Fe-Al Alloys Research Articles

Influence of rare earth cerium on the microstructures and performances of Al-Fe alloy

Influence of rare earth cerium on the microstructures and performances of Al-Fe alloy

Effects of Hot Extrusion Temperature Conditions on the Hardness and Electrical Conductivity of Rapidly Solidified Al-Fe Alloys.

Rapidly solidified Al-Fe alloys produced by hot extrusion are a promising replacement for copper-based electrical conductors because of their light weight. However, the effects of the extrusion temperature conditions on the mechanical and electrical properties of extruded materials are unknown. The present work investigated the effects of billet preheating temperature, in situ temperature during extrusion, and additional heat treatment after extrusion on hardness and electrical conductivity. An air-jet atomized Al-2.3%Fe alloy powder was pre-sintered into cylindrical billets and then hot-extruded. The hardness of the extrudates decreased as the in situ temperature during extrusion increased above 650 K. The billet preheating temperature affected the in situ temperature during extrusion. Additional annealing after extrusion decreased the hardness. The cause of the decrease in hardness was coarsening of the grain of the aluminum matrix. The electrical conductivity increased with higher billet preheating temperatures before extrusion or additional annealing after extrusion; however, an in situ temperature rise for a few seconds during extrusion did not affect the conductivity. The increase in electrical conductivity was considered to be caused by a decrease in the amount of solute iron, which requires holding the material at a high temperature for longer than several minutes.

Effect of friction stir processing on microstructure, mechanical, and damping properties of Al-5Fe alloy

The effect of friction stir processing (FSP) on the microstructure, mechanical properties, and damping properties of as-cast Al-5Fe alloy was investigated. The results showed that the needlelike or rod-like eutectic Fe-rich phases were broken into fine particles and homogeneously distributed on the Al matrix with fine equiaxed recrystallized grains with the size of 2–5 μm in the stir zone after FSP. The hardness distribution in the as-cast alloy is highly dispersed. The strength, ductility increased simultaneously after FSP. The increase in the tensile strength values was about 15.6% after FSP. The FSPed alloy exhibited higher elongation to fracture of about 27.5% in comparison with the as-cast sample having only 3.7%. Meanwhile, FSP can obviously improve the damping properties of the Al-5Fe alloy.

The mechanism of Fe-rich intermetallic compound formation and growth on inoculants revealed by electron backscattered diffraction and X-ray imaging

Fe-rich intermetallics affect critically the mechanical properties and recyclability of aluminium alloys. Increasing effort has been spent on the inoculation of these intermetallics, hoping to promote a finer distribution. Recently Al-5Ti-1B (wt.%), originally developed to refine α-Al, has been shown to refine Al13Fe4, an intermetallic phase present in a variety of Al alloys. However, mechanisms of the formation and growth of the intermetallics on the inoculants are unclear. In this paper, Ti is added to Fe-containing Al alloys to produce a large number of potent Al3Ti particles, the active inoculant in Al-5Ti-1B. We use a combination of electron backscattered diffraction, in situ synchrotron X-ray radiography and post-solidification X-ray computed tomography to investigate the formation and growth of primary Al13Fe4 on Al3Ti inoculants, first in a model Al-Fe alloy, with key insights then confirmed in a high Fe-containing, recycled 6xxx alloy. Crystallographic orientation relationships between Al13Fe4 and Al3Ti are analysed comprehensively, and the formation and growth dynamics of Al13Fe4 on Al3Ti is also unveiled. A strong link is revealed between the formation of Al13Fe4 on Al3Ti and a twinning-related pseudo-symmetry of Al13Fe4. Finally, a potential strategy to refine both intermetallics and α-Al in recycled alloys with elevated Fe concentration is proposed.

