Formation Of Fe-rich Phases Research Articles

Microstructure and Tensile Strength of an Al-Si-Fe-V Alloy: Vanadium and Solidification Thermal Parameters as Recycling Strategies

One of the greatest challenges facing the recycling of Al-based alloys is handling Fe incorporation. The formation of Fe-rich phases has negative impacts on the mechanical behavior and may limit the usage of recycled alloys. In this context, V addition is regarded as a potential solution since it can inhibit the formation of such phases. However, the microstructure evolution of V-modified Al-based alloys is not fully understood, especially when different solidification cooling regimes are considered. Thus, this work investigates the microstructure and tensile properties of an Al-7Si-1Fe [wt.%] alloy modified with a 0.5 wt.%V addition. Directionally solidified samples were produced and subjected to microstructure analysis and tensile tests. It was found that the addition of V reduces the fraction of β-AlFeSi particles because of the formation of new V-rich phases. This was determinant to improve the tensile properties for faster cooling conditions during solidification. For moderate and slow cooling regimes, however, the V-containing alloy had a less favorable mechanical behavior due to the formation of larger β-AlFeSi particles. Finally, quantitative relationships are proposed for the prediction of tensile properties from microstructural parameters using multiple linear regression analysis.

Effect of B addition on the formation of Fe-rich phases in Al-Si-Fe alloys

Boron (B) is an effective grain refiner in Al-Si alloys, but the mechanism responsible for the effect of B on the formation and growth of Fe-rich phases is still in debate. In this paper, we used in-situ synchrotron X-ray radiography, combined with optical microscopy, scanning electron microscopy, thermodynamics and first-principles calculations, to study the influence of B on the nucleation and growth of Fe-rich phases in Al-7Si-xFe (x = 1.2–3.0) alloys. The results showed that B had an excellent influence on the grain refinement of Al-7Si-1.2Fe alloys, but it had no obvious effect on the morphology and distribution of Fe-rich phases due to the eutectic reaction to form Al-AlB2. B had a certain refining effect on primary Fe-rich phases in Al-Si-Fe alloys with high Fe content (≥2.36 wt. %), but it cannot completely inhibit the formation of these plate-like Fe-rich phases. The in-situ synchrotron X-ray radiography results showed that the addition of B significantly reduced the formation temperature of primary Fe-rich phases. First-principles calculations showed that the adsorption energy of B on the nucleation sites , e.g., α-Al2O3 (0001), was significantly higher than that of Fe, which inhibited the nucleation of the primary Fe-rich phase above the Al-AlB2 eutectic temperature and promoted its undercooling of nucleation. Furthermore, many α-Al nuclei formed during the transition to the Al-AlB2 eutectic; their subsequent growth hindered the development of the primary Fe-rich phase. The results of this study provide insights for designing new recycled Al-Si alloys and fundamental knowledge of Fe-rich phase modification by B addition.

Effect of B Addition on the Formation of Fe-Rich Phases in Al-Si-Fe Alloys

Effect of B Addition on the Formation of Fe-Rich Phases in Al-Si-Fe Alloys

Elimination of Iron Based Particles in Al-Si Alloy

Abstract This paper deals with influence on segregation of iron based phases on the secondary alloy AlSi7Mg0.3 microstructure by chrome. Iron is the most common and harmful impurity in aluminum casting alloys and has long been associated with an increase of casting defects. In generally, iron is associated with the formation of Fe-rich phases. It is impossible to remove iron from melt by standard operations, but it is possible to eliminate its negative influence by addition some other elements that affect the segregation of intermetallics in less harmful type. Realization of experiments and results of analysis show new view on solubility of iron based phases during melt preparation with higher iron content and influence of chrome as iron corrector of iron based phases. By experimental work were used three different amounts of AlCr20 master alloy a three different temperature of chill mold. Our experimental work confirmed that chrome can be used as an iron corrector in Al-Si alloy, due to the change of intermetallic phases and shortening their length.

Effect of Manganese on the Formation of Fe-rich Phases in Electromagnetic Stirred Hypereutectic Al-22Si Alloy with 2 % Fe

The effect of Mn on the microstructure of electromagnetic stirred hypereutectic Al-22Si-2Fe (% w/w) alloys was studied. The results show that the alloy with a Mn/Fe ratio zero, contained plentiful α-Al4FeSi2 phases existing as mainly intermetallic compounds in the solidified microstructures by electromagnetic stirring (EMS) process. With EMS process, the alloy with 0.61 % Mn contained acicular β-Al5(Fe, Mn)Si, δ-Al4(Fe, Mn)Si2 and blocky α-Al15(Fe, Mn)3Si2 phases in the solidification microstructure of the stirred A1 alloy. As the Mn/Fe ratio increased to 1, intermetallic compounds were mainly in the form of blocky and fine α-Al15(Fe, Mn)3Si2 phases in the microstructure. The intermetallic compounds were examined with an optical microscope, scanning electron microscope, and X-ray diffraction. The acicular δ-Al4(Fe, Mn)Si2 and blocky α-Al15(Fe, Mn)3Si2 phases were also analyzed by transmission electron microscopy.

