Primary crystallization in the Al-Fe-Mn-Ni-Si system as applied to casting alloys based on aluminum-nickel eutectic

Liquidus projections in characteristic sections of the Al-Fe-Mn-Ni-Si system in a range of up to 9% Ni, to 3% Fe, to 2% Mn, and 3% Si (wt %) are computed. The element concentrations at which the primary crystallization of the Al₃Ni, Al₉FeNi, Al₃Fe, Al₆(Fe, Mn), and Al₁₅(Fe,Mn)₃Si₂ intermetallide phases are determined. A good agreement between experimental and computed data is shown. When casting into metallic molds in the region of nickalin compositions, the formation of primary crystals of two Al₉FeNi and Al₆(Fe, Mn) phases is most probable. The primary crystallization of Al₃Ni and Al₁₅(Fe, Mn)₃Si₂ is possible only upon increased concentrations of nickel and silicon, and it takes slow solidification during casting in temporary molds to form the Al₃Fe phase.     

Investigation of the Effects of Ni, Fe, and Mn on the Formation of Complex Intermetallic Compounds in Al-Si-Cu-Mg-Ni Alloys

The aim of this work is to partially substitute Fe and Mn for Ni in the 3HA piston alloy and to study the consequences through microstructural evaluation and the thermal analysis technique. Three types of near-eutectic alloys containing (2.6 wt pct Ni-0.2 wt pct Fe-0.1 wt pct Mn), (1.8 wt pct Ni-0.75 wt pct Fe-0.3 wt pct Mn), and (1 wt pct Ni-1.15 wt pct Fe-0.6 wt pct Mn) were produced, and their solidification was studied at the cooling rate of 0.9 K/s (°C/s) using the computer-aided thermal analysis technique. Optical microscopy and scanning electron microscopy were used to study the microstructure of the samples, and energy dispersive X-ray (EDX) analysis was used to identify the composition of the phases. Also, the quantity of the phases was measured using the image analysis technique. The results show that Ni mainly participates as Al₃Ni, Al₉FeNi, and Al₃CuNi phases in the high Ni-containing alloy (2.6 wt pct Ni). In addition, substitution of Ni by Fe and Mn makes Al₉FeNi the only Ni-rich phase, and Al₁₂(Fe,Mn)₃Si₂ appears as an important Fe-rich intermetallic compound in the alloys with the higher Fe and Mn contents.     

Influence of iron and silicon on the phase composition and structure of heat-resistant casting nikalines strengthened by nanoparticles

The phase composition of the Al-Ni-Mn-Fe-Si-Zr system is analyzed as applied to heat-resistant nikalines (aluminum alloys of a new generation based on Ni-containing eutectic), which are strengthened by the Al₃Zr (L1₂) nanoparticles. It is shown that the presence of iron and silicon considerably complicates the phase analysis when compared with the AN4Mts2 base alloy. Silicon strongly widens the crystallization range, which increases the tendency of the alloy to form hot cracks during casting. It is shown that economically doped nikaline AN2ZhMts substantially exceeds the most heat-resistant cast aluminum alloys of the AM5 grade in the totality of its main characteristics (heat resistance and mechanical and production properties).     

On the nature of the Fe-bearing particles influencing hard anodizing behavior of AA 7075 extrusion products

