Morphology, thermal stability, electronic structure and mechanical properties of α-AlFeMnSi phases with varying Mn/Fe atomic ratios: Experimental studies and DFT calculations

Abstract

Separation of Fe-containing intermetallics is an effective method to decrease Fe content in Al-Si alloys. The three-dimensional (3D) morphology and stability of Fe-containing intermetallics are important parameters affecting their separation efficiency. Combined with experiments and first-principles calculations, the variation of 3D morphology, stability, electronic structure and mechanical properties of α-AlFeMnSi are studied with the evolution of Fe/Mn atomic ratio. The experimental results show that the 3D morphology of α-AlFeMnSi transforms from Chinese character to regular polyhedron with the increment of Mn/Fe atomic ratio and all α-AlFeMnSi phases have cubic crystal structure. The calculated mixing enthalpies indicate that all α-AlFeMnSi phases are stable in thermodynamics due to the negative values. The electronic structure and Mulliken population calculations show that the variation of Mn/Fe ratio results in the overall change of chemical bondings of Si-Mn, Si-Fe, Al-Mn and Al-Fe, which leading to the evolution of stability and mechanical properties of α-AlFeMnSi phases. The calculated results of mechanical properties demonstrate that the Young’s modulus and hardness of α-AlFeMnSi phases are improved with the increment of Mn/Fe atomic ratio, which is also validated by nano-indentation measurements. These results provide the componential guidance about designing easy-separable Fe-containing intermetallics and try to explain physical mechanism of property evolution of α-AlFeMnSi phase.