Reoxidation of Aluminum in Fe-Al-M (M = C,Mn, and Ti) melts with CaO-Al2 O3-Fe t O (3 mass pct) slags

An Fe-0.01 to 0.5 mass pctAl alloy and an Fe-0.003 to 0.71 mass pctAl-1 mass pctM (M = C, Mn, and Ti) alloy were reoxidized with the CaO-Al₂O₃-Fe_tO (3 mass pct) slags at 1873 K in an Al2O3 or CaO crucible for 5 and 60 minutes. The contents of acid-insoluble Al, total O, and alloying element M in metal as well as those of M and FetO in slag were measured as a function of total Al content. On the basis of the present and previous results for Fe-Al-Te alloys, the effect of alloying elements on the degree of supersaturation with respect to the Al2O3 precipitation was studied. As a result, the supersaturation phenomenon was observed in all experiments at 5 minutes, but in the experiments at 60 minutes, it was observed only in Fe-Al and Fe-Al-Ti alloys. No supersaturation was observed in the reoxidation of Si in Fe-0.13 to 0.98 mass pctSi alloys with the CaO-SiO2-FetO (3 mass pct) slags in a CaO crucible at 5 and 60 minutes.     

Intermetallic-reinforced light-metal matrix in-situ composites

Transition-metal trialuminide intermetallics such as Al₃Zr and Al₃Ti, having low densities and high elastic moduli, are good candidates for the in-situ reinforcement of light-metal matrices based on Al and Mg alloys. In this work, in-situ composites based on Al and Al-Mg matrices reinforced with an Al₃Zr intermetallic were successfully processed by conventional ingot metallurgy. The microstructural studies showed that “needle” or “feathery”-like particles of Al₃Zr phase, whose volume fraction increased with increasing concentration of Zr, were formed in the Al matrix in the investigated range of Zr contents from 0.9 to 11.6 at. pct. Properties of Al-Zr alloys were investigated as a function of volume fraction of Al₃Zr. It is shown that the density, hardness, and yield strength of the in-situ Al/Al₃Zr composites can be quite adequately described by the composite rule-of-mixtures (ROM) behavior. Alloying of a binary Al-2.4 at. pct Zr alloy with Mg up to ∼25 at. pct reduces profoundly its density and, additionally, strengthens the matrix by a Mg solid-solution strengthening mechanism.     

Alloying mechanism of beta stabilizers in a TiAl alloy

The effects of beta stabilizers such as Fe, Cr, V, and Nb on the microstructures and phase constituents of Ti₅₂Al₄₈-xM (x=0, 1.0, 2.0, 4.0, or 6.0 at. pct and M=Fe, Cr, V, and Nb) alloys were studied. The dependence of the tensile properties and creep resistance of TiAl on the alloying elements, especially the formation of B2 phase, was investigated. Fe is the strongest B2 stabilizer, Cr is second, V is an intermediate stabilizer, and Nb is the weakest stabilizer. The composition partitioning of Fe, Cr, V, and Nb in the γ phase is affected by the formation of B2 phase. The peaks of the tensile strengths and creep rupture life of Ti₅₂Al₄₈-xM generally occur at the maximum solid solution of these elements in the γ phase, which is just before the formation of B2 phase. Ti₅₂Al₄₈-0.5Fe shows an attractive elongation of 2.5 pct at room temperature, and the Ti₅₂Al₄₈-1V, Ti₅₂Al₄₈-Cr, and Ti₅₂Al₄₈-2Nb alloys have about 1.1 to 1.3 pct elongation at room temperature. The increase of tensile strengths and creep resistance with increasing Fe, Cr, V, and Nb contents is chiefly attributed to the solid-solution strengthening of these elements in the γ phase. The appearance of B2 phase deteriorates the creep resistance, room-temperature strengths, and ductility. With respect to the maximum solid-solution strengthening, an empirical equation of the Cr equivalent [Cr] is suggested as follows: [Cr]=Cr+Mn+3/5V+3/8Nb+3/2 (W+Mo)+3Fe=1.5 to 3.0. The solid-solution strengthening mechanism of Fe, Cr, V, and Nb at room temperature arises from the increase of the Ti 3s and Al 2s binding energies in Ti-Ti and Al-Al bonds, and the retention of the strength and creep resistance at elevated temperatures in Ti₅₂Al₄₈-xM is mainly attributed to the increase of the Ti 3s and Al 2s binding energies in Ti-Al bonds in γ phase. The decrease of the Ti 3p and Al 2p binding energies in Ti-Ti, Ti-Al, and Al-Al bonds benefits the ductility of TiAl.     

