloys was also evaluated by electrochemical tests. The electrochemical tests adopted were open circuit potential measurements (OCP) as a function of time of exposure to the electrolyte, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. The polarization tests showed high electrochemical activity in the stir zone indicated by the high current densities measured comparatively to the other tested zones. The global EIS results indicated that in the first few hours of exposure to the electrolyte the corrosion process was predominantly controlled by the 7475 alloy; however, with time of exposure to the electrolyte, the corrosion was controlled by alloy 2024.

O processo de soldagem por atrito linear com mistura (FSW) é uma técnica recente para a soldagem no estado sólido de materiais, em particular para o alumínio e suas ligas. O processo foi inventado na Inglaterra em 1991. Neste processo, as partes a serem soldadas são fixadas e uma ferramenta especial realiza a soldagem de forma contínua. A ferramenta possui uma velocidade de rotação e, durante a sua translação, o material é misturado no estado sólido e, conseqüentemente, soldando as duas partes. A junta soldada por FSW de alumínio AA 6063-T6, com espessura de 3 mm foi caracterizada. A soldagem foi realizada com uma rotação da ferramenta de 710 rpm e com uma velocidade de translação de 5,3 mm/s. A ferramenta empregada é do tipo three flats, com diâmetro do ombro de 14 mm, diâmetro do pino de 3 mm e com ângulo de 90° com relação à horizontal. Os corpos de prova foram soldados em três condições: um passe, dois passes e dois passes com inversão de rotação do pino. Após a soldagem foram realizados os seguintes tratamentos térmicos: solubilização, envelhecimento e recozimento. A junta soldada foi caracterizada por macrografias, micrografias, microdureza, ensaios de calorimetria diferencial e EBSD. Os resultados mostraram que existem ZTMAs diferentes conforme a condição dos de passes. O número de passes tem influência nas componentes da textura alterando de Cubo para Latão e para Goss + Cobre. Os tratamentos térmicos de envelhecimento e recozimento produziram as maiores e menores durezas do cordão, respectivamente. Foi observada a sinergia entre os fatores número de passes e região do cordão no tamanho de grão do cordão. O lado de retrocesso, após o tratamento térmico, apresentou os grãos mais finos. / Friction stir welding (FSW) is a recent process for aluminium welding in solid state. This process was invented in England in 1991. The welding process is done with a special rotating tool that travels along the joint while the parts are fixed. The tool has a speed and a rotation and during its translation the material mixtures in solid state and the joint occurs. The objective of this paper is to show the metallurgical and mechanical characteristics of a 3 mm thick Aluminum AA 6063 T6 plate welded joint. The tool rotation speed was 710 rpm and the translation speed was 5.3 mm/s. The type of the tool used was three flats, with a shoulder diameter of 14mm and pin diameter of 3mm and perpendicular to the plate. The samples were welded in three conditions: one pass, two passes and two passes with pin rotation inversion in the second pass. The welded samples were also submitted to solution heat treatment, solution heat treatment followed by aging and annealing heat treatments. The welded joint was studied with these main experimental techniques: optical and scanning electron microscopy, microhardness, differential scanning calorimetry and electron backscatter diffraction for texture analysis. The results showed different TAZs according to the welding conditions. The number of passes has influence over the texture components changing from Cube to Brass and to Goss + Copper. The aging and solution heat treatments showed the highest and the lowest hardness, respectively. Synergy between the welding conditions and weld region was observed for the grain size results. The retreating side produced the finest grains after heat treating.

