Effect of initial state on dispersion evolution of carbon nanotubes in aluminium matrix composites during a high-energy ball milling process

In this study, a pre-mixing process was applied to assist a high-energy ball milling (HEBM) process to fabricate high-strength aluminium (Al) matrix composites reinforced with carbon nanotubes (CNTs) by powder metallurgy. Effects of initial state on the dispersion quality of CNTs in composites and resultant mechanical properties were investigated using electron microscopy and tensile testing, respectively. Results showed that after pre-mixing, raw CNT agglomerations became flattened CNT clusters, and evolved into individually dispersed CNT fragments on flaky Al powder surface after HEBM for 12 h. However, CNT clusters remained in the same HEBM process without pre-mixing. Both individual CNTs and CNT clusters were observed inside coldwelded Al particles with a prolonged milling time of 24 h. By applying pre-mixing, the reinforcing effect in CNT/Al composites increased by more than 100%. The distinct evolution processes of CNT dispersion during HEBM with different initial states have been discussed.