Orientador: Renato Pavanello / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-20T12:22:43Z (GMT). No. of bitstreams: 1 Miyaura_EdsonHaruo_M.pdf: 7225528 bytes, checksum: 18ef99acba609c719adac9b690048969 (MD5) Previous issue date: 2012 / Resumo: Inúmeros trabalhos de pesquisa tem sido feitos em torno de um processo de soldagem por atrito conhecido por FSW, ou Friction Stir Welding. A proposta deste trabalho é determinar o efeito das tensões residuais resultantes de tal processo sobre a propagação de trincas na região próxima à junta soldada. Este efeito é considerado calculando-se fatores de intensidade de tensão residual pelo uso de funções ponderadoras e pelo método de elementos finitos. Técnicas numéricas e equações de taxa de propagação modificadas são empregadas para determinar a vida residual em fadiga de sólidos com trincas que atravessam transversalmente a região da solda. É abordado e aplicado um meio de determinar uma curva de tensão residual longitudinal a partir de uma curva de fatores de intensidade de tensão residual. Finalmente, o ensaio cut compliance é apresentado como uma técnica experimental eficaz na determinação de uma curva de fatores de intensidade de tensão residual. A aplicação de tal método exige o conhecimento prévio ou o cálculo de funções de influência. Demonstra-se que o método de elementos finitos é eficaz na determinação de tais funções / Abstract: Numerous research papers have been published on a process known as friction stir welding or FSW. The purpose of this work is to determine the effect of residual stresses resulting from such process on the propagation of a crack near the weld. This effect is taken into account by calculating residual stress intensity factors using weight functions and finite elements. Numerical techniques and crack propagation rate equations are employed to determine residual fatigue life of solids with cracks that traverse across the weld region. A way to determine a longitudinal residual stress curve from a residual stress intensity factor curve is discussed and applied in this work. Finally, the cut compliance method is presented as an effective experimental technique to determine residual stress intensity factor curves. The application of such method requires calculation of influence functions. It is shown that the finite element method is effective in determining those functions / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Friction Stir Welding (FSW) was used to perform a Design of Experiment (DOE) to determine the welding parameters effects on yielding consistent mechanical properties across the length of the weld. The travel speed was varied across set forge force and RPM conditions, to find a dataset that will yield consistent mechanical properties independent of the travel speed. Six different welds were completed on two different aluminum panels, the advancing side being Aluminum alloy 2195-T8 at a thickness of .350”, with the retreating side being Aluminum alloy 2219-T851 with a gauge thickness of .360”. A Left-hand Right-hand self-reacting pin tool was used for each weld. The mechanical properties of interest are the Ultimate Tensile Strength, Yield Strength, Elasticity and Hardness. The strengths were evaluated by tensile testing, with the Elasticity being measure post break. Specimens were then polished where macrograph and micrograph analysis was completed. Micro-hardness testing was then completed on the weld nuggets.

Le friction stir welding (FSW) est un procédé de soudage inventé en 1991 par l’institut de soudure anglais, le TWI. Celui-ci suscite un vif intérêt de la part de l’industrie aéronautique par sa capacité de souder les alliages d’aluminium de la série 2XXX et 7XXX, à durcissement structural, réputés pratiquement insoudables. Ce procédé étant relativement récent, il fait encore sujet de recherches actives. Ce travail a pour objectif de prévoir le profil de dureté d’un joint soudé par FSW d’un alliage d’aluminium, le 2024 T3. Cet alliage étant à durcissement structural, il est nécessaire de prévoir l’influence de la température sur l’évolution de la précipitation au cours du procédé pour en déduire sa limite d’élasticité. L’estimation du champ de température durant le régime stationnaire du procédé s’appuie sur des travaux internes au centre SMS. La prévision de la précipitation au cours du soudage est effectuée à l’aide de deux modèles. Le premier modèle, à base d’équivalence temps–températures, est une proposition d’extension aux alliages d’aluminium sous-revenu du modèle de Myhr & Grong (1991) établi dans le cas des alliages d’aluminium sur-revenu. Le deuxième modèle s’appuie sur une discrétisation de la distribution des rayons des précipités, suivant le schéma numérique de Kampmann et Wagner (1983), pour calculer ensuite son évolution. Bien que le premier modèle permette de prévoir l’évolution de la dureté au cours de recuits isothermes, les profils de dureté simulés ne sont pas en accord avec les profils expérimentaux. Seul le deuxième modèle permet une prévision raisonnable de la microstructure, en accord avec les mesures réalisées dans la thèse de Genevois (2004), et des profils de dureté proches des résultats expérimentaux. Finalement, une expression analytique en fonction des paramètres microstructuraux du flux de chaleur lors d’un essai de calorimétrie différentielle (DSC) a été établie. Celle-ci donne la possibilité de simuler un essai de DSC, et de vérifier ainsi la cohérence entre les grandeurs thermodynamiques et cinétiques introduites dans le deuxième modèle de précipitation. / Friction stir welding (FSW) is a recent welding process invented by The Welding Institute (TWI). It is particularly interesting for the aeronautical sector due to its capacity to weld 2XXX and 7XXX age-hardening aluminium alloys, which were previously considered unweldable. This relatively new process is currently the subject of active research. This work aims to simulate the hardness profile of an AA2024-T3 friction stir weld. AA2024-T3 is an age hardening aluminium alloy, so it is necessary to predict the effect of temperature on the evolution of precipitation during the process to deduce its yield strength. An estimation of the temperature field during the stationary regime relies on internal work of the SMS centre. Precipitate evolution during welding is simulated using two models. The first one, based on the isokinetic strength, is an extension to under-aged aluminium alloys of the Myhr & Grong model (1991) established for the overaged aluminium alloy. The second one, based on the Kampmann and Wagner (1983) numerical framework discretizes the distribution of the precipitate radius to deduce its evolution. Though the first model can predict the hardness evolution during isothermal treatments, the simulated profiles do not match the experimental ones. Only the second one can predict reasonably well the microstructures in agreement with the observations described in the thesis of Genevois (2004) and also with hardness profiles close to the experimental ones. An analytical expression for the heat flux during a differential scanning calorimetry experiment has been established as a function of microstructural parameters. This gives one the possibility to simulate a DSC experiment and to validate the coherency between thermodynamical and kinetic quantities, as introduced in the second precipitation model.

