Crystallographic studies on the iron-containing intermetallic phases in the 319-type aluminium casting alloys

Abstract

The iron-containing intermetallic compounds in type 319 aluminium casting alloys were investigated using convergent beam electron diffraction (CBED) and electron backscatter diffraction (EBSD). The Chinese script -phase was identified as having the cubic Im 3 space group consistent with the Al 19 Fe 4 MnSi 2 phase reported in the literature. However, the atomic ordering of this phase results in complex Kikuchi lines in the CBED and EBSD patterns, which makes phase and orientation identification difficult. In fact, it is shown that the EBSD patterns in the scanning electron microscope and Kikuchi patterns in the transmission electron microscope from this phase are closely related to the structurally similar m 3 5 icosahedral quasicrystals that form in numerous aluminium-transition metal alloys by both conventional and rapid solidification. The other iron-containing phase in these alloys was determined to be plate shaped and to have the orthorhombic Cmcm space group consistent with the -Al 5 FeSi phase, which has sometimes been confused with having a tetragonal or monoclinic structure. The nature of this structure is such that it frequently grows with a high density of faults that separate equivalent variants; these will be described and related to the previously incorrect interpretations of this being a tetragonal phase.

A Review of Transmission Electron Microscopy of Quasicrystals—How Are Atoms Arranged?

“…The CBED analysis on stable icosahedral Al-Cu-Fe reveals that it has a point group of m35 [70,71]. Such analysis on Al-Mn-Si [72], Al-Cu-Li [73] and Al-Si-Cu [74] icosahedral QCs, also indicates that these icosahedral QCs have a point group of m35. Actually, all the icosahedral QCs known to date are centrosymmetric and no icosahedral QCs with point group 235 have been found.…”

Mitigation of cylinder distortion in aluminum alloy engine blocks via heat treatment process optimization

“…In addition, the acicular morphology results in stress concentrations near the tips of the particles, which act as crack nucleation sites. For these reasons, the formation of β-Al 5 FeSi is highly deleterious to the mechanical properties of the 319 alloy [26][27][28][29]. To mitigate the detrimental effect of Fe, Mn is added, to suppress the formation of Although the α-Al 15 (Fe,Mn) 3 Si 2 phase is also a hard and brittle intermetallic phase, its more compact morphology reduces the stress concentration at the particle-matrix interface, which improves the mechanical properties of the 319 Al alloy relative to the Mn-free alternatives [26][27][28][29].…”

“…For these reasons, the formation of β-Al 5 FeSi is highly deleterious to the mechanical properties of the 319 alloy [26][27][28][29]. To mitigate the detrimental effect of Fe, Mn is added, to suppress the formation of Although the α-Al 15 (Fe,Mn) 3 Si 2 phase is also a hard and brittle intermetallic phase, its more compact morphology reduces the stress concentration at the particle-matrix interface, which improves the mechanical properties of the 319 Al alloy relative to the Mn-free alternatives [26][27][28][29]. The studies of Hwang et al [26] and Narayanan et al [27] found that the ideal Fe:Mn concentration ratio to improve mechanical properties in Al-Si alloys ranged between 0.75:1 and 1.5:1.…”

“…The morphology of the Al-Si eutectic for the billets solutionized at 515 and 530 °C was investigated using optical microscopy and is shown in As reviewed in Section 2.3.1.1, modification of eutectic Si is achieved through fragmentation followed by spheroidization and coarsening of the particles. Heat treatment temperature is an important factor since the processes governing Al-Si eutectic modification are highly dependent on diffusion rate [10,20,28,[31][32][33][34]. For this reason, the observed trends where solutionizing temperatures above 515 °C had coarser and more spherical Si particles while temperatures below 515 °C showed varying degrees of Si particle fragmentation and spheroidization was expected.…”

Chinese Script vs Plate-Like Precipitation of Beta-Al9Fe2Si2 Phase in an Al-6.5Si-1Fe Alloy

“…Later work by Hwang et al [17] argues that this latter hypothesis was a misperception of crystal structure, so that the monoclinic structure will be accepted here.…”