Designing elastic modulus of Al3X precipitates in Al alloys by identifying effective atomic bonds and stabilizing coherent structures

Abstract

In Al alloys, many experiments have shown the effectiveness of Al3X precipitates in promoting the primary grain nucleation such as Al3Ti, Al3Er and Al3Sc, preventing the α-Al grain recrystallization such as Al3Cr and Al3Zr, and strengthening the matrix such as Al3Li and Al3Ni. Almost all of those experiments have been measuring the stable structures, and none of them have been focusing on the intrinsic properties of Al3X and their stabilities as a function of crystal structure and lattice constants due to the experimental limitations. In this study, the first-principle calculation is used to predict the metastablity of different Al3X structures including L12, DO22, DO23, DO19, DO18, DO24, R3̅m and P63/mmc. The varitions of lattice constant have been achieved by changing external pressure from 0 to 50 GPa. It was found that the L12 structure not only had a smaller lattice mismatch with α-Al, but also had a higher symmetry than the other structures, and the stability of the L12 structure was enhanced when external pressure was applied, and some other structures may undergo a transition to the L12 structure, while the elastic modulus of the L12 structure was improved. In addition, the elastic modulus of the Al3X precipitation phases of different structures was found to increase with decreasing distance between atomic pairs, and the distance between Al-X and X-X pairs had a much greater effect on the elastic modulus than the Al-Al pairs.