First-principles study of structural, mechanical, and electronic properties of typical iron-containing phases in Al-Cu alloys under different pressures

Highlights: • Properties of Al₃Fe, Al₆Fe, & Al₇Cu₂Fe in Al-Cu alloys were studied. • First-principles calculation were conducted due to the complex structure of the phases and difficulties in obtaining single crystal. • Al₆Fe has lowest alloying ability and a high cooling rate is needed to form Al₆Fe. • Al₆Fe is most ductile but crack initiation occurs due to its highest anisotropy. • The component design during solidification can be optimized to improve mechanical properties through the calculation. -- Abstract: The structural, mechanical, and electronic properties of typical iron-containing phases, Al₃Fe, Al₆Fe, and Al₇Cu₂Fe, in Al-Cu alloys were determined using first-principles calculations. The calculated lattice constants were in good agreement with experimental values. Al₃Fe exhibited the highest structural stability and most superior alloying ability. Al₆Fe had the worst alloying ability and required a high cooling rate for its formation during solidification. Al₇Cu₂Fe was the easiest to dissolve into the Al matrix because it has the lowest negative cohesion energy. Mechanical properties improved with increasing pressure. Al₃Fe exhibited the highest stiffness and strongest resistance to volume change and shear deformation. Al₆Fe had better ductility owing to the high bulk-to-shear modulus ratio and Poisson's ratio; however, it had the lowest hardness and highest anisotropy, leading to a strong tendency for crack initiation. Density of states data showed that no structural variation or phase transformation occurs for any of the phases under applied pressure; moreover, they indicated covalent bonding in Al₃Fe, accounting for the relatively high structural stability. Finally, all iron-containing phases were confirmed to be paramagnetic.