The low-cycle fatigue (LCF) life of the extruded aluminum alloy 6061-T6 (AA6061-T6) AM2 matting connection system was analyzed through 3D finite element modeling in conjunction with the plasticity-damage (DMG) and multi-stage fatigue (MSF) material models. The connection was modeled in ABAQUS Explicit based on the real-world boundary conditions of AM2 matting. The DMG-MSF user-defined material model characterized the low-cycle fatigue damage evolution within the microstructure of the extruded AA6061-T6 connection and utilized the maximum effective strain amplitude to predict the life of each stage of the fatigue process. It was determined that a constant displacement range of 15.17 mm generated an effective strain amplitude of 6.8E-03 mm/mm and a predicted total fatigue life within 1% to the laboratory- and full-scale data at approximately 1,122 cycles. The LCF characterization of the connection system allows for a significant reduction in laboratory- and full-scale testing for future design improvements.

Submitted by Rafael Santana (rafael.silvasantana@ufpe.br) on 2017-04-19T18:29:57Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação CAMILA ALBUQUERQUE FERNANDES 2016.pdf: 2707069 bytes, checksum: 1af5a8e892dd9aa2682c79f98c6cde09 (MD5) / Made available in DSpace on 2017-04-19T18:29:57Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação CAMILA ALBUQUERQUE FERNANDES 2016.pdf: 2707069 bytes, checksum: 1af5a8e892dd9aa2682c79f98c6cde09 (MD5) Previous issue date: 2016-07-29 / Solda a Ponto por Fricção (Friction Spot Welding – FSpW) é um processo relativamente novo de soldagem desenvolvido e patenteado pelo GKSS na Alemanha, que visa complementar e/ou substituir tecnologias de uniões de soldagem convencionais. Essa nova tecnologia de soldagem se dá pela união no estado sólido, onde duas ou mais chapas são unidas através da transferência de energia térmica e mecânica que é gerada pela rotação da ferramenta. O presente trabalho visou avaliar a aplicabilidade da união da liga de alumínio 6061-T6 pela técnica de Solda a Ponto por Fricção. Essas soldas foram produzidas em configuração de sobreposição utilizando condições de soldagens variadas, por meio de diferentes combinações de velocidade de rotação, profundidade de penetração e velocidade de penetração; os quais foram estabelecidos através de uma análise estatística, utilizando como ferramenta o Box-Behnken. A integridade da junta soldada foi avaliada através dos efeitos dos parâmetros de processo, na geometria e na microestrutura da junta, e também no desempenho mecânico. Realizou-se também a otimização do processo de soldagem e um estudo sobre o comportamento de fratura das soldas submetidas a um esforço de cisalhamento. Os resultados mostraram que a melhor combinação de parâmetros foi encontrada na condição de soldagem: 130 rpm, 4,0 mm/s e 1,4 mm, com um valor médio de resistência ao cisalhamento de 6243,29 N, com boa reprodutibilidade. O botão da solda é constituído por três elementos geométricos que se mostraram inerentes ao processo: cunha, união principal e união secundária. Estes elementos mostraram possuir forte influência sobre o desempenho mecânico. / Friction Spot Welding (FSpW) is a relatively new welding process patented by GKSS in Germany. This new welding technology is given by the joining in a solid state, in which two or more plates are joined by thermal and mechanical energy transfer that is generated by the rotation of the welding tool. The aim of this work is to study the integrity of the welds of AA6061-T6, by the FSpW process. These welds were produced in an overlapping configuration using different welding conditions, through different combinations of rotational speed, depth of penetration and penetration speed, which were set through a statistical approach using the Box-Behnken. The integrity of the welded joint was evaluated by the effects of process parameters on geometry and microstructure of the joint, and also in the mechanical performance. It was also performed the optimization of the welding process and a brief study on the fracture behavior of the welds subjected to a shear stress. The results showed that the best combination of parameters was found in the welding condition: 130 rpm 4.0 mm / s and 1.4 mm with an average value of the shear strength of 6243.29 N, with good reproducibility. The metallurgical investigation revealed three geometric elements that are inherent to the process: primary union and secondary union and hook. These elements were shown to have strong influence on the mechanical performance.

Yes / In this study, a new double pin tool was utilized for the development of AA6061/316 stainless steel reinforced composite by employing the friction stir processing technique for the first time. The microstructure, hardness, tensile, tribological, and corrosion behaviors of the fabricated composites were investigated and comparative assessments were made with the results obtained from the single-pin tool. The results showed that particle-matrix reaction did not occur in the composites irrespective of the nature of the tool profile. The double-pin tool outstandingly boosted the grain refinement (7.01–5.78 μm), particle fragmentation, and distribution within the Al matrix due to the additional pin-assisted plastic deformation, high straining, dynamic recrystallization, and Zener pinning effects. The double-pin tool improved the microhardness (127–141 HV), tensile strength (162–233 MPa), and corrosion resistance of the composite with respect to the single-pin tool counterparts. The replacement of the single pin tool with a double pin tool diminished the specific wear rate (0.38–0.22 mm3/Nm) of the composite. The double-pin tool has a favourable impact on the structure, mechanical, and corrosion behaviours of the AA6061/316 stainless steel reinforced composite. It is thus recommended for composite development.

