Study On Hot Deformation Behaviors Of CNTs/Al-Cu Composites

With the large scale production of carbon nanotubes and prices declined dramatically since 2000, CNTs reinforced aluminum composites with huge development potential has gradually become a new generation of lightweight metal matrix composites. Tremendous attention has been paid to the fabrication and mechanical properties of subsequent composites since the invention of flake powder metallurgy (flake PM) technique. To the best knowledge of the author of present study, few investigations have been conducted about the flow behavior at elevated temperature of CNTs/Al composites fabricated by flake PM.CNTs/Al-Cu composites and Al-Cu alloy are hot compressed on Gleeble 3500 thermal simulated test machine with temperature range at 300- 450℃ and strain rate range of 0.01-10.0s-1. The hot deformation behavior of CNTs/Al-Cu composites and Al-Cu alloy were discussed. Besides the hyperbolic sine equation can be used to describe the flow behavior of CNTs/Al-Cu composites and Al-Cu alloy deformed at high temperature. Processing maps of CNTs/Al-Cu composites and Al-Cu alloy at different strains were established based on the dynamic material model (DMM) by using the data obtained from the thermal compressions to optimize the processing parameters at different strains.The main conclusions are as follows:① The deformation temperature and strain rate have obvious effects on the flow characteristic. In general, the flow stress decreased with temperature at a setting strain rate; however it increased with the strain rate at a setting deformation temperature.② CNTs/Al-Cu composites fabricated by flake powder metallurgy, which are highly laminated, CNTs dispersed homogeneously along the laminated direction, result in higher effect on pinning dislocations and grain boundaries than Al2Cu particles. CNTs dispersed homogeneously along the laminated direction pinned the movable dislocations and grain boundaries, dislocations were seriously resistant, leading to the increase of dislocation movement barrier. And finally the flow stress, activation energy,etc of CNTs/Al-Cu composites are significantly higher than the Al-Cu matrix alloy.③ In this paper the hyperbolic sine equation can be used to describe the flow behavior of CNTs/Al-Cu composites and Al-Cu alloy deformed at high temperature, i.e. the hot compressive deformation processes are affected by activation energy.lt is concluded that under the experimental conditions the steady state flow stress equation of the two groups of samples are as follows:1) Al-Cu matrix alloy and Z=(?)exp(226.1 x 103/RT).2) CNTs/Al-Cu composites and Z=(?)exp(327.7 x 103/RT).④ The optimum processing parameters for hot working is 300-350 ℃ /4.48-l2.18s-1;350-380℃/2.7-7.41-1 for Al-Cu matrix alloy and CNTs/Al-Cu composites at a true strain of 0.6, respectively.