Effect of processing parameters on the cyclic behaviour of aluminium friction stir welded to spark plasma sintered aluminium matrix composites with bimodal micro-and nano-sized reinforcing alumina particles

Understanding the cyclic behaviour of Alumina reinforced Aluminium composites (Al-A2O3) was of critical importance, for their further application in the different industrial sectors. The present study is focussing on the cyclic behaviour of the Al-Alumina nanocomposite produced through the combination of spark plasma sintering (SPS) method and friction stir welding (FSW). The added Alumina with total content of 10% is the combination of nano and micro-sized particles and its ratio differ for each sample. The microstructure of the SPSed samples is characterized using optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). The microstructure of the processed composite samples is characterized and its mechanical behaviour is studied. Microstructural studies showed that nano sized particles of Alumina were mostly distributed along the grain boundaries and inside the grains, while micron-sized ones mostly settled on the grain boundaries. In addition, the hardness and tensile properties of the produced samples are analysed concerning the reinforcement size and the percentage of nanoparticles addition. The obtained results reveal that the mechanical and fatigue properties of the nanocomposite materials mainly depend on the material properties at the initial stage and the applied conditions of friction stir welding such as rotating speed and movement speed. The facture surface of the nanocomposites revealed a combined ductile–brittle fracture mode with finer dimples with emphasis on the pronounced role of nano-metric dispersoids.