Growth Mechanisms of Faceted Al 3Fe Intermetallic Revealed by High-Speed Synchrotron X-Ray Quantification

Abstract

High-speed synchrotron tomography was used to investigate the nucleation and growth dynamics of Al3Fe intermetallic during solidification of an Al-5wt%Fe alloy, providing new insights into its formation mechanisms. The majority of Al3Fe intermetallics nucleated at the surface oxide of the specimen and a few nucleated at Al3Fe phase. Al3Fe crystals grew into a variety of shapes, including platelet, stepped and bended, which can be attributed to the crystal structure of this compound and its susceptibility to twinning. Hole-like defects filled with aluminium melt were observed within the intermetallics. Large Al3Fe crystals imaged after deep etching were shown to be made of small crystal subunits. Based on this observation, tiling of precusor subunits was proposed to explain the formation of the Al3Fe intermetialic. These insights are not only vital for the development of crystal growth models but aslo valuable to aluminium alloys recycling industries.