Microstructural Characterization of Gas Atomized Al-10Si-4Fe Alloy Powder

摘要

Rapid solidification processes (RSP) like gas atomization, might be used to increase the extension of the solid solubility limits of iron and silicon in the Al matrix and therefore to increase the formation of metastable crystalline phases or even to change the morphology and chemistry intermetallic phases. In this work, the microstructure of rapidly solidified Al-10wt%Si-4wt%Fe alloy powder was evaluated by using a combination of X-ray diffractometry-XRD, scanning electron microscopy-SEM and energy dispersive X-ray spectroscopy-EDS. The alloy was atomized with argon at pressure of 1,2 MPa and the superheating temperature of the melt was about 1100 K. The gas to metal mass flow ratio was 2,05. From the equilibrium diagram and associated phase fields in the Al-rich corner of the ternary AlFeSi phase diagram, it was expected the formation of α-AlFeSi intermetallic phase as the primary equilibrium phase. In addition, the α-AlFeSi grows with a non-faceted interface and its formation should be kinetically more favored than faceted-growing phases. However, XRD and SEM/EDS analysis identified monoclinic β-Al_5FeSi intermetallic and, tetragonal Al_9FeSi_3 as the phases observed in the microstructure. The later one is not expected in equilibrium diagram at all. Both phases grow with a faceted interface. It can be concluded that the high thermal undercooling promoted by gas atomization displaced the fields of phases stability and caused the observed microstructural variation.