Laser welding of metals and alloys is extensively used in industry due to its advantages of controlled heating, narrow weld bead, low heat affected zone (HAZ) and its ability to weld a wide range of metals and dissimilar metals. Laser welding of dissimilar metals such as carbon steels and stainless steel is still a challenging task, particularly due to the formation of brittle phases in the weld, martensitic formation in the HAZ and solidification cracking in the fusion zone. These issues can significantly deteriorate the strength of the welded joint. The aim of this work is to investigate the fundamental phenomena that occur inside the dissimilar weld zone and their effect on weld quality. In order to establish the key process variables, an initial study concentrated on the effect of different laser process parameters on dissimilar weld quality. In the second part of the work, a comprehensive study was performed to understand and subsequently control the alloying composition in laser dissimilar welding of austenitic stainless steel and low carbon steel. A dissimilar weld that is predominantly austenitic and homogeneous was obtained by controlling the melt pool dynamics through specific point energy and beam alignment. The significance of dilution and alloying elements on joint strength was established. A coupled CFD and FEM numerical model was developed to assist in understanding the melt pool dynamics and transportation processes of alloying elements. The model has been validated by a series of laser welding experiments using various levels of specific point energy. The laser welding characteristics in terms of geometric dimensions, surface morphology, alloying concentration, and dilution, were compared, and it is concluded that the specific point energy and laser beam position are the key parameters that can be controlled to obtain a weld bead with characteristics most suitable for industrial applications. In the third part of the work, a comparative study was performed to understand the significance of cooling rate, and alloying composition on the microstructure and phase structure of the dissimilar weld zone. Results show that the HAZ within the high carbon steel has significantly higher hardness than the weld area, which severely undermines the weld quality. A new heat treatment strategy was proposed based on the results of the numerical simulation, and it is shown to control the brittle phase formation in HAZ of high carbon steel. A series of experiments was performed to verify the developed thermo-metallurgical FEA model and a good qualitative agreement of the predicted martensitic phase distribution is shown to exist. Although this work is presented in the context of dissimilar laser welding of mild steel to stainless steel, the concept is applicable to any dissimilar fusion welding process.

Dissimilar metals joining have been used in many industry fields for various applications due to their technique and beneficial advantages, such as aluminum-steel and magnesium-steel joints for reducing automobile weight, aluminum-copper joint for reducing material cost in electrical components, steel-copper joints for usage in nuclear power plant, etc. The challenges in achieving dissimilar joints are as below. (1) Big difference in physical properties such as melting point and coefficient of thermal expansion led to residual stress and defects. (2) The miscibility issues resulted in either brittle intermetallic compound layer at the welded interface for miscible combinations (such as, aluminum-steel, aluminum-copper, aluminum-titanium, etc.) or no metallurgical bonding for immiscible combinations (such as magnesium-copper, steel-copper, etc.). For metallurgical miscible combinations, brittle intermetallic compounds formed at the welded interface created the crack initiation and propagation path during deformational tests. (3) Stress concentration appeared at the welded interface region during tensile testing due to mismatch in elastic properties of dissimilar materials. In this study, different combinations of dissimilar metals were joined with friction stir welding. Lap welding of 6022-T4 aluminum alloy/galvanized mild steel sheets and 6022-T4 aluminum alloy/DP600 steel sheets were achieved via friction stir scribe technology. The interlocking feature determining the fracture mode and join strength was optimized. Reaction layer (intermetallic compounds layer) between the dissimilar metals were investigated. Butt welding of 5083-H116 aluminum alloy/HSLA-65 steel, 2024-T4 aluminum alloy/316 stainless steel, AZ31/316 stainless steel, WE43/316 stainless steel and 110 copper/316 stainless steel were obtained by friction stir welding. The critical issues in dissimilar metals butt joining were summarized and analyzed in this study including IMC and stress concentration.

