Development and implementation of strategies for the incorporation of reinforcing elements in aluminium alloys by solid state processing

Dissertação para obtenção do Grau de Mestre em Engenharia MecânicaThis investigation aimed to study new surface processing strategies to produce reinforced surface metal matrix composites by Friction Stir Processing. The first consisted on pre-placing reinforcing particles over the surface, while the second used consumables drilled holes filled with reinforcing particles. Each strategy was investigated using an electric current in a process under patenting. Aluminium AA5083-H111 plates were used as base material. Silicon carbide and alumina particles with median sizes of 35 and 45 μm, respectively, were used. Pre deposition of reinforcing particles proved to be more effective than the use of consumable tools packed with particles. The last ones produced coatings with a non homogeneous distribution and poor bonding between the substrate and the reinforcing coating. The pre deposition of alumina produced a higher extension and depth of reinforced layer and an increase in hardness of 60%, while silicon carbide produced an increase in hardness of 300 %, though in a smaller extension and depth than alumina under the same processing conditions. Using the electric current a significant raise of 500% and 40% was observed in extension and depth respectively, but hardness decreased by 10 %

Granting Sensorial Properties to Metal Parts through Friction Stir Processing

The authors would like also to thank to Micronsense-Metrologia Industrial (Leiria, Portugal) for the μCT analysis. The authors would also like to thank Prof. Catarina Santos for granting access to the MicroLab - Electron Microscopy Laboratory (Instituto Superior Técnico) for the SEM analyses.Structural Health Monitoring systems assess the part's current condition. This can be performed with a monitoring system comprising sensors, on the surface or embedded, in the monitored parts. However, surface sensors are subject to damage, and embedding the sensors may result in a weakened part. An innovative Self-Sensing Material and its manufacturing process were developed and are presented herein. As proof of concept, Barium Titanate particles were introduced and dispersed into an AA5083-H111 part by Friction Stir Processing (FSP). The particles’ distribution and concentration was evaluated by a set of characterization techniques, demonstrating that greater concentrations, grant enhanced sensitivity to the material. The use of FSP and the embedded particles improved the part’s mechanical behaviour in the processed zone. The sensorial properties were assessed and the response to a set of dynamic loads was measured, being coherent with the solicitations provided. The developed self-sensing material revealed an electrical sensitivity of 12.0 × 10-4 uV/MPa.publishersversionpublishe

Preliminary study on the production of functionally graded materials by friction stir processing

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia MecânicaAn investigation was carried out to evaluate the potential application of Friction Stir Processing (FSP) to produce Functionally Graded Materials (FGM‟s). Friction stir processed materials can be considered as FGM‟s since the localized microstructural modification results in a gradual property modification. Therefore, to enhance hardness and ductility at specific superficial levels, surface layers of processed material were produced by multiple-pass FSP with an overlap ratio of 0.5. Overlapping was done on the advancing (AS) and retreating sides (RS) to study potential differences on the resulting mechanical properties. It was observed that processing in these two conditions led to different surface topography, since overlapping by the advancing side resulted in a wave-like surface profile. The mechanisms involved in FSP also led to its exploitation for the production of particle-reinforced Metal Matrix Composite (MMC) materials, as the severe plastic deformation produced during the process promotes the dispersion of the particles within the matrix. An investigation was conducted in order to produce aluminium based functionally graded MMCs reinforced by SiC ceramic particles with median size of 118.8, 37.4 and 12.3 micron. AA5083 aluminium alloy plates in the H111 and partially annealed conditions were processed. Several strategies for reinforcement were investigated and its influence on the particle distribution and homogeneity. The most promising results were achieved when the pin fully overlapped the groove. SiC fraction area analysis revealed two orthogonal gradients. Since FSP was used as a surface processing technique, the magnitude of the microstructural effects generated by the tool gradually decreases along the depth of the processed material. A second gradient was generated parallel to the bead surface due to the asymmetric nature of material flow around the tool. The use of smaller sized particles led to more homogeneous composite layers and smother gradients. Tool wear was very significant, proving that SiC reinforcement is not the most suitable method to produce FGM‟s