Esta tese tem por objetivo a aplicação do processamento por atrito linear na liga de titânio Ti-6Al-4V. Derivado da solda por atrito linear, é um processo recente desenvolvido na década de 90 para união de alumínio. Sua aplicação em outros tipos de materiais como aços e ligas de alto desempenho, em especial o titânio, tem interessado a industria. A metodologia utilizada nesta tese para avaliar o processamento por atrito linear, consistiu na execução de ensaios mecânicos de tração em condições mistas em chapas da liga de titânio Ti-6Al-4V. A máquina utilizada para o processamento das chapas foi um centro de usinagem CNC convencional, adaptado com dispositivos especiais. Além dos ensaios de tração em condições mistas, foram executadas medições de microdurezas nas regiões atingidas pelo processo, avaliação das microestruturas resultantes e medições de tensão residual para uma caracterização mais ampla do processo. As microestruturas na região processada são caracterizadas por uma estrutura totalmente transformada. As temperaturas de pico na região processada excederam a temperatura -transus durante o processamento e a transformação da fase + ocorreu durante a fase de resfriamento. A transformação da fase para resultou na formação de agulhas de fase nos contornos e pelo interior dos grãos da fase . Pequenas regiões com estrutura equiaxial de grãos ( globular) foram observados na zona de processamento. A abordagem dos resultados quantitativos foi feita de forma estatística, visando identificar os parâmetros de maior interação com os resultados observados. Foi identificado nesta tese que a rotação da ferramenta apresentou a maior influência nos resultados de tensão residual, microdureza e tensão de escoamento. Uma importante contribuição à modelagem da tensão de escoamento para materiais anisotrópicos é proposta, baseado em um critério de escoamento ortotrópico. Equações complementares baseadas nos testes mistos de tração e cisalhamento são propostas para modificar o modelo ortotrópico. O intuito deste modelo é indicar em que condições o material tem seu regime de escoamento atingido, podendo servir de base para simulações práticas de peças em condições similares. / This thesis aims at the application of friction stir processing (FSP) in Ti-6Al-4V titanium alloy. Derived from friction stir welding (FSW), it is a recent process developed in the 90s for aluminum joining. Its application to other types of materials such as steel and high performance alloys, in particular titanium, has interested industry. The methodology applied in this thesis to evaluate FSP, consisted in the execution of tensile test at mixed conditions to Ti-6Al-4V sheets 4. The machine used for processing the sheet was a conventional CNC milling machine, assembled with special fixture devices. In addition to tensile tests, measurements have been performed to the regions affected by the process such as evaluation of microhardness, microstructure and residual stress condition. The microstructures at the processed region are characterized by a transformed structure. The peak temperatures, in the processed region, exceeded the -transus temperature during the processing and transformation of the phase + occurred during the cooling phase. This transformation resulted in the formation of boundary and intergranular phase (Widmanstätten) at the grains. Small regions of equiaxed grain structure (globular ) were observed in the processed zone. The approach to the quantitative results was made in statistical form aiming to identify the parameters interaction with the observed results. It was identified in this thesis that the tool spinning rotation showed the highest influence on the results of residual stress, hardness and yield strength. An important contribution to the modeling of anisotropic materials yield stress is proposed based on an orthotropic yield criterion. Additional equations based on the mixed tests for tensile and shear are proposed to modify the orthotropic model. The purpose of this model is to indicate the conditions under which the material has reached its yield regime, and may be a basis for practical simulations in similar conditions.

Orientador: Janito Vaqueiro Ferreira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T16:12:48Z (GMT). No. of bitstreams: 1 ArcilaGago_ManuelFelipe_M.pdf: 7192169 bytes, checksum: 7b23a08769656a07765344e20d1f6ad4 (MD5) Previous issue date: 2013 / Resumo: A variedade de materiais no setor aeronáutico para redução de peso e custo tem se proliferado a um grau intensivo, onde têm sido revisadas diferentes pesquisas para encontrar outros tipos de materiais de fácil maneabilidade para construção de peças que satisfazem as restrições impostas. Assim, existe uma procura constante de soluções para facilitar a produção, e ao mesmo tempo aumentar a segurança das aeronaves levando em consideração pontos importantes como a fadiga e ruptura do material. Um material frequentemente utilizado que atende a estes requisitos devido a suas propriedades de densidade e resistência é o alumínio, e é neste ambiente que existe um processo de manufatura utilizado para a soldagem conhecido como "Friction Stir Welding" (FSW). No presente momento, estudos para criação de modelos que representem características mecânicas utilizadas em projetos em função de parâmetros do processo tem sido pesquisados. Embora este processo seja de difícil modelagem devidos as suas complexidades, tem sido estudado e utilizado diferentes algoritmos que possibilitem o melhoramento da representação do modelo, tais como os relacionados com máquinas de aprendizagem (ML) e suas diferentes otimizações. Neste contexto, a presente pesquisa tem seu foco na obtenção de um modelo baseado no algoritmo de aprendizagem de Máquina de Vetores de Suporte (SVM), e também com outros algoritmos tais como Regressão Polinomial (RP) e Rede Neural Artificial (RNA), buscando encontrar modelos que representem o processo de soldagem por FSW através das propriedades mecânicas obtidas pelos ensaios de tração e por análise de variância (ANOVA), entendendo suas vantagens e, posteriormente, recomendar