Strengthening in nanostructured 2024 aluminum alloy and its composites containing carbon nanotubes

The ultrafine-grained 2024 aluminum alloy (A2024) and A2024 matrix composites containing carbon nanotubes (CNTs) are developed. Three strengthening strategies of grain boundary hardening, age hardening and hardening by CNTs are employed. First, grain size of A2024 is effectively reduced using a ball-milling technique and A2024 with a grain size of 100 nm exhibits a yield stress of ∼560 MPa, exhibiting a well agreement with the Hall–Petch relation. CNTs also have a great effect for strengthening. The A2024 matrix composite containing 3 vol.% CNTs shows a yield stress of ∼780 MPa with 2% tensile elongation to failure. Hardness is further increased after aging. The nanostructured composite shows its peak hardness after 4 h of aging because the refined grain boundaries and CNTs act as a pathway for diffusion of atoms with stimulating the aging process. The composite in the present study has great potential for application as structural materials in industry.