On the stable Mg-Zn-Y quasicrystals

By the conventional air-cooled casting method, bulk ingots with a large fraction of stable Mg-Zn-Y icosahedral quasicrystals, both simple and face-centered, were obtained. The quasicrystal structures were directly confirmed by high-resolution electron microscopy (HREM) observations. The electron diffraction patterns from the quasicrystals were studied by computer simulations. A coexisting crys-talline phase of the quasicrystals was identified as the Mg₇Zn₃ phase, which was proved to be the (1/1) approximant of the quasicrystals. The quasicrystals were stable during a continuous heating process. However, at high temperature, oxidation occurred, and thus, Y₂O₃ and MgO products were formed. Oxidation at high temperatures is characteristic for the Mg-Zn-Y alloys and differs from Al-base alloys.     

Effect of Ca and Rare Earth Additions on the Texture,Microhardness, Microstructure and Structural Properties of As-Cast Mg–4Al–2Sn Alloys

In this work, alloys with nominal composition of Mg–4Al–2Sn–xRE–yCa (where RE = rare earth, x = 0, 1, 3 and y = 0, 1) have been prepared using tilt casting method. Prepared as-cast samples have been investigated by X-ray diffractometry, optical microscopy and scanning electron microscopy techniques as well as hardness measurement. The texture, microstructure and structural parameters of samples were also refined from X-ray diffraction patterns utilizing the Rietveld method and generalized spherical-harmonic model. It was found that with addition of rare earth and calcium elements, intermetallic phases of γ-Mg₁₇Al₁₂ and β-Mg₂Al₃ disappeared in cast alloys while small amount of Al₁₁RE₃ and CaMgSn intermetallics phases are formed. The texture factor of α-Mg as a main phase of samples was decreased with addition of rare earth up to 1 % and increased with more addition of rare earth elements. According to the results, with addition of rare earth elements, texture of Mg phase changes from 〈112〉 direction to 〈100〉 and 〈002〉 directions while Ca addition causes the texture in 〈002〉 direction. The microhardness of Mg–4Al–2Sn alloy was enhanced with addition of rare earth and calcium elements which is in agreement with the expected trend based on computed phase fraction of the samples. Addition of 1 wt% of calcium causes a dramatic change in the morphology and chemical composition of intermetallic phases, from acicular shape with composition of Al₁₁RE₃ into fine feather of CaMgSn intermetallic phase which accumulated in cluster morphologies in interdendritic regions.     

Recycling of magnesium alloys: Chemical equilibria between magnesium-lithium-based melts and salt melts

Magnesium-lithium alloys have been equilibrated with chloride melts at 700 °C in iron crucibles. After quenching, the compositions of the metal and salt phases were determined by chemical analyses. The obtained data were evaluated according to thermodynamic principles. The following reactions were investigated: MgCl₂+2Li=2LiCl+Mg (Reaction [1]), CaCl₂+2Li=2LiCl+Ca (Reaction [2]), and BaCl₂+2Li=2LiCl+Ba (Reaction [3]). The equilibrium of Reaction [1] is much on the right side of the reaction equation. If calcium chloride or barium chloride are added to the salt mixture (to increase the density), these chlorides are partially reduced, leading to pickup of calcium or barium, respectively, by the metal phase. Reaction [1] can be utilized in two different recycling schemes. With a magnesium chloride free lithium chloride-potassium chloride mixture, remelting of magnesium-lithium alloys is possible without loss of lithium to the slag. On the other hand, the lithium can be separated from the magnesium by conversion to lithium chloride using a magnesium chloride rich slag.     

Effect of Zn Content on Microstructure and Mechanical Properties of MgZnYLaMM Alloys

The effect of Zn content on microstructure, existing phases, and mechanical properties of rapidly solidified MgZn _x Y₁LaMM₁Mn_0.5 alloys (X?=?2, 3, 4 at.?pct) has been investigated. To assess the microstructural characterization of nanocrystalline alloys, the study also includes microstructural characterization of the master alloys. The microstructure of the alloys in as-rapidly solidified condition consisted of supersaturated magnesium dendrites and fine (Mg,Zn)₁₇La₂ and W phase (Mg₃Y₂Zn₃) segregated at grain and cell boundaries. During continuous heating, the metastable solid solution in Mg dendrites breaks down, increasing the volume fraction of second-phase particles. After annealing for 1?hour at 673?K (400?°C), very small spherical Mn-rich precipitates appeared in the three alloys and a long-period stacking ordered (LPS) phase of rectangular morphology precipitated inside the Mg grains in the alloy with the lowest Zn content. The nanocrystalline nature of the ribbons accounts for the high hardness and yield stress values in as-rapidly solidified state, although both decrease with increasing zinc content. This fact has been related to a coarser microstructure and higher volume fraction of the W phase as the Zn content increases. The highest yield stress value of 350?MPa is attained by the MgZn₂Y₁LaMM₁ ribbon in as-rapidly solidified condition. A decrease in yield stress values (about 50?MPa) is observed for all ribbons when they are heated at 673?K (400?°C) for 1?hour.     