Yes / Resistance spot welding of aluminum (Al5754) to magnesium (AZ31B) alloys results in the formation of a variety of solidification microstructures and intermetallic compounds that may affect the in-service performance of the weld. This study evaluates the relationship between the welding parameters and the properties of the weld nugget that is formed, and clarifies the morphological and microstructural evolutions within the weld regions during the low-current “small-scale” resistance spot welding of Al5754 to AZ31B. The investigations included a combination of microstructural characterization and thermodynamic analysis of the weld region. The results show that the welding time and clamping force parameters have significant effects on the properties of the nugget formed. The optimal welding parameters were found to be 300 ms welding time and 800 N clamping force. Weld nuggets formed with lower welding time and clamping force were undersized and contained extensive porosity. Meanwhile, a clamping force above 800 N caused gross deformation of the test samples and the expulsion of the molten metal during the welding process. The most significant microstructural changes occurred at the weld/base metal interfaces due to the formation of Al17Mg12 and MgAl2O4 intermetallic compounds as well as significant compositional variation across the weld pool. The thermal gradient across the weld pool facilitated the formation of several microstructural transitions between equiaxed and columnar dendrites.

Yes / This study's objective was to conduct a comparative analysis and characterization of the microstructural evolution within the weld nugget for joints of AA5083-H112 and AA6061-T6 produced by friction stir spot welding (FSSW) and modified friction stir clinching (MFSC) processes. The mechanical performance of the welded joints was assessed in shear using a single lap joint. The microstructural study identified significant variation in joint microstructure and material flow due to the differences in the tool geometry and methodology used for the welding processes. The results show that the use of modified friction clinching process improves the welded joint by eliminating keyholes/hook defects leading to the formation of high-strength joints. Mechanical characterization of the welded joints indicated that the shear strength increased significantly from 78.69 MPa for the conventional FSSW to 131 MPa for the MFSC process.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / As ligas de nÃquel podem ser utilizadas na uniÃo de juntas dissimilares de aÃos carbono baixa liga. Uma das finalidades desta uniÃo à evitar a formaÃÃo de trincas induzidas pelo hidrogÃnio. Existe uma limitaÃÃo por norma que impÃe a temperatura de interpasse mÃxima de 150ÂC para soldagem com ligas de nÃquel. Contudo, a temperatura de interpasse baixa reduz a produtividade e consequentemente aumenta os custos de fabricaÃÃo. Um estudo que avalia como a temperatura de preaquecimento/interpasse na soldagem dissimilar influencia as alteraÃÃes metalÃrgicas e propriedades mecÃnicas à oportuno. Desta forma, o objetivo geral deste trabalho à avaliar o efeito do aumento da temperatura de interpasse nas alteraÃÃes metalÃrgicas e nas propriedades mecÃnicas de juntas dissimilares soldadas do aÃo ASTM A182-F22 com diferentes ligas de nÃquel. Foram realizadas soldagens MIG/MAG automÃtica em juntas do aÃo (ASTM A182-F22) utilizando diferentes ligas de nÃquel como metal de adiÃÃo e diferentes temperaturas de interpasse (35ÂC, 150ÂC e 350ÂC). A energia de soldagem foi mantida constante (1,0 kJ/mm). Baseado nos resultados obtidos o aumento da temperatura de preaquecimento tende a reduzir a fraÃÃo de precipitados, decorrente do aumento da diluiÃÃo. O coeficiente de distribuiÃÃo do Mo e Nb diminuem com o aumento do teor de ferro na solda. Isto, por sua vez, torna mais forte a segregaÃÃo destes elementos. A temperatura de interpasse tendeu a reduzir a dureza da (ZTA-GG), por conta da