FeAl Phase Research Articles

Effects of Cold‐Rolling Reduction on Microstructure, Thickness, Surface Roughness of AS20/20 and on Bending Toughness of AS20/20‐Coated Press‐Hardened Steel

The tailor‐rolling blanks based on Al–Si‐coated press‐hardened steel (PHS) have attracted much attention along with the development of lightweight vehicles. The properties of Al–Si‐coated PHS with single surface weight of 20 g m−2 change after cold‐rolling and then austenitization, which are little studied. Herein, the effects of cold‐rolling reduction ratio on the microstructure, thickness, and roughness of AS20/20 coatings, and on the bending toughness of AS20/20‐coated PHS, are explored. The overall continuity of the coatings is unchanged as the reduction ratio increases. When the reduction ratio is 30% or above, rapid diffusion channels are formed at the cracks of Al‐filled intermetallic compound layer. Meanwhile, the thickness and surface roughness of the coatings are stable and do not decrease. After austenitization, the coatings are structurally consistent with the increase of the reduction ratio. When the reduction ratio is 30% and above, the thickness and surface roughness of the coatings are stable and do not decrease. The rapid diffusion channels lead to an increment in the proportion of FeAl phase to above 96% after austenitization, which makes the bending angle further increase. The bending angle is enlarged by 44% when the reduction ratio is 50%.

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.

Revealing the Epitaxial Interface between Al13Fe4 and Al5Fe2 Enabling Atomic Al Interdiffusion

Steel is the most commonly manufactured material in the world. Its performances can be improved by hot-dip coating with the low weight aluminum metal. The structure of the Al∥Fe interface, which is known to contain a buffer layer made of complex intermetallic compounds such as Al5Fe2 and Al13Fe4, is crucial for the properties. On the basis of surface X-ray diffraction, combined with theoretical calculations, we derive in this work a consistent model at the atomic scale for the complex Al13Fe4(010)∥Al5Fe2(001) interface. The epitaxial relationships are found to be [130]Al5Fe2∥[010]Al13Fe4 and [1 1̅0]Al5Fe2 ∥[100]Al13Fe4. Interfacial and constrained energies, as well as works of adhesion, calculated for several structural models based on density functional theory, identify the lattice mismatch and the interfacial chemical composition as main factors for the stability of the interface. Molecular dynamics simulations suggest a mechanism of Al diffusion to explain the formation of the complex Al13Fe4 and Al5Fe2 phases at the Al∥Fe interface.

3D-structure of intermetallic interface layer in Al–steel clad material

This paper reveals the 3D character of the intermetallic layer at the aluminum–steel interface which pops up above the original sample surface during annealing. Popping out of the intermetallics was proven using atomic force microscopy. The phase expands out of the plane due to the exothermic formation of the Al5Fe2 phase and the feasibility of surface diffusion. Milling by a focused ion beam enabled the comparison of the chemical composition of the surface layer with the bulk interface, showing no difference. The growth direction is both towards aluminum and steel — the main diffusion flux is from aluminum towards steel, and the new intermetallic phase emerges at the steel side. The shortage of Al atoms causes a shift of the intermetallic as a whole towards aluminum.

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.

Effect of rare-earth Sc on the interface microstructure and mechanical properties of Al/steel bimetallic composites prepared by liquid–solid casting

In this study, scanning electron microscopy (SEM), electron backscatter diffraction analysis (EBSD), and electron probe microanalysis (EPMA) were used to investigate the impact of rare-earth Sc on the interface microstructure and mechanical properties of Al/steel bimetallic composites fabricated by liquid–solid casting. With the addition of 0.3% Sc, the morphology of eutectic Si changed from needle-like to fibrous and granular. The addition of Sc did not change the types of intermetallic compounds in the Al/steel reaction layer, which comprised the Al5Fe2, τ1-Al2Fe3Si3, Al13Fe4, τ5-Al7Fe2Si, and τ6-Al9Fe2Si2 phases. The thickness of the first layer decreased, whereas that of the second layer increased as the Sc content increased to 0.3%. Furthermore, the Al5Fe2 and τ1 phase percentages of the reaction layer decreased, whereas the Al13Fe4, τ5, and τ6 phase percentages increased. Sc was mainly enriched in the front of the ternary compound layer (τ6) near the Al side. The addition of 0.3% Sc reduced the grain size of each phase in the interfacial reaction layer and did not change the preferred orientation of the Al5Fe2, Al13Fe4, τ5, and τ6 phases, but increased the polar density of the Al13Fe4, τ5, and τ6 phases and decreased the polar density of the Al5Fe2 phase. With the addition of 0.3% Sc, the average nanohardness of the reaction layer decreased by 5% and the bonding strength increased by 48%.