The deleterious effects of Fe-bearing constituent particles on the fracture toughness of wrought Al alloys have been known. Recent studies have shown that the presence of Fe-bearing constituent particles is also detrimental to the nature and growth of the hard anodic oxide coating formed on such materials. The present study, using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron probe microanalysis (EPMA), was made to examine the influence of the nature of the Fe-bearing particles on the hard anodizing behavior of AA 7075 extrusion products containing varying amounts of Si, Mn, and Fe impurities. It was found that, in the alloy containing 0.25 wt pct Si, 0.27 wt pct Mn, and 0.25 wt pct Fe, the Fe-bearing constituent particles are based on the Al₁₂(FeMn)₃Si phase (bcc with a=1.260 nm). These particles survive the hard anodizing treatment, add resistance to the electrical path, causing a rapid rise in the bath voltage with time, and cause a nonuniform growth of the anodic oxide film. In the materials containing 0.05 wt pct Si, 0.04 wt pct Mn, and 0.18 wt pct Fe, on the other hand, the formation of the Al₁₂(FeMn)₃Si-based phase is suppressed, and two different Fe-bearing phases, based on Al-Fe-Cu-Mn (simple cubic with a=1.265 nm) and Al₇Cu₂Fe, respectively, form. Neither the Al-Fe-Cu-Mn-based phase nor the Al₇Cu₂Fe-based phase survive the hard anodizing treatment, and this results in a steady rise in the bath voltage with time and a relatively uniform growth of the anodic oxide film. Consideration of the size of the Fe-bearing particles reveals that the smaller the particle, the more uniform the growth of the anodic oxide film.     

On the nature of the Fe-bearing particles influencing hard anodizing behavior of AA 7075 extrusion products

The deleterious effects of Fe-bearing constituent particles on the fracture toughness of wrought A1 alloys have been known. Recent studies have shown that the presence of Fe-bearing, constituent particles is also determental to the nature and growth of the hard anodic oxide coating formed on such materials. The present study, using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron probe microanalysis (EPMA), was made to examine the influence of the nature of the Fe-bearing particles on the hard anodizing behavior of AA 7075 extrusion products containing varying amounts of Si, Mn, and Fe impurities. It was found that, in the alloy containing 0.25 wt pct Si, 0.27 wt pct Mn, and 0.25 wt pct Fe, the Fe-bearing constituent particles are based on the Al₁₂(FeMn)₃Si phase (bcc with α=1.260 nm). These particles survive the hard anodizing treatment, add resistance to the electrical path, causing a rapid rise in the bath voltage with time, and cause a nonuniform growth of the anodic oxide film. In the materials containing 0.05 wt pct Si, 0.04 wt pct Mn, and 0.18 wt pct Fe, on the other hand, the formation of the Al₁₂(FeMn)₃Si-based phase is suppressed, and two different Fe-bearing phases, based on Al−Fe−Cu−Mn-based (simple cubic with a=1.265 nm) and Al₇Cu₂Fe, respectively form. Neither the Al−Fe−Cu−Mn-based phase nor the Al₇Cu₂Fe-based phase survive the hard anodizing treatment, and this results in a steady rise in the bath voltage with time and a relatively uniform growth of the anodic oxide film. Consideration of the size of the Fe-bearing, particles reveals that the smaller the particle, the more uniform the growth of the anodic oxide film.     

An analytical electron microscopy study of constituent particles in commercial 7075-T6 and 2024-T3 alloys

To better understand the role of constituent particles in pitting corrosion, analytical electron microscopic studies were performed on the constituent particles in commercial 7075-T6 and 2024-T3 alloys. Five phases, namely, Al₂₃CuFe₄ and amorphous SiO₂ in 7075-T6 and Al₂CuMg, Al₂Cu, and (Fe,Mn) _x Si(Al,Cu) _y in 2024-T3, were identified. The crystal structure and chemistry of the Al₂₃CuFe₄, Al₂CuMg, and Al₂Cu phases in these alloys are in good agreement with the published data. Small deviations from their stoichiometric compositions were observed and are attributed to the influence of alloy composition on the phase chemistry. For the (Fe,Mn) _x Si(Al,Cu) _y (approximately, x=3 and y=11) phase, a rhombohedral structure, with lattice parameter a=b=c=1.598 nm and α=β=γ=75 deg, was identified and is believed to be a modified form of either Al₈Fe₂Si or Al₁₀Mn₃Si. Information from this study provided technical support for studying the electrochemical interactions between the individual particles (or phases) and the matrix. The corrosion results are reported in a companion article.     