reduÃÃo da velocidade de resfriamento. Nos ensaios de traÃÃo os corpos de prova romperam na regiÃo referente ao metal de base. Houve uma reduÃÃo no limite de escoamento nas condiÃÃes soldadas com temperatura de 350ÂC, sendo uma possÃvel causa a precipitaÃÃo de carbonetos devido ao preaquecimento e aos multipasses. Os ensaios de Charpy-V indicaram que, de uma forma geral, o aumento da temperatura de interpasse reduziu a tenacidade na zona fundida. A energia absorvida na interface sofreu reduÃÃo com o aumento da temperatura de interpasse, decorrente do aumento da descarbonetaÃÃo. O tempo de soldagem foi reduzido de forma considerÃvel com o aumento de temperatura de interpasse, entretanto, deve-se avaliar as alteraÃÃes na ZTA e ZF. / Nickel alloys can be used to weld dissimilar joints of low alloy carbon steels. One of the purposes of this union is to avoid the formation of hydrogen induced cracking. According codes and standard there is a limitation that imposes the maximum interpass temperature at 150ÂC for welding using nickel alloys. However, the low interpass temperature reduces productivity and increases manufacturing costs. A study that evaluates effect of the preheating and interpass temperature of dissimilar welds on the metallurgical changes and mechanical properties is of great relevance. In this way, the general objective of this study is to assess the effect of interpass temperature on metallurgical changes and mechanical properties of dissimilar welded joints among ASTM A182-F22 steel and different nickel-based alloys. GMAW were carried out on joints of steel (ASTM A182-F22) using different nickel-based alloys as filler metal and different interpass temperatures (35ÂC, 150ÂC and 350ÂC). The heat input was kept constant (1.0 kJ/mm). Based on the results obtained it was observed that increasing preheating temperature there is a tends to reduce the precipitates content, because of dilution. The distribution coefficient of Mo and Nb decrease with the increase of iron content in the fusion zone, making stronger the segregation of these elements. Interpass temperature tend to reduce the HAZ hardness, due to the in cooling rate reduction caused by increase interpass temperature. In the tensile tests failure in the base metal. There was a reduction in yield strength for welds produced with 350ÂC preheat temperature, being a possible cause the precipitation of carbides due to preheating and multipasses. The Charpy-V tests indicated that, generally, the increase in interpass temperature reduced the toughness in the fusion zone. The absorbed energy by the interface dropped when interpass temperature increase. The welding time was considerably reduced with the interpass temperature increase, however, it should be to considerate changes in HAZ and fusion zone.

Com a descoberta do prÃ-sal, a PetrobrÃs està cada vez mais investindo nas exploraÃÃes de petrÃleo em Ãguas profundas e ultra profundas, o que exige um grande dispÃndio em pesquisa e desenvolvimento (P&D) na Ãrea de produÃÃo. VÃrias estruturas submarinas sÃo soldadas e possuem juntas dissimilares, como por exemplo, em conexÃo de flowlines e risers rÃgidos com os flanges presentes em manifolds e Ãrvores de natal. Esses equipamentos sÃo geralmente protegidos com proteÃÃo catÃdica galvÃnica, a qual promove a liberaÃÃo de Ãons de hidrogÃnio na superfÃcie dos materiais. Esse hidrogÃnio adsorvido migra para regiÃo da junta susceptÃveis, facilitando a propagaÃÃo de defeitos, especialmente a trinca por hidrogÃnio. De uma forma geral este trabalho possui o objetivo de avaliar os efeitos do procedimento de soldagem TIG com alimentaÃÃo de arame frio aplicado no amanteigamento dos aÃos AISI 8630M e ASTM A182 F22, considerando o uso do TTPS em diferentes condiÃÃes de soldagens de juntas dissimilares, bem como avaliar as caracterÃsticas metalÃrgicas e propriedades mecÃnicas da interface dissimilar do amanteigamento. Os materiais de base utilizados foram o AISI 8630M e o ASTM