ABRASIVE WEAR RESISTANCE OF FE3AL AND STELLITE 6 COATINGS FOR THE PROTECTION OF VALVE SEATS SURFACES

The development of a technology that increases the service life of valve seats in CNG/LNG-powered vehicles requires the appropriate selection of material and the technology of its application. Commercially used valve seat materials show accelerated wear under operating conditions, especially in natural gas vehicle engines. The authors developed a new material concept and a new technological concept for the protection of the valve seat in CNG/LNG-powered vehicles. This article aims to present the first stage of tribological research. Two materials were used in the research: Stellite 6 alloy and Fe3Al intermetal. A commonly used material for valve seats of combustion engines is Stellite 6. The Fe3Al is the new proposed material coating for the protection of the valve seats of internal combustion engines. This article compares the abrasive wear resistance of these materials. The abrasion tests were performed on a T-11 pin-on-disc tester, and the counter-sample was steel S235JR. The test conditions were similar to those prevailing during the operation of the valves in the head of the internal combustion engine, without the influence of temperature. The obtained results indicate that the Fe3Al intermetal is characterized by a lower coefficient of friction and lower wear intensity than Stellite 6. The results confirm that the Fe3Al phase is a prospective material to be used as a protective material on the valve seat of vehicles.

Mechanism of Diffusion-Zone Formation at the Al–Fe Phase Interface under Impact-Loading Conditions

Mechanism of Diffusion-Zone Formation at the Al–Fe Phase Interface under Impact-Loading Conditions

Controlling interfacial composition and improvement in bonding strength of compound casted Al/steel bimetal via Cr interlayer

The fabrication of Al/steel bimetal with a good metallurgical interface is always a great challenge, particularly for the improvement of bonding strength due to the inevitably extensive formation of brittle Al–Fe intermetallic compounds (IMCs) at the interface. Therefore, in this work, the electroplated Cr coating with thickness of 5 μm was firstly used as the interlayer of Al/steel bimetal to suppress Al–Fe IMCs and further improve the interfacial bonding strength. Al/steel bimetal was prepared by compound casting combined with a hot-dip aluminizing process. The results showed that the interface of Al/steel bimetal with Cr interlayer contained an unmolten Cr coating and a reaction layer, in which the latter consisted mainly of Al13Cr4Si4, Al5Cr, Al-rich solid solution and CrSi2 phases. Besides, the morphology of these new Al–Cr–Si and Al–Cr phases was granular rather than the tongue-shaped of Al–Fe phase and the polygonal blocky of Al–Fe–Si phase. Both the microstructure characterization and kinetics calculation results revealed that the application of Cr interlayer could avoid the contact between Fe atoms from steel side and Al atoms from Al alloy side, thereby suppressing the formation of brittle Al–Fe phases at the interface. Moreover, the reaction layer showed a lower nano-hardness than that of without Cr interlayer. With assistance of Cr interlayer, Al/steel bimetal with maximum shear strength of 115.5 MPa was obtained and the interface failed through the Al alloy side. The morphology characteristic and lower nano-hardness of these new phases, the composite structure consisting of Al–Cr–Si and Al–Cr layer together with the Al-rich solid solution layer greatly contributed to the enhancement of the interfacial strength for the Al/steel bimetal.

On the localized corrosion of AA5083 in a simulated dynamic seawater/air interface—Part 1: Corrosion initiation mechanism

Localized corrosion of the aluminium alloy AA5083-H111 in a simulated dynamic seawater/air interfacial zone and a full seawater immersion zone was investigated with electrochemical impedance spectroscopy and electrochemical noise. Al-Fe/Ti intermetallic particles (IMPs) on localized corrosion were examined with focused ion beam, transmission electron microscopy and energy dispersive x-ray spectroscopy. As compared with the full immersion zone, the interfacial zone showed higher oxide film resistance and charge transfer resistance, which was attributed to the high oxygen flux in that zone. Localized corrosion arose from IMPs that posessed an Al-Fe phase and a Ti enriched phase.

