The linear friction welding process is currently commercially used solely to produce titanium alloy aeroengine bladed disks (blisks). The process can, however, be potentially used to produce welds in non-aeroengine materials for non-aeroengine applications. The aim of this thesis was therefore to demonstrate the capabilities of the process to join materials not commonly used in the aeroengine industry and to develop understanding of the process. The focus of this thesis has been on the linear friction welding of 316L stainless steel and the linear friction welding of dissimilar materials: aluminium to copper, aluminium to magnesium and aluminium to steel. For all of these studies it was seen that weld line and near weld line microstructure could be altered by the use of different welding parameters. This property of linear friction welding was used to advantage to optimise microstructures in dissimilar welds. Intermetallic formation is usually a major challenge to the achievement of welds with good mechanical properties, and for work in this thesis welding parameters were optimised to allow welds with limited intermetallic formation. The welding of 316L and the dissimilar welding of aluminium to copper proved viable. For the welding of 316L and aluminium to copper, fracture during tensile testing occurred in the parent material (aluminium parent material for aluminium to copper). The welding of aluminium to magnesium and aluminium to steel showed promising results, with weld strength comparable to the aluminium parent material for aluminium to steel and comparable to the parent materials in O temper for aluminium to magnesium. However, repeatability of mechanical properties was poor for these dissimilar welds, which would be a significant barrier to commercial exploitation. Further work needs to be conducted to improve repeatability. Weld microstructures were characterised using optical and scanning electron microscopy as well as electron backscatter diffraction and X-ray diffraction techniques.

Joining of dissimilar metals is a process that is of interest in many fields, especially the automotive industry where lightweighting of the body structure is important. However, creating strong joints between dissimilar metals can be challenging. Friction bit joining (FBJ) is a solid-state method that uses a consumable bit to create a strong joint between dissimilar metals such as aluminum and steel. The purpose of this research is to gain understanding of how adjusting FBJ parameters affects the heating and pressure at the weld interface using a modeling approach, in order to better understand the bonding process. The questions guiding this research are: (1) What is the effect of spindle speed, plunge rate, and plunge depth on joint strength? (2) Can the proposed model be developed with enough fidelity to correlate the effect of these parameters on joint strength, within 10%? (3) What is the effect of the simulated vertical load profile on heating at the interface? (4) Does the load profile/heating relationship correlate to experimental joint strength to within 10%? A design of experiments approach found that the effect of spindle speed on joint strength is significant. Plunge rate did not have a significant effect, but the interaction between plunge rate and spindle speed was significant. A model was created, and multiple simulations were run to study these interactions. Initial simulations were run based on the input parameters used for the experiments. The simulation data was used to run a full second order regression was run which found that spindle speed had a significant effect on the experimental Z load. The data also revealed that spindle speed and plunge rate have a strong correlation between bonded area and temperature. Simulated versus experimental Z loads have a good correlation. Experimental bonded area had a slight correlation to joint strength trending in the correct direction. The shape of the simulated cross section did not fully match the experimental cross sections but was reasonable. Simulated bonded area and experimental bonded area also have a positive correlation. Despite some weaknesses, the current model does appear to be predictive enough that it can provide insight into other FBJ design configurations and material combinations in terms of temperature profiles and welding loads.

No description available.

No description available.

