Unraveling Site‐Occupancy Mechanisms, Stability, and Mechanical Properties of Fe/Cr/V‐Doped Orthorhombic Cmcm‐Al6Mn Intermetallic: A First‐Principles Study

Abstract

As a pivotal secondary phase governing microstructure evolution and mechanical performance of Al–Mn wrought alloys, Al6Mn intermetallic is constrained by its intrinsic brittleness, which impedes further property improvement of the alloy system. First‐principles calculations within the density functional theory framework are conducted to systematically elucidate the sublattice site preferences of Fe, Cr, and V in orthorhombic Cmcm‐Al6Mn, as well as their modulation effects on structural stability and mechanical behavior. Fe is found to preferentially occupy the Mn sublattice, while both Cr and V favor Al3 sites. All doping configurations maintain thermodynamic stability with negative formation enthalpies. The three preferred configurations concurrently satisfy the mechanical Born criteria and dynamic stability, free of imaginary phonon frequencies, whereas Fe substitution at Al1/Al2 sites induces pronounced imaginary frequencies and dynamic instability. Low‐concentration doping exerts negligible influence on bulk modulus, but tailors ductile‐brittle characteristics by tuning shear‐direction covalent bonding. Fe–Mn substitution yields notable toughening effects, V‐Al3 retains the highest stiffness, and non‐preferential sites display extreme performance divergence. d‐Orbital hybridization underpins the occupancy tendency and property evolution, offering theoretical guidance for microalloying design of Al–Mn alloys.