A182F22, soldados com a liga de nÃquel AWS ER NiCrMo-3 utilizando o processo TIG com alimentaÃÃo de arame frio. Em uma primeira etapa foram realizados os testes de Higuchi Convencional e Modificado, onde foram levantados os parÃmetros para aplicaÃÃo da tÃcnica da Dupla Camada. Na segunda etapa foram fabricadas juntas dissimilares com diferentes tÃcnicas de amanteigamento, utilizando os parÃmetros aprovados e reprovados nos testes de Higuchi, como tambÃm o uso ou nÃo do tratamento tÃrmico pÃs-soldagem TTPS. Em seguida, foram retiradas amostras para anÃlises dos fenÃmenos ocorridos na interface dissimilar, assim como, suas caracterÃsticas metalÃrgicas e mecÃnicas. Foi possÃvel, por meio dos testes de Higuchi Convencional e Modificado, determinar para o aÃo AISI 8630M e ASTM A 182 F22 relaÃÃes de parÃmetros de amanteigamento que, sem necessidade do uso do TTPS, resulte em zonas termicamente afetada (ZTA) bem refinadas e com durezas prÃximas da indicada por normas. As ZTA dos aÃos AISI 8630M e ASTM A182 F22 foram compostas basicamente por martensita revenida e bainita, respectivamente, onde foi observado um intenso refino de grÃos nas juntas amanteigadas com as relaÃÃes aprovadas nos testes de Higuchi Convencional e Modificado, enquanto que uma granulaÃÃo grosseira foi observada nas juntas com condiÃÃes reprovadas nos mesmos. Os ensaios de fratura indicaram que, de forma geral, os maiores valores do fator de intensidades de tensÃes (K) foram obtidos quando as pontas do entalhe estÃo localizadas dentro da ZTA. / With the discovery of the pre-salt, Petrobras is increasingly investing in oil explorations in deep water and ultra deep, which requires a large expenditure on research and development in the area of production. Several underwater structures are welded and have dissimilar joints, e.g. in connection of flow lines and risers with rigid flanges present in manifolds and Christmas trees. This equipment are generally protected with galvanic cathode protection, which promotes the release of hydrogen ions on the surface of materials. This adsorbed hydrogen migrates to the joint which region, facilitating the spread of defects, especially the fissure by hydrogen. In general this work has the objective to evaluate the effects of procedure GTAW welding with wire feed cold applied in buttering of AISI 8630M and ASTM A182 F22, considering the use of Post-Weld Heat Treatment (PWHT) in different conditions for welding dissimilar joints, as well as evaluate the metallurgical characteristics and mechanical properties of dissimilar interface of buttering. The materials used were the AISI 8630M and ASTM A182F22, welded with the nickel alloy AWS ERNiCrMo-3 using the GTAW process with cold wire feed. In a first stage were carried Conventional and Modified Higuchi Test, where were raised the parameters for application of the technique of double layer. In the second stage were manufactured dissimilar joints with different buttering techniques, using the parameters approved and disapproved Higuchi tests, as well as the use of PWHT. Then, samples were taken for analysis of the phenomena occurring in dissimilar interface, as well as, metallurgical and mechanical characteristics. It was possible, through the of Conventional and Modified Higuchi Test, determine for Steel AISI 8630M and ASTM A 182 F22 buttering parameters relationships that, without the use of PWHT, resulting in heat affected zone (HAZ) well refined and hardness close indicated by standards. The HAZ AISI 8630M steel and ASTM A182 F22 were composed basically by tempering martensite and bainite, respectively, where it was observed an intense grain refining in the buttery joints with relations adopted in Higuchi tests while a coarse granulation was observed in the joints with disapproved on the same conditions. Fracture tests indicated that, overall, the highest values of stress intensity factor (K) were obtained when the ends of the notch are located inside the HAZ.

No description available.

