Growth characteristics of eutectic silicon in unmodified and Srmodified Al-12.7%Si alloys investigated by SEM/EBSD
Xiaorui Liu,a,b,c Yudong Zhang,b,c, Benoît Beausir,b,c Fang Liu,d Claude Esling,b,c
Fuxiao Yu,d Xiang Zhaoa and Liang Zuoa,*
a
Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education),
Northeastern University, Shenyang 110819, China
b
Laboratoire d'Étude des Microstructures et de Mécanique des Matériaux (LEM3), CNRS
UMR 7239, Université de Lorraine, 57045 Metz, France
c
Laboratory of Excellence on Design of Alloy Metals for low-mAss Structures (DAMAS),
Université de Lorraine, 57045 Metz, France
d
School of Materials and Metallurgy, Northeastern University, Shenyang 110819, China
Abstract
Based on scanning electron microscopy (SEM) and electron backscatter diffraction
(EBSD), the growth characteristics of eutectic silicon in unmodified and Sr-modified Al12.7%Si alloys were investigated by microstructure-correlated crystallographic analyses at a
large scale. For the unmodified eutectic Si, the formation of repeated single-orientation twin
variants enables rapid anisotropic growth in the twin plane re-entrant edge (TPRE) manner. A
preferred Si extension occurs at <1 1 0> direction, other than the typical <1 1 2> direction
assumed by the TPRE mechanism. With addition of the Sr modifier, substantial change
appears in the eutectic Si morphology, attributable to the restricted TPRE growth and impurity
induced twinning (IIT) growth. The former enhances lateral growth by forming new twins
with parallel twinning planes, while the latter leads an isotropic growth by forming differently
oriented twins. In both alloys, local stresses caused by a large difference in thermal expansion
between Si and α-Al - are released by the deformation of soft α-Al, thereby producing
abundant low-angle misorientations. No representative orientation relationship (OR) exists
between eutectic Si and α-Al due to their incompatible growth and incompatible thermal
expansion. The present result is expected to provide new insights into the solidification
behaviors of eutectic phases.