Composite Materials Research Progress

280
S.C. Tjong
applications. Goujon et al. prepared the Al 5000/AlN (4-30 vol.%) nanocomposites though
cryomilling of 5000 Al powder (380 nm) and AlN particle (150 nm) followed by hot pressing
[12, 13]. Cryomilling for 6 h is required to obtain a good homogeneity of powder mixtures.
The crystallite sizes of Al and AlN in the powders are reduced to about 49 and 30 nm,
respectively. Hot pressing leads to homogeneous dispersion of the AlN phase in the Al alloy
matrix and to an increase of the crystallite size of Al to submicrometer regime but not of AlN
(Fig. 6). The microstructure of this composite consists of UFG aluminum grains free of AlN
particles and regions dispersed with AlN nanoparticles.
Figure 4. SEM micrograph showing the microstructure of as-cast A356/2%SiC nanocomposite [10].
Figure 5. TEM micrograph showing agglomeration of particulates at the grain boundary of Al/5 vol.%
Al2O 3 nanocomposite. The mean size of alumina nanoparticles is ~ 50 nm [36].