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