No / Successful joining of dissimilar metals such as Al and Mg can provide significant advantages to the automotive industry in the fabrication of vehicle bodies and other important components. This study explores dissimilar joining of Al–Mg using a resistance spot welding process to produce microstructurally sound lap joints and evaluates the impact of interlayer composition on microstructural evolution and the formation of intermetallic compounds within the weld nugget. The results indicated that mechanically sound joints can be produced, with fine equiaxed and columnar dendrites within the weld nugget. The presence of intermetallic compounds was also confirmed by the variation in the microhardness values recorded across the weld zone.

To address the concerns of simultaneously improving crash performance and fuel efficiency in the automotive industry, multi-material car bodies are becoming increasingly popular. Aluminium and steel are two materials whose properties complement each other well for this application. However, ultra-high strength steel (UHSS) and aluminium alloy is a hard-to-join material combination. In the last decades different solutions to this problem have been proposed, one of these being friction element welding (FEW). In this work, different UHSS have been joined to different aluminium alloys through the FEW equipment EJOWELD developed by EJOT. The joints have been evaluated though visual inspection, cross-section analysis, and mechanical tests. All materials could successfully be joined by the EJOWELD process.

Orientador: Vicente Afonso Ventrella / Resumo: Os aços inoxidáveis duplex e superduplex são materiais muito importantes, tanto economicamente, quanto tecnologicamente. Esses materiais possuem uma microestrutura binária, composta de 50% ferrita e 50% austenita, combinando resistência à corrosão com resistência mecânica. A soldagem a laser desses materiais faz com que ocorra desbalanceamento entra as fases da microestrutura do metal de solda, havendo formação excessiva de ferrita, e assim, perdendo suas características de resistência à corrosão e propriedades mecânicas. Este trabalho tem como objetivo aumentar a proporção de austenita no metal de solda através da soldagem à laser Nd:YAG pulsado, autógena e dissimilar, dos aços inoxidáveis superduplex UNS S32750 e superaustenítico AISI 904L, sendo este um material rico em níquel, elemento gerador de austenita. A soldagem foi feita em uma junta de topo, variando-se a taxa de sobreposição do cordão de solda em cinco condições, de 50% até 90%. A energia de pulso foi fixada em 30 J, com potência de pico de 3 kW, largura temporal de 10 ms e frequência de 3 Hz. Argônio puro foi utilizado como gás de proteção, com vazão de 15 l/min. As macrografias mostraram que a redução na taxa de sobreposição gera áreas sem solda, além de porosidades. Não observou-se formação da zona termicamente afetada macroscopicamente visível. A fratura no ensaio de tração ocorreu no metal base superaustenítico, exceto na amostra com 50% de sobreposição que fraturou no metal de solda. O ensaio de microdureza... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Duplex and super duplex stainless steels are very important materials, both economically and technologically. These materials have a binary microstructure, composed by 50% ferrite and 50% austenite, combining corrosion resistance with mechanical strength. The laser welding of these materials causes imbalance between the microstructural phases of the weld metal, with excessive ferrite formation, losing its corrosion resistance and mechanical properties. The main goal of this work is to increase the austenite proportion of the weld metal, through an autogenous and dissimilar pulsed Nd: YAG laser welding of the super duplex stainless steel UNS S32750 with the super austenitic stainless steel AISI 904L, which is a nickel-rich material. The welding was performed in a butt joint configuration, controlling the overlapping rate in five different conditions, from 50% to 90%. The pulse energy was fixed in 30 J, with peak power of 3 kW, temporal width of 10 ms and frequency of 3 Hz. Pure argon was used as protection gas, with a flow rate of 15 l/min. The macrographs showed that reducing the overlap rate generates large weld-free areas and porosities. There was no sign of macroscopically visible heat affected zone formation. The tensile test fracture occurred in the superaustenitic parent metal, except the 50% overlapping sample, that fractured in the weld metal. The Vickers microhardness test was performed, obtaining a mean of 290 HV in the weld metal. The micrographs showed poor mixing... (Complete abstract click electronic access below) / Mestre