A New Approach in Numerical Modeling of Inoculation of Primary Silicon in a Hypereutectic Al-Si Alloy

The applicability of classical heterogeneous nucleation theory for an inoculated Al-18.6Si (wt pct) alloy was investigated. Nucleation model proposed by Perepezko was used to study heterogenous nucleation of primary silicon in phosphorus-inoculated alloys. For this system, the nucleation temperature was found to be the most crucial variable in the model. If a spherical cap model is assumed for heterogenous nucleation, then the contact angle changes only by the interfacial energy. However, the data applied to Perepezko’s model showed it changed by undercooling. Therefore, it is suggested that the Perepezko’s nucleation model is not applicable for analyzing data in inoculated hypereutectic Al-Si alloy. Instead, for the first time, the free growth model developed by Greer to study the inoculation of Aluminum by Al-Ti-B was used for the Al-18.6Si (wt pct) alloy inoculated with Al-Fe-P. The results of modeling compared with the experimental data showed that the free growth model gives a closer approximation when predicting the size of the primary silicon in the investigated alloy. Mechanical properties of the as-cast hypereutectic alloys are influenced by size and shape of the primary silicon and eutectic silicon, type, size, and frequency of entrainment defects and residual stresses. Finer silicon particles lead to higher tensile strength in the cast components. Being able to predict the size of primary silicon particles will facilitate control of the inoculation process, to enhance mechanical properties such as tensile strength. Developed model here provides a basis to predict the size of primary silicon in hypereutectic Al-Si alloys treated with phosphorous-containing inoculants.