The mechanism of Fe-rich intermetallic compound formation and growth on inoculants revealed by electron backscattered diffraction and X-ray imaging

Fe-rich intermetallics affect critically the mechanical properties and recyclability of aluminium alloys. Increasing effort has been spent on the inoculation of these intermetallics, hoping to promote a finer dis-tribution. Recently Al-5Ti-1B (wt.%), originally developed to refine a-Al, has been shown to refine Al13Fe4, an intermetallic phase present in a variety of Al alloys. However, mechanisms of the formation and growth of the intermetallics on the inoculants are unclear. In this paper, Ti is added to Fe-containing Al alloys to produce a large number of potent Al3Ti particles, the active inoculant in Al-5Ti-1B. We use a combination of electron backscattered diffraction, in situ synchrotron X-ray radiography and post- solidification X-ray computed tomography to investigate the formation and growth of primary Al13Fe4 on Al3Ti inoculants, first in a model Al-Fe alloy, with key insights then confirmed in a high Fe- containing, recycled 6xxx alloy. Crystallographic orientation relationships between Al13Fe4 and Al3Ti are analysed comprehensively, and the formation and growth dynamics of Al13Fe4 on Al3Ti is also unveiled. A strong link is revealed between the formation of Al13Fe4 on Al3Ti and a twinning-related pseudo-symmetry of Al13Fe4. Finally, a potential strategy to refine both intermetallics and a-Al in recy- cled alloys with elevated Fe concentration is proposed.& COPY; 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Fe-rich intermetallics have a significant impact on the mechanical properties and recyclability of aluminium alloys. This paper investigates the formation and growth mechanisms of primary Al13Fe4 on Al3Ti inoculants through various analytical techniques. The study reveals the crystallographic orientation relationships between Al13Fe4 and Al3Ti, as well as the correlation between the formation and growth dynamics of Al13Fe4 and a twinning-related pseudo-symmetry of Al13Fe4. A potential strategy to refine both intermetallics and a-Al in recycled alloys with elevated Fe concentration is proposed.