Prakt. Met. Sonderband 46 (2014) 383 
along the <112>s; growth direction of Si promotes the formation of further parallel Si twins 
with a higher number density. According to the IIT mechanisms, the adsorption of Sr at the 
affect on Si intersection of two {111}s; twins promotes the formation of multiply Si twins. 
a (up to 160 
is along the u 
vinning was ha 
anism. This . “ 
0 significant . ) 
and at the — £ 
eutectic Si = 
ccur during = . 
ne Si phase 5, =z 
pos 
a La 
Fig. 4: Schematic representation of the adsorption of Sr atoms along the <112>g; growth 
direction of Si and at the intersection of Si twins, forming Si twinning, and the solute 
entrainment of Sr atoms, forming Al,Si,Sr particle within eutectic Si. (a) Equilibrium 
solidification, (b) The adsorption of Sr atoms occurs along the <112>g; growth direction of 
Si and at the intersection of Si twins, forming Si twinning, (c) Sr adsorption occurs along 
other <112>g; growth direction of Si and at other intersection of Si twins, forming parallel or 
multiply Si twinning, (d) Sr solute entrainment occurs, forming Sr-rich clusters. finally 
Al,Si;Sr particle within eutectic Si. 
The adsorption of Sr atoms at the intersection of Si twins and / or along the <112>g; growth 
-5Si-6100 direction can also occur during further eutectic Si growth, which may also yield further re- 
cluster and entrant edges of Si twinning or a change of stacking sequence of Si twinning (Fig. 4c). In 
this case, eutectic Si growth will re-start from another {111}s; plane. Similarly, an 
enrichment of Sr and Al atoms in a local area and another multiple Si twinning occurs. 
Finally, once the {111}s; planes fold on each other, the solute impingement and 
subsequent entrainment of the segregation fields occurs (Fig. 4d). On subsequent cooling, 
the solute entrainment forms AI-Si-Sr-rich particles with different morphologies and 
segregation compositions, which are mostly likely to be Al,Si;Sr phase if the cooling rate is low 
ic Si in Al-Si enough, or the segregation time and length is sufficient enough. 
/ distributed, The proposed solute entrainment can be used readily to interpret the observation of the Al- 
growth (Fig. Si-Sr-rich clusters in present investigation and previous reports using APT [8]. The 
1 and kg, < observed AI-Si-Sr-rich clusters can be an “artefact” caused by solute entrainment, rather 
head of the than an active factor affecting the modification. However, the observed Al-Si-Sr-rich 
Sr atoms on clusters exhibits the position of the solute adsorption and subsequent entrainment during 
tersection of eutectic Si growth, i.e. along the <112>s; growth direction of Si and / or at the intersection 
yrotion of Sr of two {111}s; twins. Therefore, it is proposed that the adsorption of Sr is a dominant factor