Beyond the Parallel Tangent Method to Predict the Composition of the First Nucleating Phase from Oversaturated Solutions

The parallel tangent method widely applied to predict the composition and driving force to form a nucleus from an oversaturated solution is extended in this paper. The parallel tangent method is shown to (i) Over-estimates the composition difference between the first nucleus and the parent phase, (ii) Neglects the composition dependence of interfacial energies and (iii) Neglects the composition dependence of probability to form embryos prior to nucleation. New model equations are developed here for the composition dependence of the interfacial energies and probability to form the embryos as function of nucleus composition at given matrix composition. The most probable composition of the first nucleus is found at the maximum of the driving force of nucleation extended by the new model equations. The success of the extended method is demonstrated for an Al-Fe liquid alloy with 0.3 w% of Fe to predict the first nucleating intermetallic phases upon cooling after nucleation of the fcc phase. It is shown that although the prediction based on the parallel tangent method contradicts experimental observations, the prediction based on our extended method agrees with them.Graphical

Fabrication of Fe–30Al alloy using plasma arc welding powered twin-wire directed energy deposition-arc process: Droplet transfer, microstructure, and mechanical property investigation

Intrinsic brittleness and cold cracking sensitivity of Fe–Al intermetallic compounds make their fabrication and processing difficult. In recent years, an innovative additive manufacturing (AM) technology, twin-wire directed energy deposition-arc (TW-DED-arc), has been developed to prepare defect-free Fe–Al alloys via in-situ alloying of Fe and Al elements in a gas tungsten arc welding (GTAW) generated molten pool. However, unconstrained plasma of regular tungsten arc leads to excessive heating area and residual stress during AM buildup. And relatively weak arc pressure of GTAW makes composition inhomogeneity a concern in the in-situ alloying molten pool. To solve the two potential drawbacks, plasma arc welding (PAW) possessing higher energy density and arc pressure is used to power the TW-DED-arc process and fabricate Fe–30Al alloy. In the present research, a special wire-feeding strategy for stable twin-wire feeding of Fe and Al wires is successfully developed to overcome the droplet transfer difficulty induced by constrained arc of PAW and large thermophysical properties difference of heterogeneous filler wires. And according to microscopy characterization results, the innovative PAW powered TW-DED-arc process is capable of fabricating defect-free Fe–30Al bulk sample with homogeneous Al content and epitaxial columnar grain structures. The successful application of PAW-powered TW-DED-arc technique in fabrication of iron aluminide provides stabler and more efficient route for iron aluminide component.

Microstructure and Mechanical Properties of a Precipitation‐Strengthened Fe–Al–Nb Alloy

Fe–Al alloys provide an attractive property profile for applications at temperatures of up to 700 °C. Herein, a Fe–25Al–2Nb (at%) alloy is, manufactured on an application‐relevant scale. Preforms are cast and subsequently forged into a turbine blade shape. The microstructural evolution and mechanical properties, namely quasistatic strength and creep response, are tested in different manufacturing conditions and are compared to the properties of equilibrated laboratory alloys, as well as to literature results. The cast process leads to coarse‐grained initial nonequilibrium microstructures with lower amounts of Laves phase as compared to thermodynamic equilibrium. Forging at 900 °C leads to the significant formation of subgrains in the Fe–Al matrix and precipitation of the Laves phase. The as‐cast condition of Fe–25Al–2Nb exhibits a complex creep behavior governed by the transient formation of a coherent Heusler phase as well as Laves phase formation and recrystallization in later stages of creep. In the forged condition, the material behaves similarly to long‐term annealed material. Although Fe–25Al–2Nb has slightly lower strength and lower creep resistance over the entire temperature range tested, it performs well compared to Ta‐containing Fe–Al alloys due to its lower cost and density.

Microstructural evolution and superior properties of conductive Al–Fe alloy processed by ECAP

The new conductive Al–Fe alloy (AA8176) is used in power transmission due to its high electrical conductivity. As a non-agе-hardenable alloy, Al–Fe alloy is not a subject for the strength improvement. So, Equal-channel Angular Pressing (ECAP) is introduced to try to develop the advanced Al–Fe alloy with improved mechanical performance and good electrical conductivity. After different number of passes at room temperature, its electrical conductivity is maintained at quite high value (>60% IACS), close to that of pure aluminum, and its change during ECAP processing is insignificant. At the same time, the yield strength increases sharply from 46 MPa to a nearly 200 MPa after 8 passes. Elongation to failure also increases to 11% with increasing the number of passes. Superior combination of strength and electrical conductivity was demonstrated in alloys subjected to ECAP. Also, the study of microstructural evolution with a close attention to the evaluation of grain size, misorientation angle, size and distribution of Al–Fe intermetallic particles was performed. ECAP shows different advantages and potential in Al–Fe alloy performance improvement by achieving the ultra-fined grains and high-density dislocations through the imposed strain, instead of the formation of abundant precipitates in alloys through traditional heat treatment.