quais dos algoritmos de aprendizagem tem maior beneficio / Abstract: In the aerospace industry to reduce weight and cost, a great quantity of materials has been used, which has generated research to find types of materials, that have been better maneuverability and to guarantee the properties required to development of pieces for the industry. Thus, the studies look for optimize between production easiness and increase the aircraft safety, taking into consideration important issues such as fatigue and fracture of the materials. One of the most common approach used is aluminum by their mechanical properties (density and strength), although it has many problems to be welding with the traditional methods. Currently, the Friction Stir Welding (FSW) process is used in the industry, as well in the academy. However, the FSW is difficult to model by the complexities in the physical phenomenal occurred during the weld process, as result, has been studied and used different algorithms that allow enhance the model representation. The Machine Learning (ML) is a methodology studied to obtain the model optimized. In this context, the present research focus by to obtain a model-based in learning algorithm using Support Vector Machine (SVM). Although comparisons were made with other algorithms such as Polynomial Regression (PR) and Artificial Neural Network (ANN), searching to find models that represent the FSW process weld using the mechanical properties obtained by tensile tests and analysis of variance (ANOVA). Finally, conclusions to understand the advantages learning algorithms are presented / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Le soudage par friction malaxage « Friction Stir Welding » est un procédé d'assemblage de pièces en phase semi solide. Le cordon de soudure est obtenu grâce à un outil de révolution composé d'un épaulement et d'un pion. Ce procédé utilise le principe de la conversion de l'énergie mécanique en énergie thermique par frottement de l'outil avec les pièces à assembler. Ce travail de thèse est une contribution à la modélisation expérimentale et à la simulation numérique de ce procédé permettant de fournir des modèles pour aider à la compréhension des phénomènes thermiques et mécaniques ainsi que les interactions entre les paramètres de soudage. Les études expérimentales sont principalement orientées vers la caractérisation de l'écoulement de matière à l'aide de marqueurs et vers l'optimisation des paramètres du procédé. L'effet de la géométrie de l'outil (outil à pion cylindrique ou outil avec méplats) sur l'écoulement de la matière au cours du soudage est étudié. Pour représenter la géométrie de l'écoulement et prédire les champs thermiques et mécaniques à l'état stationnaire, des modèles formulés sur la base de la dynamique des fluides sont adoptés dans la présente thèse. Deux modèles thermomécaniques sont développés: (1) un premier modèle numérique construit sous Fluent permet d'étudier le comportement thermomécanique et l'écoulement au cours du soudage FSW. Une loi de comportement dépendante de la température et de la vitesse de déformation est utilisée et une discussion sur les conditions de contact entre l'outil et les plaques à souder est présentée. Les résultats de l'écoulement sont comparés avec ceux obtenus expérimentalement dans le cas de suivi des trajectoires de particules de cuivre. (2) un deuxième modèle original basé sur une procédure itérative est mis en œuvre permettant le soudage de plaque de grandes dimensions. En effet, pour une meilleure prise en compte des conditions aux limites thermiques, un modèle thermomécanique construit autour de l'outil de soudage et couplé avec un modèle thermique pour tout le reste du domaine étudié. Ce modèle permet de prendre en compte le transfert de chaleur dans l'outil et dans la plaque support. Les cycles thermiques et la plage de viscosité pour deux alliages d'aluminium (AA7020-T6 et AA6061-T3) sont analysés et comparés avec succès aux résultats expérimentaux. Les efforts et le couple de soudage calculés numériquement sont validés par rapport à la littérature. / The friction stir welding is a process for assembling a semisolid phase parts. The weld seam is achieved by a revolution tool consists of the shoulder and the pin. This process converts the mechanical energy into heat energy by friction of the tool with the parts to be joined.This thesis is a contribution to the experimental modeling and numerical simulation of this process in order to provide models to assist in understanding the thermal and mechanical phenomena and interactions between the welding parameters. Experimental studies are used for the characterization of the material flow with markers and to optimize the process parameters. The effect of tool geometry (cylindrical pin or tool with flats) on the material flow during welding is studied. To represent the flow geometry and predict the thermal and mechanical fields in the steady state, CFD models are adopted in this thesis. Two thermomechanical models are developed: (1) first numerical model is used to study the thermomechanical behavior and flow during FSW. FLUENT is employed to solve the coupled thermal and fluid flow equations. A behavior law depending on temperature and strain rate is used and a discussion on the contact conditions between the tool and the workpieces is presented. The results of the flow are compared with those obtained experimentally in the followed case of trajectories copper particles. (2) A second original model based on iterative procedure is implemented to welding large plates. To take account the correctly thermal boundary conditions, a thermomechanical model built around the welding tool and coupled with a thermal model for the rest of the area studied. This model allows taking into account the transfer of heat in the tool and in the backing-bar. Thermal cycles and the viscosity range for two aluminum alloys (AA7020-T6 and AA6061-T3) are successfully analyzed and compared with experimental results. The loads and torque welding are calculated numerically and validated in the literature.

