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The atomistic behaviors of microalloying elements during phase decomposition of Al- Cu-Mg, Al-Zn-Mg and Al-Mg-Si alloys have been systematically predicted in terms of two-body interaction energies between solutes and/or vacancies. The utilized first-principles calculation based on generalized gradient approximation (GGA) and full-potential Korringa-Kohn-Rostoker (FPKKR) Green’s function method accurately estimated such fundamental energies in good agreement with experimentally reported behaviors: e.g. vacancy-trapping model, vacancy-sink model and nanocluster assist processing. The proposed interaction energy maps (IE maps), in which the estimated interaction energies are plotted along the rows of the periodic table, are quite useful for designing new aluminum alloys with microalloying elements.

We present systematic ab-initio calculations for nonmagnetic (NM), ferromagnetic (FM), and antiferromagnetic (AFM) states of fullHeusler alloys (X 2 YZ) such as Co 2 MnSi (X = Co, Y = Mn, Z = Si), Ni 2 MnAl (X = Ni, Y = Mn, Z = Al), and Ru 2 MnSi (X = Ru, Y = Mn, Z = Si). The calculations are based on the all-electron full-potential (FP) screened Korringa-Kohn-Rostoker (KKR) Green's-function method combined with the generalized-gradient approximation in the density-functional formalism. We show that the present calculations reproduce very well the experimental ground states of these alloys (FM of Co 2 MnSi and Ni 2 MnAl, AFM of Ru 2 MnSi) and the available measured values for lattice parameters and magnetic moments. It is also shown that the fundamental features of the magnetism of Co 2 MnSi (strong FM) and Ni 2 MnAl (weak FM) are understood by using the Mn spin-flip energies and the Mn-Mn exchange interaction energies in X (= Co, Ni), both of which are obtained by the present FP-KKR calculations for the impurity systems. We can show that the magnetism of Ni 2 MnAl may be changed from FM to AFM by atomic disorder (B2-structure) occurring at elevated temperatures.

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