In this paper, the Fe-rich phases in and their detrimental effect on aluminum alloys are summarized. The existence of brittle platelet β-Fe-rich phases lowers the mechanical properties of aluminum ...

Removal of Iron From Aluminum: A Review

The Al−Fe and Al−Fe−Si particles formed during DC-casting of an Al-0.25 wt pct Fe-0.13 wt pct Si alloy have been examined. The particles were analyzed by transmission electron microscopy (TEM) and energy dispersive spectroscopy of X-rays (EDS). Crystal faults were studied by high resolution electron microscopy (HREM). Samples for electron microscopy were taken at various positions in the ingot,i.e., with different local cooling rates during solidification. At a cooling rate of 6 to 8 K/s the dominating phases were bcc α-AlFeSi and bct Al
 m
 Fe. The space group of bcc α-AlFeSi was verified to be Im3. Superstructure reflections from Al
 m
 Fe were caused by faults on {110}-planes. At a cooling rate of 1 K/s the dominating phases were monoclinic Al3Fe and the incommensurate structure Al
 x
 Fe. In Al3Fe, stacking faults on {001} were frequently observed. The structure of Al
 x
 Fe is probably related to Al6Fe. Some amounts of other phases were detected. For EDS-analysis, extracted particles mounted on holey carbon films were examined. Extracted particles were obtained by dissolving aluminum samples in butanol. Accurate compositions of various Al−Fe−Si phases were determined by EDS-analysis of extracted crystals.

Intermetallic phases formed during DC-casting of an Al−0.25 Wt Pct Fe−0.13 Wt Pct Si alloy

The status of rapid solidification is discussed in terms of recent progress in modelling methods of achieving solidification at high cooling rates and its effects on alloy constitution and microstructure. Applications currently in view are reviewed under the following headings: high-strength structural materials; tool and bearing materials; high-temperature materials, corrosion-resistant, catalytic and storage materials; and electrical and magnetic materials. It is concluded that the future of rapid solidification is not identifiable with any one process, activity or application and that many unresolved questions remain to challenge both the scientific and business communities.

The status of rapid solidification of alloys in research and application

The iron intermetallics observed in six dilute Al-Si-Fe alloys were studied using thermal analysis, optical microscopy, and image, scanning electron microscopy/energy dispersive X-ray, and electron probe microanalysis/wavelength dispersive spectroscopy (EPMA/WDS) analyses. The alloys were solidified in two different molds, a preheated graphite mold (600°C) and a cylindrical metallic mold (at room temperature), to obtain slow (}0.2 °C/s) and rapid (}15 °C/s) cooling rates. The results show that the volume fraction of iron intermetallics obtained increases with the increase in the amount of Fe and Si added, as well as with the decrease in cooling rate. The low cooling rate produces larger-sized intermetallics, whereas the high cooling rate results in a higher density of intermetallics. Iron addition alone is more effective than either Si or Fe+Si additions in producing intermetallics. The alloy composition and cooling rate control the stability of the intermetallic phases: binary Al-Fe phases predominate at low cooling rates and a high Fe:Si ratio; the β-Al5FeSi phase is dominant at a high Si content and low cooling rate; the α-iron intermetallics (e.g., α-Al8Fe2Si) exist between these two; while Si-rich ternary phases such as the δ-iron Al4FeSi2 intermetallic are stabilized at high cooling rates and Si contents of 0.9 wt pct and higher. Calculations of the solidification paths representing segregations of Fe and Si to the liquid using the Scheil equation did not conform to the actual solidification paths, due to the fact that solid diffusion is not taken into account in the equation. The theoretical models of Brody and Flemings[44] and Clyne and Kurz[45] also fail to explain the observed departure from the Scheil behavior, because these models give less weight to the effect of solid back-diffusion. An adjusted 500°C metastable isothermal section of the Al-Si-Fe phase diagram has been proposed (in place of the equilibrium one), which correctly predicts the intermetallic phases that occur in this part of the system at low cooling rates (}0.2 °C/s).

Iron intermetallic phases in the Al corner of the Al-Si-Fe system

Ultramicrotomy—a route towards the enhanced understanding of the corrosion and filming behaviour of aluminium and its alloys

