The solute atom distribution of the L1
2 ordered phase (Al
3X, X=Sc, Zr) was investigated for an Al–0.15 mol%Sc alloy and an Al–0.10 mol%Zr–0.05 mol%Si alloy using three-dimensional atom probe (3DAP) analysis and Monte Carlo simulation. Precipitates of the L1
2 ordered phase (Al
3X, X=Sc, Zr) in the Al–Sc and Al–Zr–Si alloy were detected using 3DAP analysis. The L1
2 ordered phase (Al
3X, X=Sc, Zr) in the Al–Sc and Al–Zr–Si alloy was evaluated quantitatively. Formation of the L1
2 ordered phase (Al
3X, X=Sc, Zr) was observed in the simulation with the interaction energy calculated using the first principle calculation. Si atoms were concentrated in the Al
3Zr phase and were positioned at Al sites in the Al
3Zr phase in the Al–Zr–Si alloy. The interaction energy between Si atom and Zr atom is negative: mutually attractive force exists between Si and Zr atoms. These results suggest that Si atoms are positioned at Al sites in the Al
3Zr phase and that they increase the frequency of the Al
3Zr phase nucleation.
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