3. Results and Discussion
Modelling of different compositions of alloys aluminum-silicon with further obtaining the
distribution curves of phases in axes of variation of the silicon concentration were obtained
previously [
4
]. Some parts of phase diagrams including the regions of solid solutions, secondary
phases and liquid-solid equilibrium curves were defined [
4
]. The obtained structures (fig. 1) for
the alloys with the compositions Al-0%Si-1%Fe; Al-2%Si-1%Fe and Al-4%Si-1%Fe showed that
there were significant changes with increasing the silicon in presence of silicon crystals on the
grain boundaries of solid solution The modelled results [
4
] correspond to the theory [
2-3
]. In
modelled results it was discussed the behavior of iron as an element affecting the stability of
ironcontaining phases in “liquid + solid = solid” transformations [
4
]. Obviously, iron is could be a
part of solid solution, which was dissolved in a matrix of solid solution during crystallization. The
obtained temperature boundaries in paper [
4
] of each phase showed how the concentration of
silicon changed: it was reducing during cooling in all phases. In present results the character of
the alloys at room temperature showed that the increasing the amount of silicon mostly results in
free silicon phase distribution on the boundaries of grains. Reducing of silicon concentration in
every phase influences on final structure components distribution. The major goal of the work is
to find how the final properties of experimental alloys correlate with predicted properties as well
as what is the use of modern modelling in understanding of real structure formation process.
Fig. 1. Images of: a) Al-0%Si-1%Fe; b) Al-2%Si-1%Fe; c) Al-4%Si-1%Fe
It was discussed [
4
] more silicon addition into the alloy input resulted in start and finish of
crystallization, position of temperature crystallization intervals and positions of the
transformations. During crystallization, big impact has cooling rate, because at low cooling rates
the liquid might have zones with not equivalent chemical compositions, which finally lead to
form phases with different composition of alloying elements like silicon and iron. While crystals
of solid solution or chemical phase grow, the content of alloying elements in the liquid phase
decreases significantly. Crystals of pure silicon of silicon phase easily distribute on the boundaries
of grains of the solid solution. At high cooling rates, the content of silicon will be higher in solid
solution and other silicon containing phases. Thus, fixation of high temperature state leads to
reduce amount of free silicon, however, if material is heated, diffusion processes and
recrystallization will reverse silicon to grain boundaries. It was also suggested that iron-containing
phases at high temperature are saturated by silicon.
Thus, modeling gives adequate understanding of a phase composition existence in different
temperature regions and expected temperatures of phase transformation areas. However,
experimentally obtained alloys might have the unequal content of phases compared to modelled
results. Based on simulated diagrams, it is possible to choose an alloy composition, but it is
difficult to predict phase distribution in a final structure. Because final structures will be different
for the alloys cooled with different cooling rates.