178 Prakt. Met. Sonderband 38 (2006) 
The understanding of the three-dimensional architecture of eutectic alloys and short fibre 3. } 
reinforced composite materials is the basis for further improvement of the mechanical 
properties of these materials [4]. In this work, a three-dimensional study of the Al-Si The 
eutectic is performed. Different AISi unreinforced alloys and short fibre composite AIS 
materials are investigated by means of a new focused ion beam (FIB) 3D sectioning and 
method and deep etching. lam 
pha 
prin 
2. EXPERIMENTAL beh 
of 
Two unmodified AlSi7 and AlSi12 alloys and one eut 
Sr-modified AISi7 alloy were squeeze cast by LL der 
LKR Ranshofen, Austria. A 20 vol.% alumina Alloy Si Fe Cu-Ni Sr 
preform was infiltrated with AISi7, AlSi12 and AlISi7 7.04 0.07 <0.01 
AlSi18 matrices in order to produce short fibre AISi7Sr 6.95 0.07 <0.01 0.017 
reinforced samples (SFRM). The composition of AlSi12 11.87 0.08 <0.01 - 
the alloys is depicted in Table 1. Samples of AlSi18 17.86 0.16 <0.01 - 
5Sx5äxamm® were cut and solution treated in a in Table 1. Composition of the AlSi based _ 
a Linn High Therm furnace model 70.26 at alloys [wt.%] (Al: balance). 
540°C during 4h (T4) followed by water 
quenching 
2.1 METALLOGRAPHIC CHARACTERIZATION 
For conventional metallographic characterization, the materials were ground with 320, 500, 
1000, 2400, 4200 Struers SiC paper (using water as coolant with a rotating speed of 
300rpm) and subsequently polished with DP-diamond paste of 3 and 1um particle 
diameter (with a rotating speed of 150rpm and Dp-Lubricant blue (Struers) as coolant). 
Final polishing was performed with an MgO suspension. 
2.2 DEEP ETCHING 
As cast and solution treated samples of approximately 5x5x5mm® were submerged into a 
17wt.% solution of HCI during ~48h. In this way, the aluminium phase of the materials is 
dissolved extracting the structure of Si and/or alumina, inert to the attack of the acid. The 
extracted structure was analysed by means of a scanning electron microscope with field 
emission gun (FEG SEM). 
2.3 3D FIB/FIB-EDX METHOD 
The 3D reconstruction of Al-Si alloys was performed using a 3D FIB sectioning method 
similar as described in [5]. The FIB microscope consisted of a Dual Beam Workstation 
(FEI Strata DB 235) using the electron beam for imaging and the focused ion beam (Ga) 
for milling of the sample and Pt deposition. Usually, FIB sectioning employs a combination 
of sample milling and secondary electron imaging. The resolution of the reconstructed 
material depends on the precision of individual FIB cuts and secondary or backscatter 
electron (SE/BSE) images. However, some materials do not provide sufficient SE/BSE 
contrast between their phases. In this case, the element specific X-ray emission (EDX) Th 
signal may be used in addition to the SE images. Using this approach, the resolution 
depends on the precision of FIB milling and on that of the EDX mapping. The latter pre 
depends on the material and acceleration voltage of the electron beam. Further details are SC 
given in [6]. Mi 
ar