Um dos mais críticos problemas encontrados na união de materiais distintos é a formação de tensões residuais, que ocorre principalmente pelo fato desses materiais possuírem coeficientes de expansão térmica e condutividades térmicas diferentes. Neste trabalho foi estudada a técnica de soldagem laser entre o aço carbono AISI 1010 e o aço inoxidável AISI 304. Os materiais foram unidos por solda autógena de topo com um laser de Nd:YAG contínuo. O principal objetivo do estudo foi a identificação da influência dos parâmetros de soldagem, pela análise das tensões residuais na zona termicamente afetada (ZTA). Foi executado um planejamento fatorial de três fatores a dois níveis com uma réplica, em que foram variadas a potência, a velocidade de soldagem e a posição focal do feixe laser. Na superfície da amostra foram realizadas medidas de tensão residual pela técnica de difração de raios X, para estudar sua variação em função dos parâmetros investigados. O método do furo cego foi também utilizado para avaliar a tensão residual ao longo da profundidade das amostras até a profundidade de 1 mm. Além das medidas de tensão residual, os cordões de solda foram avaliados por microscopia óptica e eletrônica de varredura (MEV), que tiveram como objetivos determinar a geometria do cordão e mudanças na microestrutura, também foram feitas medidas de microdureza Vickers para se avaliar a extensão da ZTA. Para se avaliar as propriedades mecânicas da união foram realizados ensaios de tração e fadiga. O software MINITAB 15 foi utilizado para a análise das tensões residuais nas diferentes profundidades da ZTA obtidas pelo método do furo cego. Foi utilizada também a regressão estatística baseada nas diferentes influências da entrada e combinação dos fatores na tensão residual geradas nessa união. Os resultados indicam que o desenvolvimento de modelos pode prever as respostas satisfatoriamente e fornecer aos usuários um guia para definir os melhores parâmetros de união. / The dissimilar materials union has the residual stress formation as one of the most critical problems, which occurs mainly because these materials have both different thermal expansion coefficients and thermal conductivities. In this study, it was investigated the laser welding technique between steels, AISI 1010 and AISI 304. The materials were joined by butt autogenous welding with a continuous Nd:YAG laser. The main objective was to identify the welding parameters influence by the residual stresses analysis in the heat affected zone (HAZ). It was executed a factorial design with three-factor at two levels with a replica, which were varied power, welding speed and focal position of the laser beam. Residual stress measurements by the diffraction of X-rays were performed on the sample surface, to study their variation as a function of the parameters investigated. The blind hole method was also used to evaluate the residual stress along the samples depth, up to depth of 1mm. Besides residual stress measurement, weld seams were evaluated by optical and scanned electron microscopy, which were aimed to determine the weld geometry and changes in the microstructure. It was also made Vickers hardness measurements to evaluate the extent of HAZ. To evaluate the mechanical properties of the union were performed tensile and fatigue test. The MINITAB 15 software was used to analyze the residual stresses obtained by the blind hole method at different depths of the HAZ. It was also used statistical regression based on both the influences different and the combination of this input factors, in the residual stress of union. The results indicate that the models can satisfactorily predict the responses and provide users a guide to better define the welding parameters.

O presente trabalho estuda uniões entre chapas de aço DP600 e chapas das ligas de alumínio AA 6181–T4 e AA 5754–H22, obtidas através do processo Friction Spot Welding (FSpW). A soldagem de materiais dissimilares é um dos grandes desafios para a engenharia, pois as propriedades de distintos materiais são muito diferentes na maioria das vezes, o que dificulta a realização deste tipo de união pelos métodos convencionais de soldagem com fusão. O processo FSpW requer menos energia que os processos de soldagem convencionais, não produz fumos, radiação ou resíduos. Permite obter a união de materiais no estado sólido, sendo, portanto potencialmente indicado para uniões dissimilares. Por ser um processo muito mais “limpo” que os usados convencionalmente, pode contribuir significativamente com uma grande preocupação mundial que é a sustentabilidade. A influência de um revestimento galvanizado nas chapas de aço para a qualidade das uniões resultantes foi avaliada realizando-se as operações de soldagem com as chapas de aço nas condições com e sem a camada galvanizada. O método estatístico de Taguchi foi utilizado para definir os parâmetros de soldagem que maximizassem a resistência das juntas para cada condição de ensaio, sendo a qualidade das juntas obtidas definida pela resistência da união ao ensaio de cisalhamento. Durante a soldagem, a temperatura em pontos específicos foi adquirida e, posteriormente, as juntas foram submetidas à análise metalográfica e de composição química por EDS. A partir da análise das macro e microestruturas dos corpos de prova com melhor resistência ao cisalhamento, foi possível associar diferentes parâmetros de processo e mecanismos de união para cada tipo de junta. O estudo comprovou a possibilidade de obtenção de uniões dissimilares entre o aço e as duas ligas de alumínio através do processo FSpW, especialmente quando utilizou-se o aço com a camada galvanizada que apresentou modo de união mais eficaz. / This work aims at the study of welding DP600 steel to AA6181-T4 and AA5754-H22 aluminum alloys plates by Friction Spot Welding (FSpW). Welding of dissimilar materials is a great challenge for engineering due to the diverse properties of different materials, that difficult welding by conventional methods of fusion. FSpW is a joining method that requires lower energy than conventional welding processes and produces no hazard gases or radiation. It allows solid state joining that is potentially indicated to dissimilar materials joining, and contributes significantly to sustainability, because the process can be considered “cleaner” that those used conventionally. The influence of the galvanized layer on the joint performance with the steel plates on was tested using steel plates with and without this coating. The Taguchi statistic method was employed to define the welding process parameters that produce higher shear stress resistance to each test condition, so the welding joints quality was defined based on the union resistance to shear. During the welding operation the temperature at given positions was acquired and the resulting joints were submitted to metallographic and chemical composition analysis. From the analysis of specimen that showed best stress test performance to each joint condition, it was possible to associate different process parameters and joint mechanisms to each condition. The study demonstrates the feasibility of joining the steel to both aluminum alloys using FSpW. The best shear test results were obtained with the presence of a galvanized layer.

