## 2 Materials and Methods  
Al and nanocomposite samples were produced through a powder metallurgy route where the aluminum powder was dispersed/mixed to 1.00 vol.% of multi-walled carbon nanotubes. Both the aluminum powders from Goodfellow Cambridge Ltd. (Huntingdon, UK) and the carbon nanotubes from Fibermax Nanocomposites Ltd. (London, UK) were fully characterized with advanced techniques, such as SEM, TEM, HRTEM and RAMAN in previous works [12; 13; 14; 15; 16; 17; 18; 19]. In these works, morphology and microstructure were studied to know the powders to a great extent and to evaluate the damage of the CNT during the nanocomposite production. The characterization of the aluminum powders was performed using SEM images and EBSD analysis using a Thermo Fisher Scientific QUANTA 400 FEG SEM (Thermo Fisher Scientific, Hillsboro, OR, USA) with an EBSD detector TSL-EDAX EBSD Unit (EDAX Inc. (Ametek), Mahwah, NJ, USA). The metallic particle analysis was also performed using dynamic light scattering (DLS) in a Laser Coulter LS230 (Beckman Coulter, Inc., Brea, CA, USA). The morphology of CNTs was observed by SEM and by high-resolution TEM (HRTEM, JEOL Ltd., Tokyo, Japan). The carbon nanotubes were characterized using the same SEM equipment as mentioned before, especially with a JEOL high-resolution electron microscope (JEOL Ltd., Tokyo, Japan). Since the strengthening effect and, consequently, the mechanical properties of the nanocomposite are directly associated with the dispersion of the reinforcement in the matrix, the dispersion/mixture technique was ultrasonication. This was based on previous works [12; 13; 14; 15] being the most efficient method compared with others. The dispersion and mixture of the Al and CNTs (1.00 vol.%) were performed in a single step using ultrasonication and isopropanol for 15 min using 20-400 rpm. These mixtures were then cold-pressed with 300 MPa using a metallic mould with the geometry of the tensile test specimen. The tensile test specimen geometry is described elsewhere [14]. The compact was sintered at 640 \({}^{\circ}\)C for 90 min under a high vacuum to avoid oxidation. The tensile test was performed with a velocity of 0.2 mm/s, using Shimadzu EZ Test equipment (Shimadzu Corporation, Kyoto, Japan), and four samples of each, nanocomposite and aluminium matrix, were tested. It is important to mention that to enable the comparison between them, both Al and Al/CNTs powders were ultrasonicated, cold-pressed and sintered under the same conditions. Nanoindentation tests using Micro Materials-NanoTest equipment with a Berkovich diamond indenter (NanoTest, Micro Materials Limited, Wrexham, UK) were conducted to investigate the hardness and reduced Young's modulus. The depth-sensing indentation test was performed in load control mode up to a maximum load of 20 mN. Indentation matrixes formed by rows and columns were defined. Further microstructural analysis and microhardness tests were performed on the fractured tensile specimen. The fracture surface was analyzed using the digital microscope Leica DVM6 and Leica LAS X software (Leica Microsystems, Wetzlar, Germany) and by SEM. After tensile testing, this characterization was conducted in Al and nanocomposite for comparison behavior. For the microstructural characterization, since the electron backscattered technique (EBSD) is a very powerful characterization technique for investigation deformation behaviors, the top view of fractured tensile samples was analyzed by high-resolution SEM (Thermo Fisher Scientific QUANTA 400 FEG SEM, Thermo Fisher Scientific, Hillsboro, OR, USA), coupled to an EBSD detector TSL-EDAX EBSD Unit (EDAX Inc. (Ametek), Mahwah, NJ, USA). However, to avoid dubious results and indexing errors, the obtained data were submitted to a routine clean-up where the grain tolerance angle was determined to be 15\({}^{\circ}\) and the need of 2 points minimum to define a grain.