Microstructural Characterization and Phase Diagram Calculation of a Less Known Al–Fe–Mn–Si Phase in a SiC_p/2014Al Composite

Abstract A systematic characterization of a less known Al, Fe, Mn, and Si phase in a SiC particulate-reinforced 2014Al composite (SiC_p/2014Al) was performed. In addition to the expected CuAl₂ phase, the Al, Fe, Mn, and Si phase was formed as either an adhesion (>1 µm) onto SiC in the as-cast composite, or as a precipitate (<100 nm) in the matrix after hot extrusion. The structure of the phase was identified as cubic by both X-ray diffraction and selected area electron diffraction (SAED). The SAED pattern also indicated that the structure belongs to the Pm$\bar{3}$ space group instead of Im$\bar{3}$. The thermodynamic phase diagram was calculated, confirming the presence of an α-AlFeMn or α-AlFeSi phase in the Al–Fe–Mn and Al–Fe–Si ternary systems, respectively, within the Fe, Mn, and Si content range corresponding to 2014Al. Wavelength-dispersive spectroscopy analysis indicated that the composition of the phase is close to Al₁₂(Fe, Mn)₃Si₂, in which the Mn/Fe ratio is in the range of 0.6–1.4. The determined Mn/Fe ratio corresponds to the nominal composition of Mn and Fe in the alloy.