Effect of high pressure on solidification microstructure evolution of near-eutectic Al-11.5Si-0.5Fe-0.2 Mg alloy

Abstract

The microstructures evolution of near-eutectic Al-11.5Si-0.5Fe-0.2 Mg alloy solidified under different pressures (1 GPa and 3 GPa) were investigated. The results show that the increase in solidification pressure leads to a transition from the typical eutectic structure to the hypoeutectic structure of the alloy by increasing the melting point, and a change in the morphology of the eutectic Si phase from a needle-like structure to a short sheet-like structure and contact with each other. The increase of solid solubility drives the disappearance of the π-Al8FeMg3Si6 phase at 1 GPa, the disappearance of the α-Al8Fe2Si phase, and the occurrence of the δ-Al4FeSi2 phase at 3 GPa. The α-Al8Fe2Si phase and β-Al5FeSi phases are separated from each other in the matrix, indicating that these two phases are formed by independent reactions. In contrast, the β-Al5FeSi and δ-Al4FeSi2 phases can remain stable during solidification at higher pressures.