I och med ökad konkurrens och ökade kundkrav behöver företag bedriva produktutveckling med en rapid approach. ESAB:s sätt att svara upp mot dessa krav har resulterat i ett brett produktsortiment av friktionssvetshuvuden. Deras långsiktiga mål är därför att inrätta en ny standard för att reducera kostnader. Planen är därför att aktivt bedriva produktutveckling tillsammans med universitet och högskolor runt om i landet. Detta produktutvecklingsprojekt kan beskrivas som en första etapp i ett hållbart produktutvecklingsarbete på ESAB mot ett långsiktigt mål om att sätta en ny standard inom FSW. Syftet med detta examensarbete är att analysera två friktionssvetshuvuden: FSW LEGIO 4UT och FSW LEGIO 5UT genom K-FMEA och DFA2. Därigenom kartlägga vilka potentiella brister som finns i de befintliga konstruktionerna och belysa var bristerna finns. Analysresultatet ska tillsammans med produktutvecklingsteori, forma ett informationsunderlag för bedrivande av fortsatt produktutvecklingsarbete. Tillvägagångssättet har bedrivits genom tre faser: 1) uppstart/förarbete, 2) genomförande och 3) avslut/presentation. Vetenskapssynen har präglats av positivism med vissa inslag av hermeneutik. Forskningsmetoden har både vad gäller datainsamling, analysmetodik och utvärderingsmetodik varit kvalitativ. Undersökningsansatsen har varit av abduktiv art medan undersökningsinriktningen har varit kombinerad explorativ och deskriptiv. Först analyserades ritningsunderlag, komponentlistor, STEP-filer och produktspecifikationer för sammanlagt åtta svetshuvuden. Ett strategiskt urval av tre gjordes för att sedan ytterligare exkludera ett av dessa. En djupdykning gjordes i det empiriska underlaget som gav upphov till två hypoteser: 1) komponenter som under drift är i rörelse torde vara högst belägna att utsättas för fel, 2) svetshuvudena kan möjligen komprimeras volymmässigt och komponenter reduceras till antalet. En semi-strukturerad fokusgruppintervju genomfördes för fyra respondenter med teknisk expertis på området. Resultatet av denna gjorde att hypoteserna kunde bekräftas. Detta empiriska datamaterial ställdes mot befintlig teori rörande K-FMEA och DFA2. Vidare utfördes K-FMEA enligt teorin i sju steg på såväl systemnivå som komponentnivå. Sedan gjordes detsamma för DFA2 vars arbetssätt sker i fyra steg. Resultatet av denna studie påvisar att de allra mest kritiska komponenterna rör spindeln, spindelhuset och lager. Påfrestningar finns också i hydrauliken som har tilldelats höga kriticitetstal. Det finns även feltyper med hög risk relaterat till tillverkning och montering. Vad gäller DFA2 visade resultatet att de befintliga konstruktionerna har låg grad av monteringsvänlighet. Detta då flera monteringsriktningar används, flera komponenter är stora, tunga och svårhanterade. En del komponenter har svåråtkomlig monteringsplats. Vidare behövs för vissa komponenter extra hjälpmedel och verktyg för att kunna genomföra monteringen. Rekommendationen till ESAB i en potentiell andra etapp av detta produktutvecklingsarbete, vore att komplettera denna studie med andra produktutvecklingsverktyg och kostnadskalkyler. Detta för att se till att göra rätt från början och eliminera risker för eventuella efterföljande kostsamma justeringar. / With increased competition and increased customer requirements, companies need to pursue product development with a rapid approach. ESAB’s way of responding to these demands has resulted in a wide product range of friction welding heads. Their long-term goal is therefore to set a new standard to reduce costs. The plan is to actively conduct product development together with universities in Sweden. This product development project can be described as a first step in sustainable product development work at ESAB towards a long-term goal of setting a new standard within FSW. The purpose of this thesis is to analyze two friction welding heads: FSW LEGIO 4UT and FSW LEGIO 5UT through K-FMEA and DFA2. Thereby, identify the potential shortcomings found in the existing constructions and highlight where the shortcomings exist. The analysis results, together with product development theory, will form an information base for the pursuit of continued product development. The approach has been conducted through three phases: 1) start-up/pre-work, 2) implementation, and 3) completion/presentation. The science view has been characterized by a positivistic nature with elements of hermeneutic in some respects. The research method has been qualitative in terms of data collection, analysis methodology and evaluation methodology. The research effort has been abductive, while the research focus has been a combination of exploratory and descriptive. First, drawing documents, component lists, STEP files and product specifications were analyzed for a total of eight friction welding heads. A strategic selection of three was made to further exclude one more. An in-depth dive into the empirical evidence was made which gave rise to two hypotheses: 1) Components that move relative to others in welding operation, are most likely to be subject to errors; 2) These friction welding heads may possibly be compressed in terms of volume, and the components reduced to the number. A semi-structured focus group interview was conducted with a total of four respondents who have technical expertise in the field. The result of the interview allowed the hypothesis to be confirmed. The empirical data was put against the existing theory regarding K-FMEA and DFA2. Furthermore, K-FMEA was performed according to the theory in seven stages at both system level and component level. Then the same was done for DFA2, whose mode of operation takes place in four stages. The result of this thesis shows that the most critical components relate to the spider, spider house and the bearings. There are also stains in hydraulics that have been awarded high risk priority numbers. Along with that, failure modes with high risk frequencies related to manufacturing and assembly are identified. When it comes to DFA2, the result shows that the existing designs has low degree of assembly ease. This is because several mounting directions are used, several components are large, heavy and difficult to handle. Some components also have difficult access point. In addition, external equipment such as fixtures and tools, are needed to install some components. The recommendation to ESAB in a potential second step of their product development work, would be to complement this study with other product development tools and cost calculations. This to make sure to do right from the start and eliminate risks for any subsequent costly adjustments.