O presente trabalho estuda uniões entre chapas de aço DP600 e chapas das ligas de alumínio AA 6181–T4 e AA 5754–H22, obtidas através do processo Friction Spot Welding (FSpW). A soldagem de materiais dissimilares é um dos grandes desafios para a engenharia, pois as propriedades de distintos materiais são muito diferentes na maioria das vezes, o que dificulta a realização deste tipo de união pelos métodos convencionais de soldagem com fusão. O processo FSpW requer menos energia que os processos de soldagem convencionais, não produz fumos, radiação ou resíduos. Permite obter a união de materiais no estado sólido, sendo, portanto potencialmente indicado para uniões dissimilares. Por ser um processo muito mais “limpo” que os usados convencionalmente, pode contribuir significativamente com uma grande preocupação mundial que é a sustentabilidade. A influência de um revestimento galvanizado nas chapas de aço para a qualidade das uniões resultantes foi avaliada realizando-se as operações de soldagem com as chapas de aço nas condições com e sem a camada galvanizada. O método estatístico de Taguchi foi utilizado para definir os parâmetros de soldagem que maximizassem a resistência das juntas para cada condição de ensaio, sendo a qualidade das juntas obtidas definida pela resistência da união ao ensaio de cisalhamento. Durante a soldagem, a temperatura em pontos específicos foi adquirida e, posteriormente, as juntas foram submetidas à análise metalográfica e de composição química por EDS. A partir da análise das macro e microestruturas dos corpos de prova com melhor resistência ao cisalhamento, foi possível associar diferentes parâmetros de processo e mecanismos de união para cada tipo de junta. O estudo comprovou a possibilidade de obtenção de uniões dissimilares entre o aço e as duas ligas de alumínio através do processo FSpW, especialmente quando utilizou-se o aço com a camada galvanizada que apresentou modo de união mais eficaz. / This work aims at the study of welding DP600 steel to AA6181-T4 and AA5754-H22 aluminum alloys plates by Friction Spot Welding (FSpW). Welding of dissimilar materials is a great challenge for engineering due to the diverse properties of different materials, that difficult welding by conventional methods of fusion. FSpW is a joining method that requires lower energy than conventional welding processes and produces no hazard gases or radiation. It allows solid state joining that is potentially indicated to dissimilar materials joining, and contributes significantly to sustainability, because the process can be considered “cleaner” that those used conventionally. The influence of the galvanized layer on the joint performance with the steel plates on was tested using steel plates with and without this coating. The Taguchi statistic method was employed to define the welding process parameters that produce higher shear stress resistance to each test condition, so the welding joints quality was defined based on the union resistance to shear. During the welding operation the temperature at given positions was acquired and the resulting joints were submitted to metallographic and chemical composition analysis. From the analysis of specimen that showed best stress test performance to each joint condition, it was possible to associate different process parameters and joint mechanisms to each condition. The study demonstrates the feasibility of joining the steel to both aluminum alloys using FSpW. The best shear test results were obtained with the presence of a galvanized layer.

O presente trabalho estuda uniões entre chapas de aço DP600 e chapas das ligas de alumínio AA 6181–T4 e AA 5754–H22, obtidas através do processo Friction Spot Welding (FSpW). A soldagem de materiais dissimilares é um dos grandes desafios para a engenharia, pois as propriedades de distintos materiais são muito diferentes na maioria das vezes, o que dificulta a realização deste tipo de união pelos métodos convencionais de soldagem com fusão. O processo FSpW requer menos energia que os processos de soldagem convencionais, não produz fumos, radiação ou resíduos. Permite obter a união de materiais no estado sólido, sendo, portanto potencialmente indicado para uniões dissimilares. Por ser um processo muito mais “limpo” que os usados convencionalmente, pode contribuir significativamente com uma grande preocupação mundial que é a sustentabilidade. A influência de um revestimento galvanizado nas chapas de aço para a qualidade das uniões resultantes foi avaliada realizando-se as operações de soldagem com as chapas de aço nas condições com e sem a camada galvanizada. O método estatístico de Taguchi foi utilizado para definir os parâmetros de soldagem que maximizassem a resistência das juntas para cada condição de ensaio, sendo a qualidade das juntas obtidas definida pela resistência da união ao ensaio de cisalhamento. Durante a soldagem, a temperatura em pontos específicos foi adquirida e, posteriormente, as juntas foram submetidas à análise metalográfica e de composição química por EDS. A partir da análise das macro e microestruturas dos corpos de prova com melhor resistência ao cisalhamento, foi possível associar diferentes parâmetros de processo e mecanismos de união para cada tipo de junta. O estudo comprovou a possibilidade de obtenção de uniões dissimilares entre o aço e as duas ligas de alumínio através do processo FSpW, especialmente quando utilizou-se o aço com a camada galvanizada que apresentou modo de união mais eficaz. / This work aims at the study of welding DP600 steel to AA6181-T4 and AA5754-H22 aluminum alloys plates by Friction Spot Welding (FSpW). Welding of dissimilar materials is a great challenge for engineering due to the diverse properties of different materials, that difficult welding by conventional methods of fusion. FSpW is a joining method that requires lower energy than conventional welding processes and produces no hazard gases or radiation. It allows solid state joining that is potentially indicated to dissimilar materials joining, and contributes significantly to sustainability, because the process can be considered “cleaner” that those used conventionally. The influence of the galvanized layer on the joint performance with the steel plates on was tested using steel plates with and without this coating. The Taguchi statistic method was employed to define the welding process parameters that produce higher shear stress resistance to each test condition, so the welding joints quality was defined based on the union resistance to shear. During the welding operation the temperature at given positions was acquired and the resulting joints were submitted to metallographic and chemical composition analysis. From the analysis of specimen that showed best stress test performance to each joint condition, it was possible to associate different process parameters and joint mechanisms to each condition. The study demonstrates the feasibility of joining the steel to both aluminum alloys using FSpW. The best shear test results were obtained with the presence of a galvanized layer.

