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In Al–Cu–Li–Mg alloys, Li not only imposes the effects on the precipitation of T1, δ′, θ′, S et al., but also segregates to the S (Al2CuMg)/Al interface to stabilize the S precipitates. However, such segregation behavior could not be characterized experimentally at the atomic degree due to the low mass of Li. Also, the fine structure of S/Al interface is not yet clear. This work applied first-principles calculations to study these issues. The numerical values of surface energies for three non-stoichiometric surfaces (Al-1, Al-2, and CuMg terminations) of Al2CuMg (001) surface were calculated as ~ 1.3 J/m2 using a special method. The lowest energy of Al2CuMg (001)/Al (021) structure was obtained based on the calculation of energies and interface separated work. The segregation of Li at Al2CuMg (001)/Al (021) interface was clarified: (i) Li substituted not only one Al atom, but also all the Al atoms of the '3' layer rather than the '1'or '2' layer of the Al matrix side at the interface, (ii) Li that substituted Al atoms of the Al matrix side preferred to play on the role of Mg in Al2CuMg, trying to expand Al2CuMg bulk to maintain the interface stability, (iii) Li segregation is helpful to improve interface strength. This work provides a considerable insight for Li segregation to Al2CuMg (001)/Al (021) interface in Al–Cu–Li–Mg alloys. [ABSTRACT FROM AUTHOR]

To evaluate the alloying effect on Al–Li alloy, we conduct a theoretical exploration to predict the behaviors of Sc and Cu segregation to Al/δ′ interface. The results show that Sc tends to segregation at Al3Li layer by substituting Li atom, while Cu prefers to replace Al atom of Al layer at the interface. The improvement of interface strength caused by segregated Sc and Cu is similar. The analysis of electronic properties of solute Sc and Cu atoms suggests that the difference of atomic radius and the electronegativity between them contribute to the discrepancy of segregation paths. [ABSTRACT FROM AUTHOR]

The solidification behavior and intermetallic phase evolution during homogenization annealing of an Al–Zn–Mg–Cu alloy with 0.12 wt% Ce addition were examined. The residual Al2CuMg phase is completely dissolved after homogenization and is replaced by a large number of dispersed micro/nanoscaled AlCuCe enrichment phases within Al matrix. This change occurs because of the formation of a large number of finer lamellar eutectic network structures which are more easily dissolved into Al matrix during the homogenization process. In addition, the trapping of Cu atoms in the stable AlCuCe phase also prevents the formation of Al2CuMg phase, leading to the complete dissolution of Al2CuMg phase in the Al–Zn–Mg–Cu alloy. The grain refinement behavior in Al alloy with Ce addition is similar to that in alloys with the addition of Sc, because of the formation of primary Ce-enriched Al11Ce3 phase as the nucleation agent of α(Al) during solidification. [ABSTRACT FROM AUTHOR]

Segregation behaviors of Cu at α-Al (1 1 1) (1 1 1)/ δ′-Al3Li (1 1 1) interface were investigated with the first-principle pseudopotential plane-wave method. The results show that the most stable atomic coordination relations for α-Al (1 1 1)/δ′-Al3Li (1 1 1) interface is the structure of which the ABC stacking order of FCC lattice along (1 1 1) direction is kept at both two interfaces of Al and Al3Li phases. At 1/4 ML coverage, Cu atom is inclined to be segregated at α-Al (1 1 1)/δ′-Al3Li (1 1 1) interface by adopting the interstitial rather than the substitution mode. The favorite interstitial site is the position where Cu atom is surrounded by three symmetrical Al atoms. Based on the calculation of separation work, we predicted that interstitial Cu can effectively improve the strength of the whole interface region, especially the area inside Al matrix, this is in agreement with the experimental results. [ABSTRACT FROM AUTHOR]