Effect of Processing Conditions on Microstructure and Thermal Conductivity of Hot-Extruded Aluminum/Graphite Composites

Abstract

Aluminum/graphite composites have been successfully prepared by a hot-extrusion technique. The effects of processing conditions such as graphite particle size, graphite content, and extrusion temperature on extrusion behavior, microstructure, texture, and thermal conductivity have been systematically investigated. During the hot extrusion, the graphite was subjected to deformation and hence distributed along the extrusion direction in the extruded Al/graphite composites. The (00l) basal planes of the graphite were preferentially orientated along the extrusion direction. The preferred orientation of the graphite resulted in an anisotropy of thermal conductivity in the extruded samples. On the other hand, the utilization of bimodal graphite powder consisting of coarse and fine particles is beneficial to the enhancement of both relative density and thermal conductivity. Moreover, when a pressed green compact was rotated 90°and then subjected to the hot extrusion, the resulting composite exhibited higher thermal conductivity due to its higher density, fewer Al/graphite interfaces, and higher orientation degree of the graphite.

Microstructure and tensile properties of in-situ synthesized and hot-extruded aluminum-matrix composites reinforced with hybrid submicron-sized ceramic particles

“…As the extrusion proceeded, the pressure decreased slowly with increasing the stroke as seen in the region “C.” The decrease in extrusion pressure after the maximum pressure is due to the reduced contact surface area and thus reduced frictional resistance. Similar behavior has been also observed by Yi et al 30 during the extrusion of Al/graphite composites.

Figure 6.Extrusion pressure-stroke curves for 20 vol% AMCs extruded at different temperatures.

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“…The decrease in extrusion pressure after the maximum pressure is due to the reduced contact surface area and thus reduced frictional resistance. Similar behavior has been also observed by Yi et al 30 during the extrusion of Al/graphite composites.…”

Microstructure and thermal properties of nickel-coated carbon fibers/aluminum composites

“…These carbon reinforced Al-matrix composites are widely used in thermal management fields due to their high thermal conductivity (TC), low coefficients of thermal expansion (CTE), and light weight. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] However, two key issues in carbon/Al systems are of great concern. (i) At relatively low processing temperatures, the bonding compatibility between Al and carbon is very weak, thus resulting in the formation of pores and other defects at carbon/Al interfaces.…”