Friction Stir Processing (FSP) has the potential for locally enhancing the properties of Al-Si alloy castings, for demanding applications within the automotive industry. In this thesis, the effect of FSP has been examined on three different cast Al-Si alloys:i) A Hypoeutectic Al-8.9wt%Si Alloyii) A Hypereutectic Al-12.1wt%Si Alloyiii) A Hypereutectic Al-12.1wt%Si-2.4wt%Ni AlloyThe influence of different processing parameters has been investigated at a fundamental level. Image analysis of particle size distributions and growth method of tessellation were used to quantify the level of particle refinement and the homogeneity of the second phase spatial distribution. Stop-action experiments were also carried out, to allow the microstructural changes around the tool during FSP to be studied. Two computer models have been explored, in order to predict the temperature distribution and the material flow behaviour. Furthermore, the stability of the microstructure of the friction stir processed material was studied after being heat treated at elevated temperatures. The changes in particle size and grain structure were examined, hardness measurements were taken across the PZ, and tensile testing were carried out at room and elevated temperatures.After FSP, the microstructure of the cast Al-Si alloys was greatly refined. However, differences in microstructure have been observed throughout the PZ, which tended to be better refined and distributed on the advancing side, than the retreating side of the PZ. Changing the processing parameters also influenced the size and spatial distribution of the second phase particles. By studying the changes in microstructure around the tool from the stop-action experiments, and comparing the results to the thermal distribution and material flow behaviour predicted by the computer models, it has been shown that the flow stress, pitch, and temperature of processing, all needed to be considered, when determining the effects that FSP have on the microstructure. FSP caused very little changes to the hardness of the material, while tensile properties were greatly improved, due to the elimination of porosity and refinement of large flawed particles. In terms of the stability of the microstructure after FSP, particle coarsening and abnormal grain growth has been observed during high temperatures heat treatment. Furthermore, the Al2Cu phase was found to dissolve into solid solution at elevated temperatures, so GPZs and solute clustering can then develop within the alloy during natural ageing.

