Effect of milling time and CNT concentration on hardness of CNT/Al2024 composites produced by mechanical alloying

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.

► The 2024 aluminum alloy was reinforced by CNTs by mechanical alloying process.
► Composites were microstructural and mechanically evaluated after sintering condition.
► The greater the CNT concentration, the greater the hardness of the composites.
► Higher hardness in composites is achieved at 20 h of milling.
► The formation of Al4C3 does not present a direct relationship with the milling time.