Distribution of Fe-rich phases in eutectic grains of Sr-modified Al–10 wt.% Si–0.1 wt.% Fe casting alloy

The addition of Sr to Al–Si-based alloys is known to modify the morphology of the eutectic Si phase and to influence the nucleation of eutectic grains. Understanding the distribution and the morphology of small constituent phases in eutectic grains such as Fe-rich intermetallic phases can further yield an insight into the cellular substructure of eutectic grains formed during solidification. The addition of 200ppm Sr to an Al–10Si–0.1Fe alloy and its influence on the formation of Fe-rich phases was comprehensively studied by several microscopy techniques. Optical microscopy combined with scanning electron microscopy revealed the existence of two types of Fe-rich phases at cell boundaries of eutectic grains. The Fe-rich phases were identified as α-Al14Fe3Si2 and δ-Al4FeSi2 by transmission electron microscopy. Both Fe-rich phases are located at distinct regions in the eutectic grain, namely in the transition region (region 2: α-phase) and the outer region (region 3: δ-phase) of the eutectic grain. The three-dimensional morphology of the eutectic Si phase and the Fe-rich phases at the eutectic cell boundaries was investigated by focused ion beam tomography. The Fe-rich α-phase was found to form concentrated networks with the 3D morphology of “sheets”, whereas the Fe-rich δ-phases exist as thin platelets. The distribution of Fe-rich phases in the cellular substructure of eutectic grains are described on the basis of the evolution of the eutectic solidification front by a qualitative solidification model.

Mineralogical reactions in the Tournemire argillite after in-situ interaction with steels

Steels are possible materials for high level radioactive waste containers used in long term geological disposal in argillaceous environments. Under chemical conditions of a deep repository, the release of iron from these canisters could modify the properties of clay minerals. Thereby, many batch experiments have been realized on argillite under disposal conditions. The French Institute of Radioprotection and Nuclear Safety conducts an experimental program on steel/argillite interactions in underground natural conditions in its Tournemire experimental site (Aveyron, France). In order to determine these interaction processes, the present study focuses both on petrography and mineralogy characterization of modifications in the argillite in contact with steel samples. The accurate study of the argillite and steels after 6 years of contact indicates no significant changes for the argillite in contact with the stainless steels. For the argillite in contact with the carbon steels both numerous steel corrosion evidences and clear textural, petrographic, mineralogical and chemical modifications of the initial nature of the argillite are observed. The Fe°/argillite contacts indicate the development of a Fe-rich front within the argillite resulting from the iron diffusion from the corroded steel and which is connected with mineralogical changes of the initial argillite. This Fe-enrichment is accompanied by crystallization of significant amounts of goethite/lepidocrocite (FeOOH) and some traces of magnetite near the steel surface. The formation of Fe-rich phases within the argillite is associated with dissolution–crystallization processes. Thus, after bulk sample XRD and SEM data, these processes consist in dissolution of calcite, phyllosilicate (I/S) and pyrite and crystallization of some traces of gypsum and melanterite.

Phase-dependent distribution of Fe-rich nanocrystals in MOVPE-grown (Ga,Fe)N

We present a detailed transmission electron microscopy study of the structure and distribution of self-organized Fe-rich nanocrystals in (Ga,Fe)N grown via metal-organic vapor phase epitaxy (MOVPE). In samples with a concentration of magnetic ions above the solubility limit— x ⩾ 0.4 % —of Fe in GaN at the growth conditions we can identify three different phases of the Fe-rich enclosures, namely: (a) α -Fe segregated in proximity of the surface, (b) ε -Fe 3N in the volume beneath, though well above the nominal interface between the undoped GaN buffer and the Fe-doped overlayer, and (c) nanocrystals at an intermediate location showing the presence of adjacent α -Fe and ε -Fe 3N. These observations suggest that nitrogen evaporation at the growing surface play an important role in the formation of Fe-rich phases. The occurrence of α -Fe and ε -Fe 3N in the same nanocrystal indicates that the two phases are actually correlated: phase separation may first lead to the precipitation of ε -Fe 3N, which inherits the hexagonal structure of GaN but generates misfit dislocations, and then a further depletion of nitrogen promotes the conversion of ε -Fe 3N into α -Fe.