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