Electrochemical separation of Fe(III) impurity from molten MgCl2-NaCl-KCl for magnesium electrolytic production

To effectively separate Fe(III) impurity and purify the electrolyte for magnesium electrolytic production, the electrochemical behavior of Fe(III) on tungsten electrode was systematically examined in molten MgCl2-NaCl-KCl. Fe(III) ions can stably exist in the melt at 700 °C. Fe(III) undergoes a one-step reduction to iron metal on tungsten electrode exchanging three electrons, and the reaction process is reversible and controlled by diffusion. The deposition of iron on tungsten electrode belongs to the progressive nucleation mode. The co-reduction of Fe(III) and Al(III) makes the reduction of Al(III) at a more positive potential via formation of Al-Fe alloy. By electrolysis at −1.5 V in molten MgCl2-NaCl-KCl-0.94 wt%FeCl3-1.04 wt%AlCl3 for 8 h, Fe(III) and Al(III) impurities can be efficiently separated from the melt as AlFe3 and Fe, and the contents of FeCl3 and AlCl3 in the electrolyte can be reduced to a fairly low level of 0.022 wt% and 0.037 wt%, respectively. It is confirmed that the Fe(III) impurity in the electrolyte has a detrimental effect on the aggregation properties and purity of the magnesium metal generated during electrolysis. When electrolysis in the electrolyte purified by pre-electrolysis, the generated liquid magnesium metal can converge together and its purity can improved from 99.48% to 99.88% compared with direct electrolysis in the electrolyte with higher concentration of Fe(III) and Al(III) impurities. Molten salt pre-electrolysis is proven to be a practically effective method to purify the MgCl2-NaCl-KCl electrolyte for magnesium electrolytic production.

The Effect of Casting Technique and Severe Straining on the Microstructure, Electrical Conductivity, Mechanical Properties and Thermal Stability of the Al-1.7 wt.% Fe Alloy.

This paper features the changes in microstructure and properties of an Al-Fe alloy produced by casting with different solidification rates followed by severe plastic deformation and rolling. Particularly, different states of the as-cast Al-1.7 wt.% Fe alloy, obtained by conventional casting into a graphite mold (CC) and continuous casting into an electromagnetic mold (EMC), as well as after equal-channel angular pressing and subsequent cold rolling, were studied. Due to crystallization during casting into a graphite mold, particles of the Al6Fe phase are predominantly formed in the cast alloy, while casting into an electromagnetic mold leads to the formation of a mixture of particles, predominantly of the Al2Fe phase. The implementation of the two-stage processing by equal-channel angular pressing and cold rolling through the subsequent development of the ultrafine-grained structures ensured the achievement of the tensile strength and electrical conductivity of 257 MPa and 53.3% IACS in the CC alloy and 298 MPa and 51.3% IACS in the EMC alloy, respectively. Additional cold rolling led to a further reduction in grain size and refinement of particles in the second phase, making it possible to maintain a high level of strength after annealing at 230 °C for 1 h. The combination of high mechanical strength, electrical conductivity, and thermal stability can make these Al-Fe alloys a promising conductor material in addition to the commercial Al-Mg-Si and Al-Zr systems, depending on the evaluation of engineering cost and efficiency in industrial production.

EVALUATION OF THE WEAR OF AN FE-AL ALLOYTURBOCHARGER ROTOR SEAL RING UNDER SELECTEDOPERATING CONDITIONS

This publication presents the possibility of extending the service life of the rotor shaft seal ring in an automotiveturbocharger by using an intermetallic Al-Fe alloy. Comprehensive results of tribological, metallographic andprofilometric tests of this alloy (vacuum cast) operating in a sliding association on a T-05 bench allowedthe representation of a real friction node. Based on empirical tests, it will be possible to determine whichalloy (Al-Fe alloy or the one currently used for sealing rings of a car turbocharger rotor shaft) has bettertribological properties. For this purpose, the research was based on an experiment that assumes three mainfactors determining the wear of the tested association. The result of the experimental plan was to obtain threedimensionaldiagrams showing the influence of the wear factors on the friction force and surface topography.

