The interaction between Eu and P in high purity Al-7Si alloys

The interaction between Eu and P in high purity Al-7Si alloys was investigated. Interrupted solidification experiments were undertaken to study macrostructure evaluation and thermal analyses were performed to obtain characteristic temperatures of the eutectic reaction. Without the presence of Eu, increasing P concentrations results in a significant increase in the number of eutectic grains due to the formation of AlP particles, which can act as nucleation sites for eutectic Si. With the presence of Eu, a decrease in nucleation frequency and thereby an increase in eutectic grain size was observed in alloys containing 5 and 30 ppm P due to the interaction between Eu and P, which can be further supported by the results of μ-XRD patterns and SADP of TEM. It was found that most P-rich particles were covered by Eu-rich intermetallics, which are indexed to be Al2Si2Eu phase, indicating that the formation of the pre-eutectic Al2Si2Eu phase may lead to a depletion of pre-existing AlP particles or residual P in the melt. This investigation highlights the effect of the interaction between Eu and P on the nucleation of eutectic Si and eutectic grains.