Effect of Wavelike Sloping Plate Rheocasting on Microstructures of Hypereutectic Al-18?pct Si-5?pct Fe Alloys

To refine and spheroidize the microstructures of hypereutectic Al-Si-Fe alloys, a novel method of wavelike sloping plate (WSP) rheocasting was proposed, and the effect of the WSP rheocasting on the microstructures of hypereutectic Al-18 pct Si-5 pct Fe alloys was investigated. The results reveal that the morphologies of the primary Si crystal, the Al₁₈Si₁₀Fe₅, and the Al₈Si₂Fe phases can be improved by the WSP rheocasting, and various phases tend to be refined and spheroidized with the decrease of the casting temperature. The alloy ingots with excellent microstructures can be obtained when the casting temperature is between 943 K and 953 K (670 °C and 680 °C). During the WSP rheocasting, the crystal nucleus multiplication, inhibited grain growth, and dendrite break-up take place simultaneously, which leads to grain refinement of the alloys.     

Semisolid processing characteristics of AM series Mg alloys by rheo-diecasting

An investigation has been made into the solidification behavior and microstructural evolution of AM50, AM70, and AM90 alloys during rheo-diecasting, their processibility, and the resulting mechanical properties. It was found that solidification of AM series alloys under intensive melt shearing in the unique twin-screw slurry maker during rheo-diecasting gave rise to numerous spheroidal primary magnesium (Mg) particles that were uniformly present in the microstructure. As a result, the network of the β-Mg₁₇Al₁₂ phase was consistently interrupted by these spheroidal and ductile particles. Such a microstructure reduced the obstacle of deformation and the harmfulness of the β-Mg₁₇Al₁₂ network on ductility, and therefore improved the ductility of rheo-diecast AM alloys. It was shown that, even with 9 wt pct Al, the elongation of rheo-diecast AM90 still achieved (9 ± 1.2) pct. Rheodiecasting thus provides an attractive processing route for upgrading the alloy specification of AM series alloys by increasing the aluminum (Al) content while ensuring ductility. Assessment of the processibility of AM series alloys for semisolid processing showed that high Al content AM series alloys are more suitable for rheo-diecasting than low Al content alloys, because of the lower sensitivity of solid fraction to temperature, the lower liquidus temperature, and the smaller interval between the semisolid processing temperature and the complete solidification temperature.     

Microstructure and ordering of L12 titanium trialuminides

The present article reports and discusses the results of the microstructural characterization of various modifications of Ll₂ trialuminides containing various titanium contents, including the first ever report on their degree of ordering. The Ll₂ trialuminide alloys Al₃Ti + X, where X = Cu, Fe, Cr, and Mn were studied. The as-cast structure contains a very low level of porosity, and the amount of second phase depends on the particular alloy. After homogenization, the second phase is reduced in almost all the alloys to the level less than 0.5 pct, except for the Mn-high Ti alloy in which it remains at about 20 pct and its composition is 67.9 ± 0.6 at. pct Al, 2.2 ± 0.6 at. pct Mn, and 29.9 ± 0.3 at. pct Ti. In almost all the alloys, porosity after homogenization increases about twofold, except in the Al₃Ti + Cr alloy in which it remains at almost the as-cast level. Limited transmission electron microscopic observations have revealed the existence of very fine (≈10 nm) unidentified precipitates in the homogenized Al₃Ti + Cu alloy. The homogenized Al₃Ti + Cr and Mn alloys have greater lattice parameters than the Al₃Ti + Fe and Cu alloys. It is also found that the long-range order parameterS of the ho- mogenized Ll₂ Al₃Ti + X alloys dramatically decreases with increasing titanium content.     

