Thixoforming : Semi-solid Metal Processing

224j 7 A Physical and Micromechanical Model for Semi-solid Behaviour
Figure 7.1 Photomicrograph of the microstructure of an
Sn–15wt%Pb alloy after water quenching from the semi-solid
state with 0.6 solid fraction. The microstructure reveals a light
primary solid phase and a dark eutectic phase corresponding to
the solid phase and to the liquid phase present in the semi-solid
state, respectively.
importance to the active zone where the strain is mainly localized, the material is
represented by a morphological pattern as follows: thanks to the random and
consequently spherical symmetry (isotropic) distribution of the constituents (whatever
the real form of the solid and liquid particles ), the coated inclusion is
considered as spherical (Figure 7.2, B). The inclusion is composed of both solid
and liquid with volume fractions f s l
I and f I , respectively, to represent entrapped liquid
within solid particles. It is surrounded by a coating (the active zone) composed of the
solid bonds and the non-entrapped liquid with volume fractions f s l
A and f A , respectively.
From this statistical point of view, when the real material is subjected to either
Figure 7.2 (A) Schematic representation of the semi-solid
microstructure exhibiting the presence of one inclusion of solid
and entrapped liquid surrounded by a coating of liquid and solid
bonds. (B) Morphological pattern constituted of a coated
inclusion embedded into a matrix having the effective properties
of the heterogeneous semi-solid material.