In-situ synchrotron X-ray radiography study of primary Fe-rich phases growth in Al-Fe( Cu) alloys

Plate-like iron-rich intermetallic phases (Fe-rich phases) greatly decrease the elongation and fatigue strength of recycled Al alloys. The alloy composition and the manufacturing process parameters influence the type, and shape of Fe-rich phases. In this study, the influence of the cooling rate (0.1, 0.5, and 1.0 °C/s) on the nucleation and growth of primary Fe-rich phases during solidification of Al-Fe(Cu) alloy has been quantified by synchrotron X-ray radiography. The Kikuchi patterns and deep-etched methods showed that rod-shape and plate-like primary Al3Fe phases are present in the studied alloy. The in-situ experimental results indicate that the total number and number density of primary Fe-rich phases in AlFe alloys is very similar at cooling rates of 0.1 °C/s and 1.0 °C/s but increases a 300 % at cooling rate of 0.5 °C/s. The nucleation rate of Al3Fe in AlFe alloys at three cooling rates (0.1, 0.5, and 1.0 °C/s) are 15.5, 44.0, 25.0 No./s, respectively. These decrements are due to alloy compositions are very closed to the eutectic composition (about 1.8% Fe), the less time for them to form primary Fe-rich phases at high cooling rate of 1.0 °C/s. The variation trend of total number, number density, and nucleation rate of primary Al3Fe phases in Al-Cu-Fe alloys is similar to those of in AlFe alloys. The maximum length of typical Al3Fe phases in AlFe alloys decrease from 845 μm to 222 μm as the cooling rate increased. This is because that higher cooling rate resulting in less diffusion time for limiting Fe atoms diffusion, also inhibiting them grow into large plates. The combined Cu addition and higher cooling rate resulting in the constitutional undercooling, and finally promote the formation of refined primary Al3Fe particles.

Evaluation of microstructure and mechanical behavior of Aluminum 2024 and Stainless steel 304 GTAW joints

This study aims to evaluate the microstructure and mechanical behavior of aluminum 2024 and stainless steel 304 dissimilar joints. The gas tungsten arc welding (GTAW) process has been employed to weld base metals by inserting copper-nickel-based (Cu-10%Ni) filler metal. The effects of GTAW parameters such as welding current, welding speed, and gas flow on microstructure and tensile strength have been analyzed through the Taguchi method. Results revealed that tensile strength is primarily influenced by welding current, followed by speed and gas flow rate. The excellent joint strength of 138 MPa has been achieved by using Cu-10%Ni filler metal. The optimal combination of parameters, i.e., welding current of level 2 (80 A), welding speed of level 1 (100 mm/min), and gas flow rate of level 3 (10 l/min), has been obtained through SN ratio optimization. Microstructure and EDS analysis depicted that the weld zone of a high-strength joint contained fine dendrites and CuAl and NiAl solid solutions, while the weld zone of a low-strength joint featured coarse dendrites and brittle FeAl phases.

Mechanism of accelerating creep rupture under high stress level of pack cementation aluminide coatings deposited onto T92 steel tube

An aluminide coating was deposited on commercial T92 steel by pack cementation. The coating exhibits a typical bilayer structure composed of an outer FeAl layer and an inner interdiffusion layer. The creep rupture life of the coated and uncoated T92 was investigated. Results show that the rupture life of the coated T92 decreases significantly, i.e., decreases by 46 % at the creep stress of 110 MPa compared with the uncoated T92. By examining the microstructure and fractography of the coated specimen, the mechanism of aluminide coating deteriorating creep rupture life is clarified. The main fracture mode of T92 substrate with and without coating is microvoid accumulation fracture. The characteristic microstructure of the aluminide coating is responsible for the premature creep rupture. The formation of columnar grains and brittle nature of FeAl phase make it tend to crack during creep. The phase transformation and needle-like AlN precipitates in the inner interdiffusion layer contribute to the inward propagation of cracks and accumulation of creep damage.

