Hot deformation behavior and microstructure evolution of carbon nanotube/7055Al composite

In this study, carbon nanotube (CNT) reinforced 7055Al composite was fabricated by high energy ball milling combined with powder metallurgy. The as hot-pressed composite had an inhomogeneous microstructure composed of coarse grains without CNTs and fine grains with uniformly dispersed CNTs. Processing maps were established and the hot deformation behavior as well as the microstructure evolution during deformation was investigated. It was indicated that the power dissipation efficiency of the composite was relatively lower at higher deformation temperature or lower strain rate. Abnormal grain growth (AGG) and cracking occurred when the composite was deformed at high temperature with low strain rate. A few of CNTs were embedded into coarse grains as AGG occurred, and the micro-cracks formed at the boundaries between the coarse and the fine grained zones. The cracking mechanism was considered as the stress concentration caused by the dragging effect of CNTs, and the reduced critical stress required for pore nucleation due to AGG at the boundaries between the coarse and the fine grained zones. (C) 2020 Elsevier B.V. All rights reserved.