Effect of alloying elements on martensitic transformation in the binary NiAl(β) phase alloys

The characteristics of the B2(β) to L1₀(β′) martensitic transformation in NiAl base alloys containing a small amount of third elements have been investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). It is found that in addition to the normal Ll₀ (3R) martensite, the 7R martensite is also present in the ternary alloys containing Ti, Mo, Ag, Ta, or Zr. While the addition of third elements X (X: Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Ta, W, and Si) to the binary Ni₆₄Al₃₆ alloy stabilizes the parentβ phase, thereby lowering the M_s temperature, addition of third elements such as Co, Cu, or Ag destabilizes theβ phase, increasing the M_s temperature. The occurrence of the 7R martensite structure is attributed to solid solution hardening arising from the difference in atomic size between Ni and Al and the third elements added. The variation in M_s temperature with third element additions is primarily ascribed to the difference in lattice stabilities of the bcc and fcc phases of the alloying elements.     

Deoxidation equilibria of calcium and magnesium in liquid iron

Calcium-oxygen and magnesium-oxygen equilibria in liquid iron saturated with CaO-SiO₂-Al₂O₃-MgO slags were studied at 1873 K using CaO, Al₂O₃, and MgO crucibles. The applicability of the first-order and second-order interaction coefficients between Ca and O and between Mg and O was studied by comparing the Ca-O and Mg-O equilibria observed in the present and previous experiments with the calculated ones from the respective interaction coefficients. As a result, the interaction coefficients obtained in the present work by using a new method were found to explain the measured solubilities of CaO and MgO. The phase stability region in Fe-Al-M (M=Ca, Mg)-O system was described at 1873 K.     

The effect of composition and milling conditions on the structure of mechanically alloyed Mg-Al based alloys

Mg-Al based alloys were mechanically alloyed under varying conditions. Elemental reaction times correlated with known diffusion coefficients and elemental hardness, but milling temperature had almost no effect over a 200 °C range. Increasing impact energy caused the steady-state level of crystallinity to increase. Alloys with up to 6 at. pct of Ti, Y, Ca, Zr, V, Er, or Pr yielded amorphous alloys near the composition Mg₄₀Al₆₀. Certain phases were suppressed by mechanical alloying, while others became more dominant than in the equilibrium phase diagram. These effects are explained by differential scanning calorimetry (DSC) results, which indicate they are growth rate controlled during mechanical alloying. Hard elements such as Cr and Mo with positive free energy of mixing did not react completely even after relatively long milling times.     

Texture Modification During Extrusion of Some Mg Alloys

The effects of extrusion ratio and alloying addition on the microstructure of Mg-0.2 wt pct Ce alloys are investigated by electron backscatter diffraction. The results show that in this alloy, texture randomization does not occur at high or low extrusion ratios but at a ratio of 25:1 at 400 °C. When extruded at the same temperature and extrusion ratio, Ca addition to Mg results in a weak nonbasal texture. In contrast, Mg-Al and Mg-3 wt pct Al-0.2 wt pct Ce alloys do not exhibit texture modification in single-pass extrusion. In the Mg-Al-Ce alloy, Ce and Al form Al₁₁Ce₃ particles, leaving little Ce solute in the matrix. The texture modifications in Mg-Ce or Mg-Ca alloys are related to the nature of the solid solution and consistent with dynamic strain aging during extrusion.     

Alloy design and coarsening phenomenon of L12 precipitates in high-temperature Al-2 At. Pct (Ti,V,Zr) systems

Aging works of two melt-spun Al-2 at pct (Ti,V,Zr) alloys showed that metastable L1₂ Al₃(Ti,V,Zr) precipitates were dominant and did not transform to stable D0₂₃ ones: the average radius was 3 to 4 nm and the interparticle spacing was 10 to 30 nm at 698 K up to 400 hours. Coarsening kinetics was found to be very sluggish and was coincident with the low lattice mismatch. Due to the low coarsening rate and the high thermal stability of the precipitated phase, rapidly so-lidified Al-Ti-V-Zr systems show promise as base of high-strength Al alloys for high-temperature applications. Formerly with the Department of Materials Science andEngineering, Korea Advanced Institute of Science and Technology, Taejon, Korea     

A study on the microstructural evolution of Al-25 at. pct V-12.5 at. pct M (M = Cu,Ni, Mn) powders by planetary ball milling

