Synthesis of Carbon Nanotube-Reinforced Al2024 Matrix Nanocomposite Using Flake Powder Metallurgy Method

Abstract

In current work, the flake powder metallurgy method was applied to achieve the uniform dispersion of carbon nanotubes (CNTs) within the Al2024 powder. For this purpose, the flake morphology of Al2024 powder with suitable diameter-to-thickness ratio (D/t = 85) was obtained after ball milling for 4 hours at 250 rpm and ball-to-powder ratio = 10. Then, the surface of matrix was modified by a hydrophilic polymer [polyvinyl alcohol (PVA)] to obtain the sufficient –OH group on its surface. Additionally, the refluxing of CNTs in nitric acid was performed at 393 K (120 °C) for 6 hours to functionalize the reinforcement by –COOH agent. After preparation of initial materials, the Al2024–1.5 wt pct CNTs suspension was stirred in a slurry at pH 3 until the color was changed in steady state from ink-like to transparent at pH 5. The hydrogen bonding was formed between the –OH groups of PVA coated Al2024 and –COOH groups of functionalized MWCNTs during the mixing step. Also, the temporary polarity could be considered between H+ and $${{\rm{C}}_{12}}{{\rm{H}}_{25}}{\rm{SO}}_4^ -$$ ions on the surface of constituents, which led to improvement in the CNT distribution due to the changing of suspension pH. Consequently, the homogenous dispersion of CNTs in Al2024 flaky powders resulted in a chemical reaction of constituents without any destructive effects of mechanical forces. The morphological changes of Al2024 powders were studied by scanning electron microscopy (SEM), and surface treatments were evaluated by Fourier transform infrared and Raman spectroscopies. The dispersion of nanocomposite powder was investigated through field emission SEM. Also, X-ray diffraction analysis was used to investigate the initial Al2024 powder and formed phases after the ball milling process.