Heat treatment behavior and strengthening mechanisms of CNT/6061A1 composites fabricated by flake powder metallurgy

The carbon nanotubes reinforced 6061A1 composites (CNT/6061A1) with CNTs uniformly dispersed were fabricated by flake powder metallurgy process. The mechanical properties of composites, with and without artificial heat -treatment, were compared to the unreinforced 6061A1 alloy. It was found that higher content of oxygen was introduced with increasing CNTs and consumed the magnesium element, which had a negative effect on the precipitation strengthening mechanism. Thus, the strength improvement of CNT/6061A1 composites by heat treatment was less significant than the monolithic 6061A1 alloy. However, the T6-aged CNT/6061A1 composites still exhibited enhanced yield strength and ultimate tensile strength than the monolithic 6061A1 alloy. This was attributed to the synergistic strengthening of multi-mechanisms, such as precipitation strengthening, grain refinement strengthening, load transfer behavior of CNTs and especially, CNT-induced back stress strengthening and the strain hardening. As results, the aged CNT/6061A1 composites with 1.5 wt% CNTs had balanced tensile strength of 469 MPa and uniform elongation of 6%.