Nucleation and Growth of Fe-Rich Phases in Al-5Ti-1B Modified Al-Fe Alloys Using Synchrotron X-Ray Imaging and Electron Microscopy

The plate-like Fe-rich intermetallic phases directly influence the mechanical properties of recycled Al alloys, thus many attempts have been made to modify their morphology. Here, through synchrotron X-ray imaging and electron microscopy, we reveal the underlying nucleation and growth mechanism of Fe-rich phases during the solidification of Al-5Ti-1B inoculated Al-2Fe alloys. The experiment results shown that Al-5Ti-1B grain refiner and applied pressure both reduce the sizes and number of primary Al 3Fe phases, and promote the formation of eutectic Al6Fe phases. The tomography results shown that Al-5Ti-1B change the 3D morphology of primary Fe-rich phases from rod-like to branched plate-like and reduced their thickness and size. This is attributed to the Ti-containing solutes in the melts retard the diffusion of Fe atoms and the TiB2 provide possible nucleation sites for Al6Fe phases. The nucleation mechanism of Fe-rich phases is discussed in terms of experimental observation and E2EM model. It is suggested that the V segregated at the TiB2/Al6Fe interface and lower their mismatch and promote the transformation from Al3Fe to Al6Fe phases.