The alloying behavior of Al-25 at. pct V-12.5 at. pct M (M = Cu, Ni, Mn) by planetary ball milling of elemental powders hours as been investigated in this study. In Al₃V binary system, an amorphous phase was produced after 6 hours and the amorphous phase was mechanically crystallized after 20 hours. The large difference in the diffusivities between Al and V atoms in Al matrix results in the formation of the amorphous phase when the homogeneous distribution of all the elements in a powder was achieved at 6 hours. According to thermal analyses, the amorphous phase in the binary Al₃V was crystallized at 350 °C. The addition of ternary elements (Cu, Ni, Mn) increased the activation energy for the crystallization to D0₂₂ phase by interfering with the diffusion process. Therefore, ternary element addition improved the thermal stability of the amorphous structures. The amorphous phase in the 12.5 at. pct Ni added Al₃V was crystallized to D0₂₂ phase at 540 °C. The mechanical crystallization of the amorphous phase in the ternary element-added Al-V system either occurred later or was not observed during ball milling up to 100 hours. It is thought that the amorphous intermetallic compacts could be produced more easily in ternary element-added alloys by using an advanced consolidation method.     

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.     

Evolution of microstructures in the nickel modified titanium trialuminides near the L12 phase field

This study focuses upon the evolution of microstructures during solidification processing of several intermetallic alloys around the Ll₂ phase in the Al-rich corner of the Al-Ti-Ni ternary system. The alloys were produced by double induction melting and subsequent homogenization followed by furnace cooling. The microstructure was characterized by means of optical and scanning electron microscopy with energy-dispersive spectroscopy (EDS) analysis and X-ray diffraction. The microstructural evolution in homogenized alloys was dependent on both nickel and titanium content. Very fine precipitates of Al₂Ti were observed within the Ll₂ phase in alloys containing 62 to 65 at. pct Al and at least 25 at. pct Ti. The Al₂Ti precipitates are stable at least up to 1000 °C and undergo complete dissolution at 1200 °C. In alloys containing around 66 at. pct Al and 25 to 31 at. pct Ti, phases such as Al₃Ti, Al₅Ti₂, and Al₁₁Ti₅ were observed. A modified room temperature isotherm in the Al-Ti-Ni ternary system is proposed, taking into account the existence of Al₂Ti, Al₁₁Ti₅, Al₅Ti₂, and Al₃Ti in equilibrium with the Ll₂ phase. It seems that at room temperature, the Ll₂ phase field for homogenized alloys is extremely small. It will be practically impossible to obtain a single-phase microstructure at room temperature in the Al-Ti-Ni ternary alloys after homogenization at 1000 °C followed by furnace cooling. S. BISWAS, formerly Graduate Student, Department of Mechanical Engineering, University of Waterloo     

Microstructure and Mechanical Properties of Extruded Magnesium-Aluminum-Cerium Alloy Tubes

Current commercial magnesium extrusion alloys do not offer desirable combinations of strength, ductility, and extrusion speed for automotive structural applications. The effect of small additions of cerium (Ce) to pure magnesium (Mg) and Mg-3 pct Al alloy extruded tubes has been studied. The results suggest that 0.2 pct Ce addition can significantly improve the extrudability and mechanical properties of the Mg extrusions. The improvement in mechanical properties is due to grain refinement and dispersion strengthening provided by the Mg₁₂Ce particles and the beneficial texture obtained. Higher Ce contents further increase strength, but significantly reduce ductility and cause excessive surface oxidation during extrusion. The beneficial effect of 0.2 pct Ce on mechanical properties of pure Mg is not observed when it is added to Mg-3 pct Al alloy, due to the higher affinity of Ce to Al to form the Al₁₁Ce₃ phase in the Mg-Al-Ce ternary alloys. The Mg-0.2 pct Ce alloy is a promising base alloy for further development in automotive applications; however, Al should be avoided in Mg-Ce–based extrusion alloys.     

Quantitative evaluation of inclusion in deoxidation of Fe-10 mass pct Ni alloy with Si, Ti, Al, Zr, and Ce

The composition, size, number, and morphology of the inclusions in deoxidation of Fe-10 mass pct Ni alloys with 0.2 mass pct M (M=Si, Ti, Al, Zr, and Ce) containing mostly 60 to 130 mass ppm oxygen were studied as a function of holding time at 1873 K. It was found that the initial primary inclusions contained FeO and the FeO content decreased with an increase of deoxidation power and holding time. The mean spatial diameter of inclusions tends to increase with increasing holding time, but did not show the systematic trend with respect to the deoxidation power. The number of particle sections per unit area decreased with decreasing deoxidation power and increasing holding time. In the absence of stirring of melt, the growth rate of the mean spatial diameter of inclusions and the removal rate of particle sections per unit area decreased rapidly with increasing holding time and approached a constant after 10 minutes. The morphology of inclusions was found to be spherical, polyhedral (except Si), and irregular including cluster, and the mean spatial diameter of these inclusions increased with increasing holding time.     