The Mechanism of Dendrite Formation in a Solid-State Transformation of High Aluminum Fe-Al Alloys.

The mechanism of solid-state dendrite formation in high-aluminum Fe-Al alloys is not clear. Applying an in-situ observation technique, the real-time formation and growth of FeAl solid-state dendrites during the eutectoid decomposition of the high-temperature phase Fe5Al8 is visualized. In-situ experiments by HT-CSLM reveal that proeutectoid FeAl usually does not preferentially nucleate at grain boundaries regardless of rapid or slow cooling conditions. The critical radii for generating morphological instability are 1.2 μm and 0.9 μm for slow and rapid cooling, respectively. The morphology after both slow and rapid cooling exhibits dendrites, while there are differences in the size and critical instability radius Rc, which are attributed to the different supersaturation S and the number of protrusions l. The combination of crystallographic and thermodynamic analysis indicates that solid-state dendrites only exist on the hypoeutectoid side in high-aluminum Fe-Al alloys. A large number of lattice defects in the parent phase provides an additional driving force for nucleation, leading to coherent nucleation from the interior of the parent phase grains based on the orientation relationship {3¯30}Fe5Al8//{1¯10}FeAl, <111¯>Fe5Al8//<111¯>FeAl. The maximum release of misfit strain energy leads to the preferential growth of the primary arm of the nucleus along <111¯> {1¯10}. During the rapid cooling process, a large supersaturation is induced in the matrix, driving the Al atoms to undergo unstable uphill diffusion and causing variations in the concentration gradient as well as generating constitutional undercooling, ultimately leading to morphological instability and the growth of secondary arms.

Modification mechanisms of hypereutectic Al-Fe alloys treated by Sm/Yb addition: Experiments and first-principles calculations

The effects of Sm/Yb on the microstructure, electrical conductivity (EC), thermal conductivity (TC) and thermal expansion properties of hypereutectic Al-Fe alloys were investigated by combining experiments and first-principles calculations. The microstructure evolution shows that the addition of Sm/Yb can effectively modify the primary Al13Fe4 phase, observing the best modification effect with 0.5 % Sm and 0.3 % Yb addition. Besides, adding Sm/Yb can simultaneously improve the EC, TC and thermal expansion performance of hypereutectic Al-Fe alloys. The improvement of thermal-physical properties is mainly due to the fact that the coarse primary Al13Fe4 intermetallic phase is modified to fine and star-like particles, which reduces the scattering of electrons and phonons. The first-principles calculation results show that both Sm/Yb can be stably adsorbed on the P1 terminal Al13Fe4 (010) surface, then inhibits the preferential growth of primary Al13Fe4 phase. The theoretical calculations and experimental results confirm that adsorption and constitutional undercooling are the main reasons for Sm/Yb modification. This study shows that rare earth elements modification is an effective method to control the morphology of primary phase and improve the thermal-physical properties of hypereutectic Al-Fe alloys.

Fabrication of a Porous Fe–Al Intermetallic Alloy with Ultrahigh Open Porosity

Herein, a porous Fe–Al intermetallic material with ultrahigh open porosity is prepared via the multistep sintering process using a Fe–Al–Mn powder mixture as the raw material. The microstructure, phase composition, Mn sublimation, and open porosity of the sintered Fe–Al–Mn compacts are investigated. The compacts sintered at temperatures ≤700 °C are composed of the newly formed Fe/Mn‐based solid solutions, intermetallic phases, and the original elemental particles without the sublimation of Mn. The open porosities of the 650‐ and 700 °C‐sintered compacts are ≈39.83 and ≈47.19 vol%, respectively. After sintering at 1250 °C, Mn is rarely left in the porous body, and a single Fe–Al intermetallic phase with an even chemical composition is generated. The open porosity of the 1250 °C‐sintered compacts is ≈66.67 vol%, superior to other reported porous Fe–Al materials, and its strength is ≈22.5 MPa, which is competitive as well. This work may open a new strategy to design and optimize the high‐quality porous Fe–Al alloy in future.

