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Although carbon nanotubes/aluminum (CNT/Al) composites are promising materials in the production of structural components, their mechanical behavior under overaging conditions has not been considered. In this paper the effect of CNTs on the microstructural and mechanical behavior of a 2024 aluminum alloy (Al2024) synthesized by mechanical alloying (MA) and powder metallurgy routes is discussed, as well as the effect of aging heat treatments at different temperatures and aging times. The mechanical behavior of composites was screened by hardness measurements as function of aging time. After 96 h of aging time, composites showed mechanical stability in their hardness performance. Images from transmission electron microscopy showed that the mechanical stability of composites was due to a homogeneous dispersion of CNTs in the aluminum matrix and a subsequent alteration in the kinetics of precipitation is due to their presence in the aluminum matrix. Even though strengthening precipitation took place during aging, this was not the main strengthening mechanism observed in composites. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanotube/2024 aluminum alloy (CNT/Al2024) composites were fabricated with a combination of mechanical alloying (MA) and powder metallurgy routes. Composites were microstructurally and mechanically evaluated at sintering condition. A homogeneous dispersion of CNTs in the Al matrix was observed by a field emission scanning electron microscopy. High-resolution transmission electron microscopy confirmed not only the presence of well dispersed CNTs but also needle-like shape aluminum carbide (Al4C3) crystals in the Al matrix. The formation of Al4C3 was suggested as the interaction between the outer shells of CNTs and the Al matrix during MA process in which crystallization took place after the sintering process. The mechanical behavior of composites was evaluated by Vickers microhardness measurements indicating a significant improvement in hardness as function of the CNT content. This improvement was associated to a homogeneous dispersion of CNTs and the presence of Al4C3 in the aluminum alloy matrix. [Copyright &y& Elsevier]

Abstract: The wear behavior of the 2024 aluminum alloy and its composites was evaluated through a pin-on-disk system. For this purpose the aluminum alloy was reinforced by carbon nanotubes dispersion produced by milling process. The nanotubes dispersion was carried out using a high energy mill for a fixed milling time. Milled powders were cold consolidated, sintered and then microstructurally and mechanically evaluated. The wear behavior of the alloy and its composites was evaluated considering the different nanotube contents under several abrasive conditions. The composites with higher nanotube concentration (5.0wt%) displayed an improved wear resistance in all cases evaluated in this work. [Copyright &y& Elsevier]

Abstract: In the present work, the 2024 aluminum alloy (Al2024) alloy has been produced by mechanical alloying (MA). The alloy was then strengthened by dispersion of carbon nanotubes (CNTs) during different times. Thus, the effect of CNTs concentration and milling time on the microstructure of the Al2024-CNTs composites was studied. The results show a homogeneous dispersion of CNTs into the Al-matrix phase by mechanical milling (MM). It was observed that the increment in the milling time, for a fixed amount of CNTs, causes a reduction of the particle size of powders resulting from MA. The finest particle size was obtained at 20h of milling. These observations were confirmed by scanning and transmission electron microscopy. After 10h of milling, Cu, Mg and other alloying elements constituting the Al2024 alloy, form a solid solution and only some remnant Mn particles were observed but not detected by X-ray diffraction. [Copyright &y& Elsevier]

The effect of graphite, CeO 2 and nanohybrid CeO 2 -graphite on an Al–Mg–Si system (6063 alloys) was studied in this paper. Such alloy was reinforced using mechanical milling, followed by a conventional sintering process. Studies for structure, microstructure, and mechanical properties were carried out through X-ray diffraction, electron microscopy, and compression and Vickers microhardness testing. Results showed that the milling process enables homogeneous dispersion of the different reinforcement materials in the Al–Mg–Si matrix. The best performance, concerning reinforcement capacity and microhardness, was obtained with samples reinforced with graphite. The mechanisms involved in enhancing the mechanical properties were active and latent. The first includes grain-size refinement and strengthening by dispersion of a second phase, and the second is related to thermal mismatch. [Display omitted] • The Gr, CeO 2 , and nanohybrid CeO 2 -Gr reinforcements were homogeneously dispersed. • The reinforcements containing Gr presented the formation of Al 4 C 3 during sintering. • The CeO 2 presented a partial reduction into Ce 7 O 12 during sintering. • The reinforcements containing Gr showed the best mechanical response. • The active and latent strengthening mechanisms enhanced the mechanical properties. [ABSTRACT FROM AUTHOR]

Highlights: [•] Al7075–graphite composites were fabricated by mechanical alloying and hot extrusion. [•] Mechanical properties are enhanced as function of graphite content and milling time. [•] The strengthening is due to grain refining, Al4C3 and increased dislocation density. [ABSTRACT FROM AUTHOR]