Prakt. Met. Sonderband 38 (2006) 177 
eiten als THREE DIMENSIONAL STUDY OF Si-EUTECTIC STRUCTURES 
‚äufigere IN UNREINFORCED AND SHORT FIBRE REINFORCED Al- 
ALLOYS 
iedlicher 
antitative F. Lasagni*, A. Lasagni**, C. Holzapfel**, F. Mucklich**, H.P. Degischer* 
Institute of Materials Science and Technology, Vienna University of Technology, 
Karlsplatz 13/E308, A-1040 Vienna, Austria. 
Functional Materials — Department Materials Science, Universitat des Saarlandes, 
els FIB- Gebäude 22, 7. Etage, P.O.Box. 15 11 50 - D-66041, Saarbrücken, Germany. 
der 3D- 
arakteris- 
fnahmen 
(Nv) und ABSTRACT 
iedlicher, 
utung far In this work, a detailed study of different eutectic architectures in unreinforced and 
ion des reinforced AlSi(Sr) alloys is performed. In a previous work [1], the 3D morphology of deep 
etched Al-Si alloys was investigated, where an interconnected Si-network was observed in 
the as-cast condition for both unmodified and modified alloys. During solution treatment, Si 
spheroidizes changing its morphology from a lamellar (in case of the unmodified alloys) or 
edanken a coral-fibrous structure (for the Sr modified-AlSi) into round Si particles, where the 
as ITWM connectivity between the Si is disintegrated. The addition of Al,Os-short fibres has avoided 
s, die im the disintegration of the Si-network even after longer exposure times at 540°C. This was 
erkstoffe observed in deep-etched samples for which a 3D-Si/Al,O3 network was obtained after 
chemical dissolution of primary-Al. 
A new Focused lon Beam-Energy Dispersive Spectroscopy (FIB-EDX) method was 
implemented to study the 3D architecture of as cast and solution heat-treated Al-Si-alloys. 
These 3D structures can be reconstructed from sequential 2D sectioning and subsequent 
computer imaging. The obtained spatial resolution is higher than that achieved by 
.G., Lee, synchrotron radiation computer tomography 
;0C. 216, 
Science”, 1. INTRODUCTION 
Aluminium-alloys with Si as the major alloying addition (>4at.%) are the most important of 
3-410 the Al-casting alloys mainly because of the high fluidity imparted by the presence of 
ubmitted relatively large volumes of the Al-Si eutectic. Binary hypoeutectic Al-Si alloys contain 
lamellar eutectic silicon dispersed in-between the primary Al dendrites forming a 
3d 2006) percolating Si network [1]. They exhibit low ductility in the as cast condition, because of the 
brittle nature of the silicon plates usually bigger than 10um. These alloys can be modified 
33, 1991, and/or heat-treated to improve their ductility. The addition of little Sr (0.01-0.03wt.%) is 
sufficient to bring out full modification with a completely fibrous morphology of the network 
improving both ductility and tensile strength in the alloys [2-3]. 
The main reason for a solution treatment in alloys of the Al-Si system is not to dissolve the 
s/Plenum Si phase, the solubility of which is only 1.6 wt.% at the eutectic temperature (1.2 wt.% at 
540°C). Actually, the main objective of the solution treatment of alloys containing more 
03, 454- than 2 wt.% Si is the spheroidization of the eutecticly segregated Si. improving the ductility 
of the eutectic material.