Composite Materials Research Progress

292
S.C. Tjong
(a)
(b)
Figure 19. TEM micrograhs of (a) unreinforced pure Al after eight passes and (b) Al/5 vol.% Gr
composite after four passes at room temperature [29].
ECAP treatment of Al-based composites at room temperature is particularly attractive
from the economic viewpoint. Proper selection of reinforcing particulates that experience no
cracking is of technological interest. Very recently, Saravanan et al. used ECAP to refine the
matrix grains of the Al/5 vol.% Gr (65 μm) composite at room temperature [29]. The soft and
self lubricating nature of graphite can prevent the fracture of particulates during ECAP
treatment. Figs. 19(a) shows a typical TEM micrograph of pure aluminum after eight ECAP
passes at room temperature. The microstructure is characterized by well defined subgrains
with a size of ~ 620 nm. In contrast, a significant grain refinement, down to the
submicrometer level of ~ 300 nm can be achieved by pressing the Al/5 vol.% Gr composite at