Use of Calcium in Alloys: From Modifying to Alloying

Calcium is one of the most widespread and, consequently, low-cost metals on Earth. It has been applied for a long time in modifying and alloying alloys of heavy metals, in particular, lead and copper. It is used as a modifier in cast irons and steels. Calcium began being applied for alloying light alloys based on aluminum and magnesium comparatively recently. In this review, the application fields of metallic calcium and its influence on the structure and properties of various alloys are considered. Alloys based on aluminum–calcium eutectic have been systematically investigated over last few years, and it has been established that they possess casting properties no worse than these of silumins, and they can be hot-rolled and cold-rolled with a high degree of deformation. Ternary and more complex phase diagrams of systems including calcium are constructed and multicomponent alloys based on them are investigated. All these circumstances make it possible to outline several groups of new promising Ca-containing aluminum alloys: (i) alloys hardening without quenching due to the isolation of nanodimensional particles of Al₃Zr, Al₃Sc, and Al₃(Zr,Sc) phases; (ii) high-strength alloys alloyed with traditional hardening elements of the aluminum solid solution, such as zinc and magnesium; and (iii) composite alloys having more than 20% eutectic intermetallic compounds in the structure. All these materials have reduced density, an improved set of operational properties, increased corrosion resistance, and high manufacturability when producing cast and deformed half-finished products.     

Effects of Melt Thermal-Rate Treatment on Fe-Containing Phases in Hypereutectic Al-Si Alloy

In this paper, effects of melt thermal-rate treatment (MTRT) on Fe-containing phases in hypereutectic Al-Si alloy were investigated. Results show that MTRT can refine microstructures and improve castability, mechanical properties, wear characteristics, and corrosion resistance of Fe-containing Al-Si alloy. When Al-15Si-2.7Fe alloy is treated with MTRT by 1203 K (930 °C) melt: coarse primary Si and plate-like Fe-containing phase both can be refined to small blocky morphology, and the long needle-like Fe-containing phase disappears almost entirely; ultimate tensile strength and elongation are 195 MPa and 1.8 pct, and increase by 12.7 and 50 pct, respectively; and the wear loss and coefficient of friction decrease 7 to 17 and 24 to 30 pct, respectively, compared with that obtained with conventional casting technique. Corrosion resistance of the alloy treated with MTRT by 1203 K (930 °C) melt is the best, that is it has the lowest i _corr value and the highest E _corr value. Besides, effects of MTRT on Al-15Si-xFe (x = 0.2, 0.7, 1.7, 3.7, 4.7) alloys were also studied, MTRT can only refine microstructure and improve mechanical properties of Al-15Si alloy with 0.7 to 3.7 pct Fe content greatly in the present work.     

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.     

Phase formation in electrodeposited and thermally annealed Al-Mn alloys

Aluminum-manganese alloys with compositions ranging from 0 to 50 wt pct Mn were electrodeposited onto copper substrates from a chloroaluminate molten salt electrolyte containing MnCl₂ at temperatures of 150 °C to 325 °C. The structures of these electrodeposits were then compared to those observed when metastable electrodeposits were thermally annealed at 200 °C to 610 °C. The alloys were characterized by scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive spectroscopy, and X-ray diffraction. At deposition temperatures of 150 °C to 250 °C, no stable structure other than the strongly supersaturated and highly dislocated Al-face-centered cubic (fcc) solid solution is observed. An amorphous phase and body-centered cubic (bcc) Al₈Mn₅ are observed at higher manganese compositions. In the temperature range of 250 °C to 325 °C, some of the phases predicted by the equilibrium phase diagram, such as Al₆Mn and Al₁₁Mn₄, are electrodeposited. The direct deposition of the icosahedral and decagonal phases has been demonstrated at 325 °C. Thermal annealing of the amorphous phase at temperatures higher than 225 °C results in its transformation to the icosahedral phase with a grain size much smaller than that obtained in the electrodeposited icosahedral phase. Additional annealing at higher temperatures does not result in any detectable coarsening of the icosahedral phase; instead, crystals of Al₆Mn or Al₁₁Mn₄ grow into the regions once occupied by the icosahedral phase. The crystalline Al₆Mn phase which forms as the result of thermal annealing shows a structural deviation from the equilibrium phase. As-deposited alloys comprised of 2-to 3-nm-thick amorphous regions separated by fcc-Al grains failed to crystallize after 30 minutes annealing at 500 °C.     

