Unveiling the strengthening and toughening effects of copper-coated carbon nanotubes for the AlLiCu alloy matrix composite

Carbon nanotubes (CNTs) reinforced Al-Li-Cu alloy matrix composite is a promising candidate for the lightweight structural materials demanded in advanced industrial areas such as aerospace. However, how to fully exploit the combined strengthening effects of CNTs and precipitates of the Al-Li-Cu matrix is still an open issue. In the present study, the Cu coating was firstly precoated on CNTs before fabricating CNTs reinforced Al-Li-Cu alloy matrix composite. Benefiting from the Cu coating, the improved CNTs dispersion and Al-CNTs interfacial bonding was achieved, and the precipitation of Al2Cu, Al2CuLi, and Al3Li was enhanced in the AlLiCu alloy matrix, resulting in the enhanced strength-ductility synergy for Cu-coated CNTs reinforced AlLiCu alloy matrix composite. Moreover, strengthening and toughening mechanisms analyzation reveals that the Orowan strengthening of CNTs and precipitates, as well as load transfer strengthening of CNTs contribute mostly to the improved strength, while the increased ductility dominantly derives from the improved CNTs dispersion and Al-CNTs interfacial bonding, and the formation of low-density dislocation nanoregion (LDDN) in the interface area. This study not only opens up a new way for developing the AlLiCu alloy matrix composite reinforced by Cu-coated CNTs but also guides the microstructure regulation of other Al alloy matrix composites.