182 Prakt. Met. Sonderband 38 (2006) 
Deep etched images of AlSi12/Al,03/20s and AlSi18/Al,03/20s are depicted in Figure 6a,b Gmt 
and c,d, respectively. Like in AlSi7/Al,03/20s, interconnected Si plates are observable in schc 
the as cast condition for both studied composites (Fig. 6a,c). Si bridges connecting the Akac 
Al,Os-fibres are more often observed in AlSi12/Al,03/20s and AlSi7/Al,03/20s (in as cast) SUPE 
than in AlSi18/Al,03/20s material. Coarsened Si particles formed after 4h of solution Four 
treatment are observed sticking to the Al,Os-fibres (Fig. 6b,d). The isolated Si inclusions 
inside the matrix are washed away during deep etching. The reinforced hypereutectic 
matrix contains big primary Si particles (of about 10*um3) connecting various alumina RE! 
fibres. 
[1] 
Fig. 5: Si-Al,O3 structure [2] 
extracted by the [3] 
dissolution of a-Al in 
AISi12/A1,03/20s (a,b) & [4] 
AISi18/A1,03/20s (c,d): 
a,c) as cast and b,d) [5] 
after solution treatment, [6] 
respectively. 
si bridge ticles 
Au 10pm 
4. CONCLUSIONS 
The 3D-representation of the studied unmodified AlSi-alloys presents a lamellar Si 
morphology with interconnecting nodes. In case of AlSi7 alloy, regions with parallel Si 
plates of different orientations were observed. The addition of 170ppm Sr produced full 
modification of the eutectic Si-structure into a fibrous morphology. The observed Si fibres 
are mostly interconnected and their orientation depends on the grain orientation. The 
thickness of Si fibres and branches increases towards the Si-free grain boundaries. 
All studied composite materials present an interconnected Si-Al,O3 structure which 
remains stable even in the T4 condition. Si plates bridging the Al,Os-fibres are observed in 
the as cast condition, while coarsened Si particles are mostly observed after 4h of solution 
treatment. The reinforced hypereutectic matrix contains primary Si particles connecting 
various alumina fibres independent from solution treatment. 
ACKNOWLEDGEMENTS 
F. Lasagni would like to thank the ADEMAT Network (EU-Alfa || Programme) and the 
Austrian Non Kplus-programme (via ARC Leichmetallkompetenzzentrum Ranshofen