Structure and properties of a rapidly solidified Al-Li-Mn-Zr Alloy for high-temperature applications: Part I. inert gas atomization processing

A new Al-Li alloy containing 2.3 wt pct Li, 6.5 wt pct Mn, and 0.65 wt pet Zr, for high-temperature applications, has been processed by a rapid solidification (RS) technique (as powders by inert gas atomization) and then thermomechanically treated by hot isostatic pressing (hipping) and hot extrusion. As-received and thermomechanically treated powders (of various size fractions) were characterized by X-ray diffraction and scanning and transmission electron microscopy (SEM and TEM, respectively). Phase analyses in the as-processed materials revealed the presence of two Mn phases (Al₄Mn and Al₆Mn), one Zr phase (Al₃Zr), two Li phases (the stable AlLi and the metastable Al₃Li), and the αAl solid solution with high excess in Mn solubility (up to close the nominal composition in the as-atomized powders). Extruded pieces were solutionized at 370 °C and 530 °C for various soaking times (2 to 24 hours). A variety of aging treatments was practiced to check for the optimal (for tensile properties) aging procedure, which was found to be the following: solutioning at 370 °C for 2 hours and water quenching + 1 pct mechanical stretching + one step aging at 120 °C for 3 hours. The mechanical properties, at room and elevated temperatures, of the “hipped” and hot extruded powders are compared following the optimal solutioning and aging treatments. The results indicate that Mn is indeed a favorable alloying element for rapidly solidified Al-Li alloys to retain about 85 to 95 pct of the room-temperature tensile properties even at 250 °C, though room-temperature strength is not satisfactory in itself. However, specific moduli are by 20 to 25 pet higher than those of the 2024 series duralumin-type alloys. Ductilities at room temperatures are in the low 1 to 2.5 pct range and show no improvement over other Al-Li alloys.     

Influence of the nonequilibrium crystallization on the phase composition of the Al-Mo-Ti alloy

The phase composition, microstructure, and crystal structure of the AMT TU-48-4-366 (Technical Specifications) foundry alloy (which is used as the alloying material when smelting titanium alloys) are investigated by X-ray phase analysis, electron probe microanalysis, and microscopy. Lattice parameters of ?, p, and δ phases are calculated and their elemental composition is revealed. No formation of the Mo₃Al refractory phase (t _m = 2150°C) is observed during the primary crystallization of the Al-Mo-Ti foundry alloy in nonequilibrium conditions. Its presence in the refractory phase in the foundry alloy is caused by secondary crystallization processes, during which an ultradispersed mixture of Mo₃Al + Mo₃Al₈ + TiMoAl₆ phases is formed at temperatures 1311 and 1314°C. The ultradispersed silicon-containing σ phase with the Mo_2.4Ti_2.1Si_0.8Al_4.7 average composition, which was formed in nonequilibrium crystallization conditions, is revealed. Parameters and interplanar distances of its lattice are determined. It is established that the largest nonuniformity by molybdenum in peritectics of primary crystals occurs at a high crystallization rate, i.e., in the lower part of the Al-Mo-Ti ingot.     

Microstructure Related Hydrogen Storage Capacity of Cast Mischmetal-Nickel Alloys Substituted with Aluminium,Manganese and Tin

Abstract

The morphology and compositions of the phases present in the microstructure of cast hydrogen storage MmNi_5-xAl_x (x= 0.4 and 0.8) MmNi_4.6 Sno₄ Mn, alloys (Mm = Indian Mischmetal) have been studied. Al, Mn and Sn substitutions for Ni in MmNis produce two-phase microstructures. The hydrogen storage capacity of these alloys is related with the volume fraction of the matrix phase. Higher the matrix volume fraction, higher the hydrogen storage capacity. The hydride forming elements that constitute Mm are present in greater proportion in the major constituent matrix phase of the two-phase structure. Only trace amounts of these elements are found in the precipitate phase in the Al- and Mn substituted alloys. However, for the Sn-substituted composition, the proportion of these elements is nearly same in matrix and precipitate phase.