Anelastic Effects in Fe-Ga and Fe-Ga-Based Alloys: A Review.

Fe-Ga alloys (GalFeNOLs) are the focus of attention due to their enhanced magneto-elastic properties, namely, magnetostriction in low saturation magnetic fields. In the last several years, special attention has been paid to the anelastic properties of these alloys. In this review, we collected and analyzed the frequency-, amplitude-, and temperature-dependent anelasticity in Fe-Ga and Fe-Ga-based alloys in the Hertz range of forced and free-decay vibrations. Special attention is paid to anelasticity caused by phase transitions: for this purpose, in situ neutron diffraction tests with the same heating or cooling rates were carried out in parallel with temperature dependencies measurements to control ctructure and phase transitions. The main part of this review is devoted to anelastic effects in binary Fe-Ga alloys, but we also consider ternary alloys of the systems Fe-Ga-Al and Fe-Ga-RE (RE-Rare Earth elements) to discuss similarities and differences between anelastic properties in Fe-Ga and Fe-Al alloys and effect of RE elements. We report and discuss several thermally activated effects, including Zener- and Snoek-type relaxation, several transient anelastic phenomena caused by phase transitions (D03 ↔ A2, D03 → L12, L12 ↔ D019, D019 ↔ B2, Fe13Ga9 → L12+Fe6Ga5 phases), and their influence on the above-mentioned thermally activated effects. We also report amplitude-dependent damping caused by dislocations and magnetic domain walls and try to understand the paradox between the Smith-Birchak model predicting higher damping capacity for materials with higher saturation magnetostriction and existing experimental results. The main attention in this review is paid to alloys with 17-20 and 25-30%Ga as the alloys with the best functional (magnetostriction) properties. Nevertheless, we provide information on a broader range of alloys from 6 to 45%Ga. Due to the limited space, we do not discuss other mechanical and physical properties in depth but focus on anelasticity. A short introduction to the theory of anelasticity precedes the main part of this review of anelastic effects in Fe-Ga and related alloys and unsolved issues are collected in summary.

Highly efficient capture of mercury from complex water matrices by AlZn alloy reduction–amalgamation and in situ layered double hydroxide

ABSTRACT Mercury pollution is a critical, worldwide problem and the efficient, cost-effective removal of mercury from complex, contaminated water matrices in a wide pH range from strongly acidic to alkaline has been a challenge. Here, AlZn and AlFe alloys are investigated and a new process of synergistic reduction–amalgamation and in situ layered double hydroxide (SRA-iLDH) for highly efficient capture of aqueous Hg(II) is developed using AlZn alloys. The parameters include the pH values of 1–12, the Hg(II) concentrations of 10–1000 mg L−1, and the alloy’s Zn concentrations of 20%, 50% and 70% and Fe concentrations of 10%, 20% and 50%. The initial rate of Hg(II) uptake by AlZn alloys decreases with increasing Zn concentration while the overall rate is not affected. Specifically, AlZn50 alloy removes >99.5% Hg(II) from 10 mg L−1 solutions at pH 1–12 in 5 min at a rate constant of 0.055 g mg−1 min−1 and achieves a capacity of 5000 mg g−1, being the highest value reported so far. The super-performance of AlZn alloy is attributed to multiple functions of chemical reduction, dual amalgamation, in situ LDH’s surface complexation and adsorption, isomorphous substitution and intercalation. This study provides a simple and highly efficient approach for removing Hg(II) from complex water matrices.