STRUCTURE, MECHANICAL PROPERTIES, AND OXIDATION RESISTANCE OF MN-RICH FE-MN-AL ALLOYS

In this study, Mn-rich Fe-Mn-Al alloys with different Al content (Al = 0, 3, and 5 % by weight) were fabricated from ferromanganese lumps using a conventional powder metallurgy technique. The samples were compacted in 1 cm steel dies using a load of 8 tons and then sintered at 1100 °C for 2 h in a tubular furnace under a vacuum condition of around 0.5 mbar. To evaluate the effect of Al addition to Fe-Mn-Al alloy, the Archimedes principle and Vickers hardness were applied to estimate the density and hardness of the compact alloys. Moreover, the high-temperature oxidation resistance of the alloy was evaluated at 800 °C for 8 cycles. The structure of the alloy before and after oxidation was studied by means of X-Ray Diffractometer and SEM-EDS. The XRD analysis results show that the FeMn-0Al alloy is mainly composed Fe3Mn7 phase, the presence of FeAl phase at 3 wt% Al, and Al8Mn5 phase at 5 wt% Al. The density and hardness of Fe-Mn-Al alloys decreased with the increased Al content. Fe-Mn-Al alloy without Al addition exhibits poor oxidation resistance since the first cycle of the test. The results of microstructural analysis showed that although the alloy with the addition of 3 wt% Al showed less mass gain after being exposed for 8 cycles at 800 °C, the Fe-Mn-Al alloy with 5 wt% tended to be more resistant to oxidation and had no cracking defects. The structure of the oxide formed on the surface of the alloy is composed of two layers (ie; outer and inner layer) which are affected by each alloy composition.

Microstructure and mechanical properties of laser welded hot-press-formed steel with varying thicknesses of Al–Si coatings cleaned by nanosecond pulsed laser

The Al–Si coatings are commonly used for hot-press-forming (HPF) steel to prevent oxidation in the automobile industry. However, due to the presence of Al–Si coating, undesirable intermetallic compounds are easily formed in the welds of HPF steel. In this work, an environment-friendly and effective nanosecond pulsed laser cleaning process was used to remove the Al–Si coating, and HPF steel with varying thicknesses of coatings was prepared for laser welding. The microstructure and mechanical properties of laser welded HPF steel with different thicknesses of coatings were further investigated. The results showed that there was a threshold of power to remove the Al–Si coatings in the laser cleaning process. The reduced thickness of coatings not only could improve the stability of the welding process due to the diminishing of metal vapor generated by coating ablation, but also decrease the content of the Fe–Al phase in the welded joint, which is detrimental to weld performance. The tensile strength and cupping test pass rate of weld joints gradually increased with the decreasing thickness of coatings to 5 μm. After that, the Al–Si coating almost had no effect on the mechanical properties of the laser weld joints. The laser weld joint with 5 μm-thick of Al–Si coating showed, a tensile strength of 1435.05 MPa, a microhardness of 488.38 HV and a pass rate of 100% for the cupping test.

Study of Microstructure and Properties of Aluminum/Steel Inertia Radial Friction Welding

In this paper, 6061-T6 aluminum alloy and 30CrMnSiA steel are bonded by inertia radial friction welding (IRFW). The formation mechanism of the aluminum/steel friction welded joints and the effect of the welding parameters on the mechanical properties are investigated through the microstructure, microzone composition, and mechanical property analysis. The results show that no visible intermetallic compound layers (IMCs) are detected on the aluminum/steel welding interface, which may be due to Si element aggregating in the welding interface and then forming a Al−Fe−Si phase, preventing the formation and growth of an Al−Fe IMCs. Eventually, a micron ultrathin interface reaction layer composed of Al0.7Fe3Si0.3, FeAl, and Fe3Al phases is formed at the aluminum/steel welding interface. The maximum average shear strength of the joint is 176 MPa. The shear fracture is a typical ductile fracture. Properly reducing the friction speed and increasing the upsetting pressure can improve the bonding strength of aluminum/steel joints.