A study was made on the formation of 'fir-tree' structure during D. C. casting of Al-Fe alloys. Al-Fe alloys containing 0.58%Fe and less than 0.01%Si were unidirectionally solidified. The alloys were also D. C. cast. The cooling rate during unidirectional solidification was measured by thermal analysis, while the cooling rate during D. C. casting was estimated through measurements of the dendrite arm spacing of the ingots. Identification of constituent phases were carried out by optional microscopy, electron microscopy and X-ray diffraction, and some of their chemical properties were discussed.The results obtained are summarized as follows:1) Al3Fe, Al6Fe and AlmFe (a body-centered tetragonal Al-Fe phase8)) were identified as secondary constituents. They were found to be formed in the following ranges of cooling rate:Al3Fe: less than 2°C/secAl6Fe: from 2 to 20°C/secb.c.t.AlmFe: more than 20°C/sec.2) Al3Fe and b.c.t. AlmFe were oxidized during anodizing in 15%H2SO4 solution, while Al6Fe did not undergo oxidation. Al3Fe and b.c.t. AlmFe were etched to appear dark-brown by 0.5%HF solution, while in the case of Al6Fe, only a slightly grey tint was detected.3) The microstructure of the D. C. cast ingots was divided into the four regions corresponding to different sizes of dendrite cells and to different constituent phases. The first, these cond and the third regions were outside the 'fir-tree' structure, while the fourth region was inside. Body-centered tetragonal AlmFe and a small amount of Al3Fe were secondary constituents in the first region which solidified very rapidly. Al3Fe phase existed in the second and third regions which solidified more slowly. Al6Fe phase was an interdendritic phase in the fourth region which solidified fairly fast.4) The cause of formation of 'fir-tree' structure seems to be attributable to the fact that the cooling rate during solidification varies from the surface to the center of D. C. cast ingots. In other words, the cause is likely attributed to macroscopic segregation of different types of intermetallic compounds.

https://www.jstage.jst.go.jp/article/jilm1951/25/2/25_2_48/_pdf

Al-0.6%Fe合金連続鋳造塊における樅ノ木組織の生成

Rapidly solidifed Al-0.6%Fe and Al-0.8%Fe-0.1%Mg alloys containing metastable Al6Fe and AlmFe were isochronally and isothermally heated at elevated temperatures. X-ray diffraction and optical and transmission electron microscopies were carried out on the phase change of these metastable phases. The metastable phases are directly transformed into stable Al3Fe not through any intermediate compound. The phase change mainly proceeds in the following process; that is, dissolution of the metastable phase in matrix and precipitation of Al3Fe phase at fresh sites of dendrite cell boundaries. The activation energy for the change is evaluated to be 70±10kcal/mol. The rate determining step of the change seems to be diffusion of Fe atoms in Al matrix.

/pdf/al-fehe-jin-niokeruzhun-an-ding-al-fexiang-nogao-wen-jia-re-4bgzmhkozu.pdf

Al-Fe合金における準安定Al-Fe相の高温加熱時の相変化

This study was made to investigate the change of "fir-tree" structure in D. C. cast Al-Fe-Si alloys during heating at elevated temperatures.The specimens used were Al-0.6%Fe and Al-0.6%Fe-0.1%Si alloy, some of which had been hot-rolled or cold-rolled. They were soaked at several temperatures of 560640°C.The experiments were carried out by anodizing, X-ray diffraction, optical microscopy, and electron microscopy.The results obtained were summarized as follows:(1) FeAl3 phase was present in the inner region of "fir-tree" structurs, while FeAl3 phase was found in the outer region. Another unknown phase would possibly be present in the outer region.(2) The "fir-tree" structure was eliminated by the transformation of FeAl6 into FeAl3 during heating at elevated temperatures.(3) The relation between the time required to eliminate the "fir-tree" structure and the reciprocal of the temperature conformed to Arrhenius' equation. The activation energy was evaluated to be 75 kcal/mol from the slope of the equation. The activation energy depended neither on the presence of 0.1%Si, nor on plastic deformation.(4) The following two processes were observed by heating thin foils in an elctron microscope.One was dissolution of FeAl6 phase in matrix and precipitation of FeAl3 phase on grain boundaries. The other was transformation of FeAl6 into FeAl3 in place, though the exact position of nucleation could not be determined.(5) Being derived from the above-mentioned activation energy, the rate determining step of the transformation seemed to be the diffusion of Fe or Al in the intermetallic compounds.

高温加熱時のAl-Fe-si合金中の縦ノ木組織の挙動

https://www.jstage.jst.go.jp/article/jilm1951/30/4/30_4_217/_pdf

小菅張弓

Papers

Al-0.6%Fe合金連続鋳造塊における樅ノ木組織の生成

Al-Fe合金における準安定Al-Fe相の高温加熱時の相変化

高温加熱時のAl-Fe-si合金中の縦ノ木組織の挙動

Al-Fe 系合金における金属間化合物

小菅 張弓

Papers

Al-0.6%Fe合金連続鋳造塊における樅ノ木組織の生成

Al-Fe合金における準安定Al-Fe相の高温加熱時の相変化

高温加熱時のAl-Fe-si合金中の縦ノ木組織の挙動

Al-Fe 系合金における金属間化合物

小菅張弓