Anomalous Behaviour of Nb in the Formation of Fe-Rich Intermetallics in Al–Si–Fe-Type Alloy.

In this work, the effect of Nb addition on the evolution of Fe-rich intermetallics in Al–Si–Fe-type alloy has been investigated through melting and casting method. Electron microscopy (SEM) has revealed that Nb behaves distinctly in the Al–Si–Fe alloy, when it is added in the form of Al–10Nb master alloy compared to the same added in the form of elemental powder. Results indicate that some Nb atoms, together with Al–Si–Fe, form a quaternary, Al₈(FeNb)Si-type intermetallic phase, in the elemental Nb powder inoculated Al–Si–Fe alloy. In contrast, no such phases were observed when Nb was added to Al–Si–Fe melt in the form of Al–10Nb master alloy. The possible phase evolutions mechanisms have been discussed herein. Figures 1c and 2a, respectively, represent the SEM–EDS elemental mapping of Al₃Nb particles found in the as-cast Al–Si–Fe alloy inoculated with Al–10Nb master alloy, while Figs. 1d and 2b show the SEM–EDS elemental mapping of Al₃(FeNb)Si particles found in the as-cast Al–Si–Fe alloy inoculated with elemental Nb powder. Results show that Al₃(FeNb)Si particles are absent in the as-cast Al–Si–Fe alloy inoculated with Al–10Nb master alloy. [ABSTRACT FROM AUTHOR]