Grain refinement and superplastic behavior of carbon nanotube reinforced aluminum alloy composite processed by cold rolling

The carbon nanotube reinforced aluminum matrix composite (CNT/6061Al) fabricated by flake powder metallurgy was cold rolled to reduce grain size, and was examined by high temperature tensile experiments within temperature from 325 to 450 °C and strain rate from 4.17E−2 to 2.09 s-1 to explore the effect of grain refinement on the superplastic deformation behavior. The average grain size was reduced from 580 nm to 300 nm with better homogeneity after cold rolling, and elongation to failure at 400 °C and 4.17E−1 s-1 was improved by 40% compared to that without cold rolling. The temperature of 375 °C and intermediate strain rate turned out to be appropriate deformation conditions for the refined microstructure, in which both large elongation to failure and uniform elongation was obtained. Stress exponent was changed to 2 and activation energy was determined to be 76.7 kJ/mol, indicating grain boundary sliding was the main deformation mechanism.