Dans le domaine aéronautique, le soudage par friction-malaxage (FSW – Friction Stir Welding) apparait comme un procédé innovant d’assemblage des fuselages, allégeant la structure avion en remplaçant la technique actuelle de rivetage. La simulation numérique est un support permettant de mieux comprendre et maîtriser ce procédé. L’alliage d’aluminium étudié dans ce projet est de type AA2024-T3 et tire principalement ses propriétés du durcissement structural. Modéliser l’évolution de la précipitation s’avère essentiel pour définir les propriétés finales de la soudure. Le modèle choisi doit prendre en considération les familles de précipités formés et les processus de germination, croissance et coalescence. Il doit être précis, robuste et rapide pour être applicable au procédé FSW. Un modèle de classe couplé à des calculs d’équilibre thermodynamiques a été choisi dans cette étude. Pour définir la cinétique de croissance d’un précipité, une cinétique de croissance initialement établie pour un alliage binaire a été étendue à un alliage multicomposé. Connaissant la distribution en taille des familles de précipités, les propriétés mécaniques sont définies selon un modèle empirique. La calibration anisotherme a été réalisée via un essai de DSC où signaux expérimentaux et simulés ont été comparés pour déterminer la teneur initiale des phases en présence et définir les paramètres matériaux de l’alliage. L’essai isotherme a établi le lien entre état de précipitation et propriétés mécaniques résultantes. Le modèle est appliqué à la simulation des évolutions microstructurales au cours d’une soudure FSW afin de prédire les propriétés finales du joint soudé. Les évolutions thermiques sont déterminées via l’utilisation d’un modèle macroscopique développé parallèlement dans une thèse, également portée par la Chaire Daher. Les données numériques obtenues sont comparées à des expériences instrumentées, montrant une bonne estimation des duretés. Les profils expérimentaux sont retrouvés, de même que les caractéristiques des différents domaines, validant l’approche et sa capacité à simuler efficacement les évolutions des processus de précipitation. / In the aeronautic industry, the friction stir welding (FSW) process is seen as an interesting option to lighten aircraft structure by replacing the standard riveting technology used to join parts. Numerical simulation is chosen to improve understanding of the different mechanisms occurring during FSW. The aluminum alloy studied is an AA2024-T3 grade. Its mechanical properties mainly derive from structural hardening mechanisms. An accurate model of precipitate evolution is essential to define hardness profile of the weld. The chosen simulation has to be robust and time-efficient in order to be suitable for the FSW process modeling. It must consider the two families of precipitates (GPB zones and S phase) and model nucleation, growth and coarsening phenomena. A PSD model is chosen and coupled with thermodynamic equilibrium calculations. To define the growth kinetics of precipitates, an exact analytical solution is extended to a multi-component alloy. Knowing the distribution of precipitates size, the mechanical properties are defined based on an empirical model. The amount and properties of phases are initialized through non-isothermal DSC calibration and comparison between experimental heat flux and simulated one. Isothermal test is selected to establish the link between precipitation state and mechanical properties. The model is applied to the simulation of microstructural evolution in FSW in order to predict the final properties of the weld. Thermal changes are determined through the use of a macroscopic model developed during a twin project within the Chair Daher. Numerical results are compared with instrumented experiments and show a good estimate of hardness. The experimental profiles are found, as well as the characteristics of the different areas. This validates the approach and its efficiency to simulate the evolution of the precipitation process.