Friction stir welding (FSW) is a well recognised method for joining aluminium alloys and other engineering materials at a temperature below their melting point. However, the microstructure of the alloys may be modified during the welding process due to frictional heat and severe plastic deformation. In this study, the microstructures of friction stir welded AA5754-H111 and AA5083-O aluminium alloys have been investigated using optical microscopy, transmission and scanning electron microscopy equipped with electron backscatter diffraction (EBSD) and energy dispersive x-ray (EDX) facilities. Typical weld zones introduced by FSW were observed. Further, a joint line remnant flaw (JLR) within the thermomechanical affected zone (TMAZ) of the welds was also revealed. The formation of the JLR is attributed to dispersion of the magnesium rich oxides within the joining line.The effect of the modified alloy microstructure on the corrosion behaviour of the welds has been investigated by corrosion susceptibility testing and ex-situ SEM examination. Both parent alloys and welds showed good exfoliation and intergranular corrosion resistance (IGC). However, severe localized corrosion was observed at joint line remnant and the weld root.Reduced hardness was recorded in the heat affected zone (HAZ) of AA5754-H111 aluminium alloy weldment. This is attributed to the heat generated during welding that led to grain coarsening. In contrast, slightly increased hardness was recorded within the TMAZ. This was related to the grain refinement as a result of the recrystallization process that took place due to the effect of the thermal cycle and the plastic deformation. Little hardness change was recorded within AA5083-O aluminium alloy weldment. This was attributed to the effect of the alloy temper condition.Thermal simulation of the service environment of the friction stir welded alloys was conducted to assess the resistance to sensitization of welds. After exposure of the welded AA5754 and AA5083 alloys at 50, 70 and 170°C for prolonged time, the resistance of the AA5083 alloy weld to the IGC drastically decreased owing to the precipitation of magnesium rich particles known as β-phase at the grain boundaries. On the contrary, the resistance of the AA5754 alloy weld to IGC remained after the thermal exposure. Thus, the level of Mg content in Al-Mg alloys plays an important role in determining the corrosion characteristics of the alloys. The precipitation of Mg rich particles (β-phase) on the grain boundary is the determining factor for the resistance of the AA5xxx alloys to IGC owing to the difference in the electrode potentials between the β-phase and the grain interior, which leads to the generation of microgalvanic cells and selective dissolution of the grain boundary.

Corrosion Protection and Microstructure of Dissimilar Materials. A thesis submitted to The University of Manchester for the degree of Doctor of Philosophy by Uyime, Donatus on the 30th of July, 2015.Investigations on the micro- and macro-galvanic corrosion mechanisms in un-coupled AA2024-T3 alloys, AA2024-T3 coupled with mild steel (with and without the influence of cadmium and under varying solution temperatures), dissimilar friction stir welds of AA5083-O and AA6082-T6 alloys and a friction stir welded AA7018 alloy have been carried out. Selected methods of preventing and / or minimising the investigated corrosion phenomena were also investigated. The investigation of the corrosion behaviour of the uncoupled AA2024-T3 alloy revealed that there are two distinct stages of polarization during the galvanostatic polarization of AA2024T3 alloy in de-aerated 3.5% NaCl solution. From the first stage, the relationships between the pitting incubation time, pitting potential and applied current density for AA2024T3 alloy in the de-aerated condition were established. Whilst studying the in situ corrosion phenomena on the uncoupled AA2024-T3 alloy using the scanning vibrating electrode technique (SVET),three distinct stages in the variation of the recorded current density values with time were revealed. Attempts were made to correlate these stages with the corrosion behaviour of the alloy. The study of the galvanic interactions between AA2024-T3 and mild steel revealed that AA2024-T3 is anodic to mild steel at room temperature, but polarity reversal of the couple starts (from a temperature as low as 35 oC upwards) when the couple is introduced into the solution above ambient temperature. Importantly, AA2024-T3 is clearly cathodic to mild steel at 60 oC, although with very low measured galvanic current values. Cadmium coating (at ambient temperature) on the mild steel reduced the galvanic corrosion of the couple by as much as 20 µA/cm2 because of the formation of a CdO/Cd(OH)2 layer on mild steel. In the study of the dissimilar friction stir welds of AA5083-O and AA6082-T6 alloys, it was observed that material flows (pushes but does not mix) more from the advancing side into the retreating side and that the mixture of materials is far from complete. Two welding speeds were compared; the welding speeds have no clear influence on the microhardness, but affected the mixing proportions in the flow arm and in the nugget stem. The faster welding speed resulted in increased susceptibility to corrosion because of the reduced tool rotation per weld length for heat generation and the mixing of materials. The heat affected zones of both alloys and the transition regions between the AA5083-O alloy and the AA6082-T6 alloy rich zones have been identified to be the regions that are most susceptible to corrosion. Anodizing the weld in order to minimise corrosion showed that the AA5083-O alloy rich zones materials, in the weld, oxidizes more during anodizing compared with the AA6082-T6 alloy rich zones. Sputtering deposition prior to anodizing, promotes the formation of a uniform oxide film across the entire weld zones and prevents the boundary dissolution that occurs when the dissimilar weld of AA5083-O and AA6082-T6 alloys is anodized in 4 M H2SO4 solution at 15 V at ambient temperature. The investigation of the corrosion susceptible regions in friction stir welded AA7018 alloy, which was based on the use of ISO 11846 immersion test and the potentiodynamic polarization technique in naturally aerated 3.5 % NaCl solution, revealed intergranular, crystallographic and second phase particle influenced mode of attack. The heat affected zone was found to be the most susceptible to corrosion.

