Superplastic deformation behavior of carbon nanotube reinforced 7055 Al alloy composites

The superplastic deformation behavior of a carbon nanotube reinforced high-strength aluminium alloy matrix composite (CNT/7055Al) was investigated at temperatures ranging from 300 to 425 degrees C and strain rates ranging from 10(-2) to 5 s(-1). A maximum elongation of 125% was observed for the as-extruded CNT/7055Al at 400 degrees C and a high strain rate of 5 s(-1). After a T6 treatment (solution and artificial aging treatment), the CNT/7055Al achieved a higher elongation of 153% at 400 degrees C and 5 s(-1) due to the fewer second-phase particles. The strain rate sensitivity and activation energy were determined to be 0.2 and 171 kJ/mol, respectively. Combined with microstructural observation, it was demonstrated that the main deformation mechanism for the CNT/7055Al was lattice diffusion controlled dislocation climb. Further, it was found that CNTs played a negative role in the superplastic deformation, which could be attributed to the large aspect ratio of CNTs and strong CNT-Al interface bonding.