Exploring crystal structures, stability and mechanical properties of Fe, Mn-containing intermetallics in Al-Si Alloy by experiments and first-principles calculations

Abstract

Separation of Fe-containing intermetallics is an effective method to decrease Fe content in Al-Si alloys. Regular morphology and higher precipitation temperature are necessary for physical separation of Fe-containing phases. So far, there have been few studies about the three-dimensional (3D) morphology evolution, crystal structure variation and physical mechanism for the precipitation temperature improvement of Fe-containing phases. Combined with experiments and first-principles calculations, the effects of Mn on 3D morphology, crystal structure and precipitation temperature of Fe-containing phases are systematically investigated. The DSC and first-principles calculations show that the precipitation temperature of Fe-containing phase improves prominently after the addition of Mn and the high precipitation temperature of α-AlFeMnSi attributes to its stronger chemical bonding strength of Mn-Si validated by binding energy and Mulliken population analysis, which also leads to high Young’s modulus and hardness of α-AlFeMnSi. It demonstrates that the crystal structure of Fe-containing intermetallics is transformed from monoclinic β-AlFeSi to cubic α-AlFeMnSi and the morphology changes from plate-like to dodecahedron shapes.