Um dos mais críticos problemas encontrados na união de materiais distintos é a formação de tensões residuais, que ocorre principalmente pelo fato desses materiais possuírem coeficientes de expansão térmica e condutividades térmicas diferentes. Neste trabalho foi estudada a técnica de soldagem laser entre o aço carbono AISI 1010 e o aço inoxidável AISI 304. Os materiais foram unidos por solda autógena de topo com um laser de Nd:YAG contínuo. O principal objetivo do estudo foi a identificação da influência dos parâmetros de soldagem, pela análise das tensões residuais na zona termicamente afetada (ZTA). Foi executado um planejamento fatorial de três fatores a dois níveis com uma réplica, em que foram variadas a potência, a velocidade de soldagem e a posição focal do feixe laser. Na superfície da amostra foram realizadas medidas de tensão residual pela técnica de difração de raios X, para estudar sua variação em função dos parâmetros investigados. O método do furo cego foi também utilizado para avaliar a tensão residual ao longo da profundidade das amostras até a profundidade de 1 mm. Além das medidas de tensão residual, os cordões de solda foram avaliados por microscopia óptica e eletrônica de varredura (MEV), que tiveram como objetivos determinar a geometria do cordão e mudanças na microestrutura, também foram feitas medidas de microdureza Vickers para se avaliar a extensão da ZTA. Para se avaliar as propriedades mecânicas da união foram realizados ensaios de tração e fadiga. O software MINITAB 15 foi utilizado para a análise das tensões residuais nas diferentes profundidades da ZTA obtidas pelo método do furo cego. Foi utilizada também a regressão estatística baseada nas diferentes influências da entrada e combinação dos fatores na tensão residual geradas nessa união. Os resultados indicam que o desenvolvimento de modelos pode prever as respostas satisfatoriamente e fornecer aos usuários um guia para definir os melhores parâmetros de união. / The dissimilar materials union has the residual stress formation as one of the most critical problems, which occurs mainly because these materials have both different thermal expansion coefficients and thermal conductivities. In this study, it was investigated the laser welding technique between steels, AISI 1010 and AISI 304. The materials were joined by butt autogenous welding with a continuous Nd:YAG laser. The main objective was to identify the welding parameters influence by the residual stresses analysis in the heat affected zone (HAZ). It was executed a factorial design with three-factor at two levels with a replica, which were varied power, welding speed and focal position of the laser beam. Residual stress measurements by the diffraction of X-rays were performed on the sample surface, to study their variation as a function of the parameters investigated. The blind hole method was also used to evaluate the residual stress along the samples depth, up to depth of 1mm. Besides residual stress measurement, weld seams were evaluated by optical and scanned electron microscopy, which were aimed to determine the weld geometry and changes in the microstructure. It was also made Vickers hardness measurements to evaluate the extent of HAZ. To evaluate the mechanical properties of the union were performed tensile and fatigue test. The MINITAB 15 software was used to analyze the residual stresses obtained by the blind hole method at different depths of the HAZ. It was also used statistical regression based on both the influences different and the combination of this input factors, in the residual stress of union. The results indicate that the models can satisfactorily predict the responses and provide users a guide to better define the welding parameters.

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.