B2-structured Fe3Al alloy manufactured by laser powder bed fusion: Processing, microstructure and mechanical performance

Prealloyed Fe3Al was successfully manufactured by laser powder bed fusion. The best set of process parameters led to parts with a relative density of 99.5 %, a surface roughness, Sa, of 31.5 ± 5.6 μm and a hardness of 319 ± 14 HV0.1. Its microstructure as well as its mechanical properties at room and high temperatures were analyzed. The results of the chemical composition showed minor variations in aluminum content oscillating between 21 and 28 at.% along the melt pool. Additionally, elongated grains were observed to grow parallel to the building direction, as well as the development of a weak {001} texture along the building direction. The mechanical properties were influenced by the temperature. Compression tests showed a loss in strength with the increase in temperature, from a yield strength of 621 ± 40 MPa at room temperature to 89 ± 20 MPa at 650 °C. Reciprocating sliding wear tests showed that fragmentation of the intermetallic at room temperature occurs, whereas plastic deformation dominated at higher temperatures. For all temperatures, tribochemical wear was also present due to the oxidation of wear debris.

Why do Fe–Al Alloys Show Good Passivation Behavior in Acids Compared to Elemental Al?

We present some general concepts and pose questions connected to the difference between the ambient temperature passive film formed on elemental aluminum in acid vs that which forms on iron-aluminum alloys containing less than about 35–40 at% Al. Data is presented which demonstrates that the non-protective oxide that forms on aluminum is not related to impurity effects, either in the matrix or in grain boundaries.We argue that the ability of aluminum to form a protective passive film in a single-phase solid solution alloy is connected to atomic-scale size effects that vanish once the aluminum concentration increases to about 60 at%.

Effects of Mn and Cu Additions on Solidification Microstructure and High-Temperature Strength of Cast Al–Fe Binary Alloy

In order to investigate the effects of Mn and Cu additions on solidification microstructure and high-temperature strength of cast Al–Fe alloys, we have fabricated various Al–Fe-based alloys with compositions of Al–1%Fe, Al–1%Fe–1%Mn, Al–1%Fe–1%Cu, and Al–1%Fe–1%Cu–1%Mn (mol%) solidified at different cooling rates (0.3 K·s−1 and 145 K·s−1). In the Al–1%Fe binary alloy, the coarsened θ-Al13Fe4 phase with a needle-shaped morphology was often observed in the furnace-cooled sample (0.3 K·s−1), whereas the cast sample (145 K·s−1) exhibited several elongated α phases surrounded by fine α/Al6Fe eutectic microstructure. Such a solidification microstructure was observed in the cast Al–1%Fe–1%Cu alloy, whereas the Al23CuFe4 phase was locally formed in the finally solidified zone in the furnace-cooled sample. In the Al–1%Fe–1%Mn alloy, the Al6(Fe, Mn) phase was formed regardless of the cooling rate. Finer α/Al6(Fe, Mn) two-phase eutectic microstructure was almost entirely occupied in the cast sample. The fine eutectic microstructure was observed in the cast Al–1%Fe–1%Cu–1%Mn alloy as well. Compression tests for cast alloy specimens revealed that the Al–1%Fe–1%Cu–1%Mn alloy exhibited the highest strength level among the studied alloy specimens, indicating the combined addition of Mn and Cu elements could be effective in improving the high-temperature strength of the cast Al–Fe alloys.

4D forming shape memory component of Cu–13Al–5Fe alloy based on laser powder bed fusion of metal powders

High transition-temperature shape memory alloy (SMA) is widely used in aviation, aerospace and weapon fields. Using commercially available Cu, Al and Fe powders, Cu–13Al–5Fe alloy with high austenite transition temperature of 356–419 °C has been fabricated by laser powder bed fusion (LPBF) and a criterion for formulating the process parameters of LPBF based on the mixture of metal powders has been established. It is found that the LPBF can refine the structure, enhance the mechanical property and shape memory effect (SME). The structure of LPBF formed Cu–13Al–5Fe alloy under the quenched state is composed of tiny β′ martensite distributing in the matrix while the shape memory recovery rate can reach to 100% at the bending sample with 100°, and the shape memory recovery strain can reach to 1.08% under the 5% pre-strain by compressive test. Besides, the compressive stress and strain are 1240 MPa and 15.65% at room temperature. Compared with the arc-melted Cu–13Al–5Fe alloy under the quenched state, its shape memory recovery strain and recovery ratio are increased by 54.2% and 65%, respectively; and its compressive stress and strain are increased by 37.32% and 70.11%, respectively. Considering that, the work provides a criterion and a method for forming the component of Cu–Al–Fe alloy by LPBF based on the mixture of metal powders.