Fabrication and consolidation behavior of Al 6061 nanocomposite powders reinforced by multi-walled carbon nanotubes

The composite behavior of an Al 6061 nanocrystalline matrix reinforced with different weight percentages (0, 0.5, 1.0, 1.5 and 2.0 wt.%) of multi-walled carbon nanotubes (MWCNTs) produced by mechanical alloying (MA) with a milling time of 30 h was investigated. MWCNTs were added during the last 2 h of milling to avoid structural damage during MA. The milled powders were consolidated by cold uni-axial compaction followed by sintering at different temperatures (450 °C, 525 °C and 600 °C) under a reducing atmosphere (N2) to evaluate the materialsʹ sinterability. The structure of the MWCNTs was evaluated by Raman spectroscopy of as-received pure MWCNTs, Al 6061-2 wt.% MWCNT nanocomposite powder after 30 h MA and sintered samples of Al 6061-1 wt.% MWCNTs & Al 6061-2 wt.% MWCNTs. The crystallite size and lattice parameter of the composites were examined. The relative density, compressibility, green compressive strength, sinterability and Vickers hardness of the composites were also examined. The effects of MWCNTs as reinforcement on the consolidation behavior of the nanocrystalline matrix were studied using the Heckel, Panelli and Ambrosio Filho and Ge equations. The fabricated composites exhibited high Vickers hardness of 76 HV (818 MPa), which is approximately three times higher than that of microcrystalline Al 6061. However, because of MWCNTs that were added during the last 2 h of milling, higher hardness values were obtained in this investigation.