Comparison of mechanical performance between friction-stir spot welded and adhesive bonded joints

The main objective of this study is to compare the mechanical strength of friction stir spot welded (FSSW) joints and adhesive bonded single lap ones. The present study aims to compare the morphology and strength of welded and adhesive bonded joints. The welded joints were done by friction stir spot welding and the adhesive bonded ones by the use of the adhesive Araldite 420 A/B. The produced joints were subjected to morphology and microstructure analyzes, microhardness tests, tensile-shear tests and local strain analyzes. The welded joints have higher strength than adhesive-bonded joints. However, this difference is insignificant, around 5%, which is covered by the standard deviation. The connection by FSSW proves to be an alternative to adhesive bonded joints, offering the same strength, but with the connection at isolated points, inducing local stress concentration

Hybrid manufacturing processes for fusion welding and friction stir welding of aerospace grade aluminum alloys

Friction stir welding and processing can provide for joints in aerospace grade aluminum alloys that have preferable material properties as compared to fusion welding techniques. Aerospace grade aluminum alloys such as AA2024-T3 and AA7075-T6 are considered non-weldable by traditional fusion welding techniques. Improved mechanical properties over previously used techniques are usually preferable for aerospace applications. Therefore, by combining traditional fusion welding and friction stir processing techniques, it could be plausible to create more difficult geometries in manufactured parts instead of using traditional techniques. While this combination of fusion welding and friction stir processing is not a new technology, its introduction to aerospace grade aluminum alloys as well as non-weldable alloys, is new. This is brought about by a lowered required clamping force required by adding a fusion weld before a friction stir processing technique. The changes in properties associated with joining techniques include: microstructural changes, changes in hardness, tensile strength, and corrosion resistance. This thesis illustrates these changes for the non-weldable AA2024-T351 and AA7075-T651 as well as the weldable alloy AA5052-H32. The microhardness, tensile strength and corrosion resistance of the four processing states: base material, fusion welded material, friction stir welded material, and friction stir processed fusion welded material is studied. The plausibility of this hybrid process for the three different materials is characterized, as well as plausible applications for this joining technique --Abstract, page iii

Desenvolvimento da tecnologia Friction Stir Channelling - estudo da influência da base no processamento de ligas de alumínio

A presente dissertação visa contribuir para o desenvolvimento da tecnologia Friction Stir Channelling, que é um processo no estado sólido que permite, através da fricção linear, produzir canais contínuos no interior de uma peça maciça numa única passagem e com a trajetória que se pretender. O intuito específico desta investigação foi avaliar a influência da base (local onde a chapa a processar é fixada) no processo. Para tal optou-se por utilizar duas bases com características térmicas distintas. Sendo uma delas mais convencional (base de aço CK45) e que permite um fácil escoamento do calor, enquanto a outra de um material isolante (baquelite). Através da análise dos ensaios realizados e da caracterização dos canais produzidos concluiu-se que a base é um fator preponderante para que este processo possa ser realizado com sucesso, pois os ensaios realizados com a base isolante (baquelite) permitiram concluir que o calor excessivo no processo pode impedir a formação de canais. Nesses ensaios foram observadas diversas contraindicações para a utilização deste tipo de base, desde canais não estanques, a canais completamente abertos e instáveis, por não ser possível manter o processo estacionário, verificando-se um aumento constante da temperatura. Deste modo, desenvolveu-se e produziu-se uma base de cobre refrigerada, com o intuito de se retirar dependência dos parâmetros do processo no fabrico do canal. Assim sendo, o que se espera é que se possa estabilizar a temperatura do processo através da utilização de uma base refrigerada e que os parâmetros do processo possam apenas fazer variar a geometria do canal

Forming effects on high-cycle fatigue in an aluminum sheet structure using the Ottosen-Stenström-Ristinmaa model

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