Effects of Si solution in θ-Al13Fe4 on phase transformation between Fe-containing intermetallic compounds in Al alloys

Abstract

θ-Al13Fe4 is one of the common Fe-containing intermetallic compounds (FIMCs) that forms during solidification in Al alloys. Silicon (Si) as impurity or solute in Al alloys is easily doped into θ-Al13Fe4, which not only causes compositional variation but also modifies the lattice parameters, and in some circumstances, modifies or changes the crystal structure of θ-Al13Fe4. In this study, multiple Al-Fe and Al-Fe-Si alloys which solidified θ-Al13Fe4 as equilibrium or non-equilibrium phase in primary or eutectic structures were designed and investigated. Different types of phase transformation among θ-Al13Fe4 and the other FIMCs such as α’-Al8Fe2Si, α-Al15(Fe,Mn)3Si2 and β-Al5FeSi were investigated with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and single crystal X-ray analysis. The composition and lattice parameters of FIMCs observed in this study were measured by TEM and X-ray analysis. The orientation relationships between θ-Al13Fe4 and the other types of FIMCs (α’-Al8Fe2Si, α-Al15(Fe,Mn)3Si2 and β-Al5FeSi) were determined with TEM analysis. The phase selection and solidification sequence were investigated by comparing the phase diagram calculation and the casting experiments. The configuration entropy of FIMCs was calculated to build up structural models. Finally, the influence of incorporation of Si into θ-Al13Fe4 on the phase transformation between θ-Al13Fe4 and the other types of FIMCs were discussed from crystallographic and thermal stability perspectives.