On the characterization of primary iron-rich phase in a high-pressure die-cast hypoeutectic Al-Si alloy

Abstract

The morphological properties and distribution characteristics of primary iron-rich phase in a high-pressure die-cast hypoeutectic Al-Si alloy were investigated by synchrotron X-ray tomography technology. Attention was focused on the formation and evolution mechanism of primary iron-rich intermetallic compounds (IMCs) in high pressure die casting (HPDC). Results show that two different sizes of primary iron-rich phases included externally solidified primary iron-rich phase I ((P-IMC)I) and primary iron-rich phase II ((P-IMC)II). The morphology of (P-IMC)I was close to a hexahedron while (P-IMC)II was nearly a spherical particle. Both (P-IMC)I and (P-IMC)II enriched in the central area and their volume fraction maintained a high level from defect band to center. Phase calculation show that (P-IMC)I (601 °C) preferentially precipitated from liquid and its further growth led to the decrease of Mn/Fe ratio in the subsequent formed (P-IMC)II. In HPDC solidification process, (P-IMC)II exhibited a lateral growth pattern with the terminating surfaces determined to be {1 1 0} planes. In addition, the hexahedral (P-IMC)I in central ESCs-rich zone developed into a dendrite along its corner<100>direction.