180 Prakt. Met. Sonderband 38 (2006)
mostly an eutectic microstructure with ~3vol% of primary Si inclusions. Although the AISi18 Fig
matrix is an hypereutectic alloy, about ~2vol.% of a-Al is observed. Sal
The architecture of the reconstructed eutectic Si in AISi7 is depicted in Figure 2a, where fibre
lamellar Si plates of about 1~3um thickness are observed. The different interconnected In N
structures are presented in individual grey tones. Two different regions with different nan:
preferential Si orientation are observed. Both regions seem to be connected by several 4b
nodes of about 1-4um? (see Figure 2b). This observation corroborates the formation of a intel
Si-network studied in a previous work [1]. The real size of the Si plates is not observed iii
since the 3D reconstructed volume was only about 25um in the milling direction (y-axis). Der
Deep etching imaging of chemically extracted Si revealed plates between 40-80um long Incr
and wide [1]. Therefore, the observed small isolated particles are probably connected to
the main structure outside the investigated volume. ‘a
Sum |
Fig. 2: Reconstructed images of the 3D morphology of AISi7 in the as cast condition: Fie
a) Si structure with interconnecting Si plates and b) connecting nodes in detail. ’
The 3D-morphology of the eutectic Si phase in the unmodified AlISi12-alloy (Figure 3a) is .
similar to that of AISi7, but thinner Si plates of about 0.5-1um in width are observed. The
studied region presents Si lamellae with similar relative orientation compared to that of
AISi7, where almost perpendicular plates are found. Like in AlSi7, these Si plates are
connected in several nodes (some of them indicated in Figure 3b).
Figt
fron
con
with
trea
| J AIS
Fig. 3: 3D Reconstruction of the Si structure in AlSi12 in the as cast condition zon
a) branched Si lamellae and b) detail of connecting nodes ren