Thermodynamic effect of alloying addition on <Emphasis Type="Italic">in-situ</Emphasis> reinforced TiB<Subscript>2</Subscript>/Al composites

From the viewpoint of thermodynamics, using the Wilson equation and an extended Miedema model, the effect of the alloying element on the stability of the precipitated phases during the fabrication of in-situ reinforced TiB₂/Al composites was evaluated. The result shows that additions of alloying elements, such as Mg, Cu, Zr, Ni, Fe, V, and La, can promote the formation of Al₃Ti and TiB₂ phases. Particularly, Zr has the most pronounced effect among these alloying elements. In addition, alloying elements can hinder the formation of AlB₂ to a small extent. The calculation results also show that it is easier for magnesium to react with the salts to form TiB₂ than aluminum during the fabrication of in-situ reinforced TiB₂/Al using the flux-assisted synthesis (FAS) technology.     

The effect of metallic elements on the crystallization behavior of amorphous Fe-Si-B alloys

The crystallization behavior of amorphous Fe_84-X Si₆B₁₀M_X (M=Nb, Zr, V, or Cu) alloys was examined using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) with the aim of clarifying the effect of additional M elements. The compositional dependence of the first crystallization temperatureT _x1 increased in the order of Zr > Nb > V; however, the addition of 1 at. pct Cu caused a decrease inT _x1. Such an effect of the M elements on the thermal stability of an amorphous phase was interpreted in terms of the difference in the atomic size. These alloys were composed of a mixed structure ofα-Fe and amorphous phases after aging for 3.6 ks in the first exothermic temperature range. The addition of more than 3 at. pct Nb or Zr significantly affected the morphology and grain size of theα-Fe phase. However, their particles possessed dendritic morphology with a grain size of 0.1 to 0.3 μm, when the Nb or Zr content was less than 2 at. pct. Further addition of these elements brought about the formation of sphericalα-Fe particles. The average grain size, for instance, was as small as 20 nm in the aged alloy containing 6 at. pct Nb, which shows that a remarkable grain refinement occurs with increasing Nb content.     

Strength Improvement Through Grain Refinement of Intermetallic Compound at Al/Fe Dissimilar Joint Interface by the Addition of Alloying Elements

Dissimilar material joining between Al alloys and steel may be effective in decreasing the weight of automobile bodies. In this study, dissimilar lap joining of Al alloys containing certain alloying elements, such as Ni, Cr, Mn, Ti, or Si, to interstitial-free steel was performed by tungsten inert gas arc brazing, and the effect of the alloying element on the joint strength associated with the Al-Fe intermetallic compound layer at the dissimilar interface was examined. The addition of an appropriate amount of an alloying element to the alloy increased the joint strength; the addition of Ni exhibited the most effective improvement. The additions of some elements changed the grain structure of the η-Fe₂Al₅ layer but not its chemical composition. This is the first study to clarify that smaller grain size of η-Fe₂Al₅ correlated to greater strength of the Al/Fe dissimilar joint.     

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.     

Understanding the Co-Poisoning Effect of Zr and Ti on the Grain Refinement of Cast Aluminum Alloys

The “co-poisoning” effect between Zr and Ti (derived from Al-Zr and Al-Ti-B master alloy additions) on the grain refinement of cast aluminum alloys is studied from a crystallographic atom matching viewpoint. The edge-to-edge matching (E2EM) model has been used to investigate the possible “poisoning” phase containing Zr/Ti, Al, and Fe in commercial grade aluminum alloys. The results show that Al₃Ti is the most likely constituent to be poisoned due to the formation of an Al₈Fe₄Zr coating on its surface, since the Al₈Fe₄Zr phase has good crystallographic atom matching with Al₃Ti, but not with the aluminum matrix. Meanwhile, the partial dissolution of Al₃Zr nucleant particles to compensate for the loss of solute Zr aggravates the poisoning phenomenon. This proposed mechanism is consistent with most previous experimental observations and with existing practical solutions employed in the foundry.