Yes / In this study, the modified friction stir clinching process was successfully utilized to weld the AA7075-T6 to AA6061-T6 aluminum alloys. The approach of this study was to appraise the influence of the stirring time (6, 12, and 18 s) on the metallurgical and mechanical behavior of the welded samples. The microstructural study demonstrated that stirring time significantly affected joint properties and material flow, which can be ascribed to the discrepancy in the properties of the Al alloys used in this study. Void, local melting and defect-free joints were produced under the stirring times of 6 s, 18 s, and 12 s respectively. It was found that tensile/shear strength increased significantly from 63.5 MPa to 109 MPa as the stirring time increased from 6 s to 12 s, while a further increase in the stirring time to 18 s significantly decreased the joint's strength to 76.1 MPa. The observed failed samples showed that stirring time did not influence fracture mode.

This thesis systematically investigates the effects of a recently developed modified ageing procedure of aluminium alloys, termed the T6I6 temper, on the microstructural development and mechanical properties of the Al ??? Mg ??? Si - Cu alloy 6061. For the T6I6 temper, a conventional single stage T6 temper is interrupted by an ageing period at a reduced temperature (65??C) to facilitate secondary precipitation, before resuming the final ageing at the temperature of the initial T6 treatment. The T6I6 temper was found to cause simultaneous increases in tensile properties, hardness, and toughness as compared with 6061 T6. Al ??? Mg ??? Si ??? Cu alloys are medium strength alloys widely used in the automotive industry and their further improvement is underpinned by stringent demands for weight reduction placed on the transportation industry in recent years. The potential for further improvement of the mechanical properties was found in the control of secondary precipitation that may take place even in some fully aged alloys when exposed to reduced temperatures. The overall improvement in the mechanical properties of 6061 T6I6 was attributed to the formation of finer and more densely dispersed precipitates in the final microstructure. The refinement of precipitates was facilitated by control of the precipitation processes and gradual evolution of the microstructure throughout each stage of the T6I6 treatment. The results indicated that the concentration and the chemical environment of the vacancies controlled the precipitation processes in this alloy. Findings also show that the proportion of the different precipitate phases present in the final microstructure, as well as the amount of the solute in these precipitates, can be controlled and modified utilizing secondary precipitation. A number of analytical techniques were used in this study. The evolution of the microstructure was studied using Transmission Electron Microscopy (TEM), High Resolution TEM (HRTEM) and Three Dimensional Atom Probe (3DAP). Vacancy-solute interactions were studied using Positron Annihilation Lifetime Spectroscopy (PALS) and 3DAP. The distribution of the solute was studied using 3DAP and Nuclear Magnetic Resonance (NMR). Differential Scanning Calorimetry (DSC) was used to identify precipitation reactions and to determine the stability of vacancy-associated aggregates.

This thesis systematically investigates the effects of a recently developed modified ageing procedure of aluminium alloys, termed the T6I6 temper, on the microstructural development and mechanical properties of the Al ??? Mg ??? Si - Cu alloy 6061. For the T6I6 temper, a conventional single stage T6 temper is interrupted by an ageing period at a reduced temperature (65??C) to facilitate secondary precipitation, before resuming the final ageing at the temperature of the initial T6 treatment. The T6I6 temper was found to cause simultaneous increases in tensile properties, hardness, and toughness as compared with 6061 T6. Al ??? Mg ??? Si ??? Cu alloys are medium strength alloys widely used in the automotive industry and their further improvement is underpinned by stringent demands for weight reduction placed on the transportation industry in recent years. The potential for further improvement of the mechanical properties was found in the control of secondary precipitation that may take place even in some fully aged alloys when exposed to reduced temperatures. The overall improvement in the mechanical properties of 6061 T6I6 was attributed to the formation of finer and more densely dispersed precipitates in the final microstructure. The refinement of precipitates was facilitated by control of the precipitation processes and gradual evolution of the microstructure throughout each stage of the T6I6 treatment. The results indicated that the concentration and the chemical environment of the vacancies controlled the precipitation processes in this alloy. Findings also show that the proportion of the different precipitate phases present in the final microstructure, as well as the amount of the solute in these precipitates, can be controlled and modified utilizing secondary precipitation. A number of analytical techniques were used in this study. The evolution of the microstructure was studied using Transmission Electron Microscopy (TEM), High Resolution TEM (HRTEM) and Three Dimensional Atom Probe (3DAP). Vacancy-solute interactions were studied using Positron Annihilation Lifetime Spectroscopy (PALS) and 3DAP. The distribution of the solute was studied using 3DAP and Nuclear Magnetic Resonance (NMR). Differential Scanning Calorimetry (DSC) was used to identify precipitation reactions and to determine the stability of vacancy-associated aggregates.