Prakt. Met. Sonderband 38 (2006) 179 
ort fibre 3. RESULTS & DISCUSSION 
chanical 
he Al-Si The microstructures of as-cast AISi7, AISi12 and AISi7Sr alloys and AlSi7/Al;03/20s, 
mposite AlSi12/Al,04/20s and AlSi18/Al,03/20s composite materials are depicted in Figures 1a-c 
ectioning and d-e, respectively. The a-phase of AlSi7 is enclosed by the eutectic structure of 
lamellar Si. The measured amount of alpha is about 73vol.% although the equilibrium 
phase diagram predicts 50vol.%. AlSi12 presents a mostly eutectic microstructure with few 
primary Si (<0.1vol.%). The a-phase occupies almost 27vol.% which means that the alloy 
behaves hypoeutecticly due to the fast solidification rate of squeeze casting. The addition 
of about 170ppm Sr produced full modification of the eutectic structure from a lamellae 
eutectic morphology into a coral-like structure. The AISi7Sr presents about 76vol.% o- 
Sh dendrites enclosed by the Al-Si eutectic. 
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kscatter Fig. 1: Microstructure of a) AlSi7, b) AlSi12, c) AISi7Sr and d) AISi7/Al;03/20s, 
SE/BSE e) AISi12/A1,04/20s, f) AISi18/Al,03/20s in the as cast condition 
Due) The microstructure of the composites’ matrices is similar to that of the unreinforced alloys, 
we latter presenting o-dendrites enclosed by the eutectic structure in AlSi7/Al,03/20s. The 
tails are secondary dendrite arm spacing of about 20um is in average significantly smaller than that 
of the unreinforced casting. The eutectic is concentrated around fibres indicating that 
solidification started in between. About 15vol.% a-phase can be observed between the 
eutectic for the AISi12/Al,01/20s composite. The AISi18/Al,03/20s composite shows