Phase equilibria in the binary rare-earth alloys: The erbium-magnesium system

The Er-Mg system was examined using differential thermal analysis (DTA), X-ray examination, metallography, and microprobe analysis. Four intermediate phases are found to exist, and their crystal structures have been confirmed or determined as the following:β phase (≈Er₂Mg) (cubic, cI2-W type, peritectic formation 1255 °C); ErMg (cubic, cP2-CsCl type, peritectic formation 830 °C); ErMg₂ (hexagonal, hP12-MgZn₂ type, peritectic formation 670 °C); and Er₅Mg₂₄ (cubic, cI58-α-Mn type, peritectic formation 600 °C). Theβ phase undergoes a eutectoidal decomposition at 680 °C and 30.5 at. pct Mg. A eutectic reaction was observed to occur at 570 °C and 89.5 at. pct Mg. Comparisons of the general properties between the ErMg phases and with those of the other R-Mg compounds (R = rare earth) are briefly discussed. Properties and structures of the R-Mg, R-rich alloys are specially considered and compared with those of a few groups of rare-earth alloys. The alloying behavior of R-rich R-Me alloys (R = Ho, Er, Tm, Lu; Me = Mg, Cd, In, Tl) is systematically presented and/or predicted.     

Metallurgical reactions in two industrially strip-cast aluminum-manganese alloys

Precipitation, phase transformation, subgrain growth, and recrystallization that occur during heat treatment of two strip-cast, cold-rolled, high manganese aluminum alloys have been studied mainly by transmission electron microscopy (TEM). The alloys differ in silicon content. The isothermal heat treatments have been performed in a salt bath at temperatures between 330 °C and 530 °C for times up to 1000 hours. Size distributions for each type of secondary particle have been determined. After short annealing times, small quasicrystals precipitated and subsequently transformed to α phase. The densities of these precipitates controlled dislocation movement and regulated subgrain sizes. Prolonged heating resulted in peritectoid reactions to Al₆Mn or Al₁₂Mn. Recrystallization, which is associated with the formation of Al₁₂Mn, is advanced by increasing the silicon content; the nucleation and growth of Al₁₂Mn occurs only at the expense of other phases that stabilize the subgrain network. Formerly with SINTEF, Oslo, Norway     

Crystallization kinetics of amorphous magnesium-rich magnesium-copper and magnesium-nickel alloys

Amorphous magnesium-rich alloys Mg _y X_1-y (X=Ni or Cu and 0.82<y<0.89) have been produced by melt spinning. The crystallization kinetics of these alloys have been determined by in situ X-ray diffraction (XRD) and isothermal and isochronal differential scanning calorimetry (DSC) combined with ex situ XRD. Microstructure analysis has been performed by means of transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Crystallization of the Mg-Cu alloys at high temperature takes place in two steps: primary crystallization of Mg, followed by simultaneous crystallization of the remaining amorphous phase to Mg and Mg₂Cu. Crystallization of the Mg-Cu alloys at low temperatures takes place in one step: eutectic crystallization of Mg and Mg₂Cu. Crystallization of the Mg-Ni alloys for a Mg content, y>0.85, takes place in two steps: primary crystallization of Mg and of a metastable phase (Mg_∼5.5Ni, with Mg content y=0.85), followed by the decomposition of Mg_∼5.5Ni. Crystallization of the Mg-Ni alloys for a Mg content y<0.85 predominantly takes place in one step: eutectic crystallization of Mg and Mg₂Ni. Within the experimental window applied (i.e., 356 K<T<520 K and 0.82<y<0.89), composition dependence of the crystallization sequence in the Mg-Cu alloys and temperature dependence of the crystallization sequence in the Mg-Ni alloys has not been observed.     

