Age hardening behavior of carbon nanotube reinforced aluminum nanocomposites

In the present work, age hardening behavior of CNT reinforced Al6061 and Al2124 nanocomposites, prepared by ball milling and spark plasma sintering, was investigated. The effect of CNT content, annealing time and temperature on the age hardening behavior of the nanocomposites was evaluated and compared to the monolithic alloys prepared and age hardened under the same conditions. It was found that CNTs have a negative influence on the age hardening of the alloys. The alloys displayed standard age hardening behavior i.e. a sharp increase in hardness during initial aging followed by a steady decrease in hardness. Whereas the nanocomposites did not only display initial softening during aging but also showed reduced age hardening efficiency. The hardening efficiency was found to decrease with increasing CNT content. The complicated behavior of nanocomposites was explained in terms of dislocation recovery, large thermal mismatch between matrix and CNTs and bulk microstructure of the composites.