The present work shows how it is possible to use computational modelling for the prediction of phase transformation processes in cast aluminum-ironsilicon alloys. Correlation between experimental and modelling data is also discussed. Modelling of alloys phases doesn`t give the actual structure components information, however it allows for prediction of phase transformations during structure formation process under cooling.
Alloy
Distribution curves of phases in terms of variation in the concentration of silicon were obtained by composition modeling
(fig. 1, 2). The regions of solid-solutions existence, secondary phases crystallization and liquid-solid equilibrium curves
can be defined on the resulting phase diagrams. The modelled results correspond to the theory [
Obviously, more silicon addition into the alloy results in differences in starting and finishing of crystallization, scale of temperature crystallization intervals and positions of the “liquid + solid = solid” transformations. Of course, the presence of these high temperature calculated phases in actual alloys was not proved by metallography; however, during crystallization at low cooling rates the liquid phase might have zones with abnormal chemical composition which was formed by a decrease in the content of alloying elements in the liquid phase situated among solid solution crystals. While crystals of solid solution or chemical phase grow, the content of alloying elements in the liquid phase decreases significantly. This leads to the formation of these zones with an unequal distribution of alloying elements in liquid phase. c) Figure 1 – Calculated phase diagrams for alloys: a) 92%Al-6%Si-2%Fe; b) 94%Al-4%Si-2%Fe;c) 96%Al-2%Si-2%Fe c) Figure 2 – Calculated phase diagrams for a) 93,5%Al-6%Si-0,5%Fe; b) 95,5%Al-4%Si-0,5%Fea) 97,5%Al-2%Si0,5%Fe
It is suggested that iron containing phases at high temperature are saturated by silicon. This results in diffusion of silicon from iron containing phases during further cooling down to 250 °C. Thus, modeling allows getting reasonable representations of the phase composition information in the high temperature region and expected temperatures of phase transformation areas as well as values of changing of elements percentage in phases during crystallization at low cooling rates. On the basis of simulated diagrams, it becomes possible to choose alloy compositions and technologies for experimental alloys manufacturing which will be the next step of current work in searching of advanced thermally conductive cast aluminum alloys compositions.