Friction stir welding is an advanced welding process that is being investigated for use in many different industries. One area that has been investigated for its application is in healing critical nuclear reactor components that are developing cracks. However, friction stir welding is a complicated process and it is difficult to predict what the final properties of a set of welding parameters will be. This thesis sets forth a method using finite element analysis and a random forest model to accurately predict hardness in the welding nugget after processing. The finite element analysis code used and ALE formulation that enabled an Eulerian approach to modeling. Hardness is used as the property to estimate because of its relationship to tensile strength and grain size. The input parameters to the random forest model are temperature, cooling rate, strain rate, and RPM. Two welding parameter sets were used to train the model. The method was found to have a high level of accuracy as measured by R^2, but had greater difficulty in predicting the parameter set with higher RPM.

In Sweden spent nuclear fuel is planned to be placed 500 m down in the bedrock. The spent nuclear fuel will be contained in copper canisters. The reason behind the selection of copper is its thermodynamic stability against corrosion in the depository. The copper will be exposed to mechanical loading and will be plastically deformed due to creep. The canisters will be sealed by friction stir welding. Since the canisters have to survive intact for many thousands of years, the properties of the welds are critical. Oxygen free P-doped copper (Cu-OFP) is selected for its excellent creep ductility properties and corrosion resistance. In this thesis work creep ductility behavior of friction stir welded copper chosen at different areas of the weld is evaluated by using the test slow strain rate tensile test. Samples are chosen at different weld areas namely weld, cross weld and HAZ. A sum of 21 specimens is tested. These tests are achieved at three various strain rates and each rate are carried out at three different temperatures. The strain rates used for tests are 1e-4, 3e-6 and 1e-7 [1/s]. The samples are strained until rupture, 20% and 5% of the gauge length. Yield strength and tensile strength are usually decreasing with increasing temperature and at higher temperature the material can be easily deformed. Few strange behaviors are also observed for the samples from HAZ areas at strain rate 1e-7[1/s]. The experimental results are justified by using the Knock-Mecking model. The parametersand ω were evaluated by curve fitting method.

The Swedish model for final disposal of nuclear fuel waste is based on copper canisters as a corrosion barrier with an inner pressure holding insert of cast iron. One of the methods to seal the copper canister is to use the Friction Stir Welding (FSW), a method invented by The Welding Institute (TWI). This work has been focused on characterisation of the FSW joints, and modelling of the process, both analytically and numerically. The first simulations were based on Rosenthal’s analytical medium plate model. The model is simple to use, but has limitations. Finite element models were developed, initially with a two-dimensional geometry. Due to the requirements of describing both the heat flow and the tool movement, three-dimensional models were developed. These models take into account heat transfer, material flow, and continuum mechanics. The geometries of the models are based on the simulation experiments carried out at TWI and at Swedish Nuclear Fuel Waste and Management Co (SKB). Temperature distribution, material flow and their effects on the thermal expansion were predicted for a full-scale canister and lid. The steady state solutions have been compared with temperature measurements, showing good agreement. Microstructure and hardness profiles have been investigated by optical microscope, Scanning Electron Microscope (SEM), Electron Back Scatter Diffraction (EBSD) and Rockwell hardness measurements. EBSD visualisation has been used to determine the grain size distribution and the appearance of twins and misorientation within grains. The orientation maps show a fine uniform equiaxed grain structure. The root of the weld exhibits the smallest grains and many annealing twins. This may be due to deformation after recrystallisation. The appearance of the nugget and the grain size depends on the position of the weld. A large difference can be seen both in hardness and grain size between the start of the weld and when the steady state is reached. / QC 20101207

Combinations of different materials are increasingly used in the modern engineering structures. The driving forces of this trend are rising fuel costs, global warming, customer demands and strict emission standards. Engineers and industries are forced to improve fuel economy and cut emissions by introducing newly design engines and lightweighting of structural components. The use of lightweight materials in the structures has proved successful to solve these problems in many industries especially automobile and aerospace. However, industry still lacks knowledge how to manufacture components from polymeric materials in combination with metals where significant differences exist in properties. This thesis aims to demonstrate and generate the methodology and guidelines for hybrid joining of aluminium alloys to thermoplastics using friction stir welding. The developed technique was identified, optimized and evaluated from experimental data, metallography and mechanical characterization. The success of the technique is assessed by benchmarking with recent literatures. In this work, lap joints between aluminium alloys (AA5754, AA6111) and thermoplastics (PP, PPS) were produced by the friction stir welding technique. The specimens were joined with the friction stir welding tools under as-received conditions. Metallic chips were generated and merged with the molten thermoplastic to form a joint under the influence of the rotating and translating tool. The effects of process parameters such as rotational speed, translational speed and distance to backing were analyzed and discussed. The investigation found joint strength was dominated by mechanical interlocking between the stir zone and the aluminium sheet. The results also show that the joint strength is of the same order of magnitude as for other alternative joining techniques in the literature. / <p>QC 20150908</p>