Synthesis of Ferroalloys via Mill Scale-Dross-Graphite Interaction: Implication for Industrial Wastes Upcycling

Mill scale and aluminum dross are the industrial wastes from steel and aluminum industries, which have high concentrations of Fe2O3 and Al2O3, respectively. This paper reports the conversion of reducible metal oxides in scale and dross into an alloy via carbothermic reduction at 1550 °C. Scale and dross were mixed with graphite into three different C/O molar ratios of 1, 1.5, and 2 to produce a pellet. The pellets were heated at 1550 °C for up to 6 h under an argon atmosphere. By this method, carbothermic reductions were found to proceed and formed Fe–Si–Al–C alloy that consists of Fe3Al and Fe3Si phases. The presence of Si in the alloy came from the reduction of SiO2 in aluminum dross. Levels of Al and Si in the alloy increase with increasing C/O molar ratios. However, the Si level in the alloy was found to stabilize since 3 h, while the Al level increases with increasing time up to 6 h. Unreacted oxides in the wastes had an insignificant effect on the ferroalloy formation. These results provide evidence for carbothermic reduction of the Fe2O3-Al2O3-SiO2 system at 1550 °C and show the novel method to upcycling aluminum dross and mill scale toward a circular economy.

Impurity iron separation from molten secondary aluminum by pulsed electric current

Secondary aluminum has received extensive attention due to its low energy consumption, low emissions, and good recyclability; however, the high impurity iron content in secondary aluminum limits its development. Traditional iron removal methods generally have the problems of high cost and low efficiency. Therefore, exploring an efficient, economical, and environmentally friendly iron removal method is of great significance for achieving sustainable development and adhering to a circular economy. The effect of pulsed electric current on the distribution of impurity element iron in secondary aluminum melt was investigated. Compared to the non-pulsed sample, iron impurity accumulates near the cathode and at the bottom in the pulsed sample, while the content in the middle region is greatly reduced, that is, the impurity iron in the secondary aluminum melt is effectively driven and separated. Based on the difference in the effective charge number between Al and Fe, the iron atoms are forced to diffuse and move directionally toward the cathode under the action of electromigration, resulting in a gradual increase in the concentration of iron atoms near the cathode. According to the Al-Fe phase diagram, the increase of iron content makes the solidification point of the alloy to the right, and the solidification temperature of the alloy increases. In other words, at the same temperature, the Fe-rich phase is preferentially precipitated near the cathode. Due to the different electrical conductivity from the matrix, the Fe-rich phase migrates to the bottom of the melt driven by electrical free energy.

Effect of Chloride and Iodide on the Corrosion Behavior of 13Cr Stainless Steel

The corrosion behavior and mechanism of 13Cr stainless steel in the solution with 1 mol/L NaCl and 5 mmol/L KI were investigated by weight loss method, scanning electrochemical microscopy (SECM), the phase analysis (XRD) of inclusions, and surface analysis technique (SEM and EDS). Results showed that the corrosion rate was a linear relationship with the time and Cl− concentration. The corrosion became serious with the increase in time and Cl− concentration. The corrosion occurred in the unstable electroactive points that contained aluminum oxide and metallic phase inclusions. The generation and disappearance of the electroactive points simultaneously occurred with the corrosion. The active dissolved level on different areas of the surface of 13Cr stainless-steel sample was different. The oxidation current peak of the sample presented the strip shape. The corrosion dissolution was mainly caused by aluminum oxide inclusions (Al2O3) and FeAl phase.

High strength and rapid solution Mg alloy by adding Fe element fabricated by binder jetting additive manufacturing

The effects of Fe addition on the mechanical properties and corrosion behaviors of AZ91D alloys prepared by binder jetting additive manufacturing have been investigated. The results show that the constitution of the second phase is large dependence on Fe content. With the Fe content increasing, the second phase can transform AlFe phase to Fe and AlFe phase. In addition, with increasing Fe content, the content of second phase increases gradually, while the content of pores also increases. We believe that with the Fe content increasing, the content of second phase with Fe element increases which the melt temperature is higher than sintering temperature, and the content of liquid phase decreases, that leading the high-viscosity liquid alloy cannot fill the pores fully and the more pores will remain and causes the relative density reduces. The compressive strength shows a parabola relationship with Fe content. Furthermore, adding Fe can accelerate the degradation of Mg alloys owing to the galvanic corrosion. The sample with 5 wt% Fe content shows the highest ultimate compressive strength (440 MPa) and fast degradation rate (9091 mm/Y), which meets the soluble Mg alloy with rare earth but cost much lower.