Al–Cu–Li and Al–Mg–Li alloys: Phase composition,texture, and anisotropy of mechanical properties (Review)

The results of studying the phase transformations, the texture formation, and the anisotropy of the mechanical properties in Al–Cu–Li and Al–Mg–Li alloys are generalized. A technique and equations are developed to calculate the amounts of the S₁ (Al₂MgLi), T₁ (Al₂CuLi), and δ' (Al₃Li) phases. The fraction of the δ' phase in Al–Cu–Li alloys is shown to be significantly higher than in Al–Mg–Li alloys. Therefore, the role of the T₁ phase in the hardening of Al–Cu–Li alloys is thought to be overestimated, especially in alloys with more than 1.5% Li. A new model is proposed to describe the hardening of Al–Cu–Li alloys upon aging, and the results obtained with this model agree well with the experimental data. A texture, which is analogous to that in aluminum alloys, is shown to form in sheets semiproducts made of Al–Cu–Li and Al–Mg–Li alloys. The more pronounced anisotropy of the properties of lithium-containing aluminum alloys is caused by a significant fraction of the ordered coherent δ' phase, the deformation mechanism in which differs radically from that in the solid solution.     

Formation of Quasicrystals and Related Structures in Systems of Aluminum with Transition Metals. Part 2. Binary Systems Formed by Aluminum with 4d and 5d Metals

Numerous systems for aluminum with transition metals have been found to contain quasiperiodic phases (quasicrystals) having symmetries forbidden by classical crystallography. These phases are metastable in binary systems and have been obtained by rapid cooling from the liquid or gaseous phases. Binary quasicrystals are considered along with revised phase diagrams for the systems Al – 4d-M and Al – 5d-M (M from Mo to Pd and from W to Pt).     

Effect of copper and magnesium on the structure and the phase composition of boron/aluminum composite ingots

The phase composition of aluminum Al–B–Cu–Mg alloys has been studied using calculations and experimental methods. Unlike copper, magnesium is shown to substitute aluminum in the AlB₂ phase substantially. The use of Al–Cu–Mg alloys (duraluminums) as the matrix of boron/aluminum composite prepared by liquid-phase technologies is substantiated.     

Phase structure and electrochemical properties of laser sintered La2MgNi9 hydrogen storage electrode alloys

Phase structure and electrochemical properties of laser sintered La2MgNi9 alloys were studied. The sintered alloys contained a main phase, LaNi5, and a ternary La-Mg-Ni phase, with a PuNi3 structure and a small amount of LaMgNi4. The ternary La-Mg-Ni phase with a PuNi3 structure had the composition of La1.8Mg1.2Ni9 and La2MgNi9, for alloys laser sintered at 1000 and 1400 W, respectively. Owing to further reactions between LaNi5 and LaMgNi4, the amount of the PuNi3 phase increased for alloys sintered at 1400 W. Both alloys had good activation property (three charge/discharge cycles). The discharge capacities of the sintered alloys were 321.8 and 344.8 mAh/g, respectively. Compared with the alloy laser sintered at 1000 W, the poor cyclic stability of the alloy sintered at 1400 W was mainly attributed to the lower corrosion resistance of the La2MgNi9 phase.     

Electrodeposition of Mg-Li-Al-La Alloys on Inert Cathode in Molten LiCl-KCl Eutectic Salt

Electrochemical preparation of Mg-Li-Al-La alloys on inert electrodes was investigated in LiCl-KCl melt at 853 K (580 °C). Cyclic voltammograms (CVs) and square wave voltammograms (SWVs) show that the existence of AlCl₃ or AlF₃ could promote La deposition on an active Al substrate, which is predeposited on inert electrodes. All electrochemical tests show that the reduction of La³⁺ is a one-step reduction process with three electrons exchanged. The reduction of La(III)→La(0) occurred at –2.04 V, and the underpotential deposition (UPD) of La was detected at –1.55 V (vs Ag/AgCl). The same phenomena concerning La UPD were observed on two inert cathodes, W and Mo. In addition, Mg-Li-Al-La alloys were obtained by galvanostatic electrolysis on the W cathode from La₂O₃ in LiCl-KCl-MgCl₂-KF melts with aluminum as the anode. X-ray diffraction (XRD) measurements indicated that various phases like the Al₂La, Al₁₂Mg₁₇, and βLi phase (LiMg/Li₃Mg₇) existed in the Mg-Li-Al-La alloys. The distribution of Mg, Al, and La in Mg–Li–Al-La alloys from the analysis of a scan electron micrograph (SEM) and energy dispersive spectrometry (EDS) indicated that the elements Mg, Al, and La distributed homogeneously in the alloys.     

Phase relationships in the neodymium-magnesium alloy system

The Nd-Mg system was studied using differential thermal analysis (DTA), X-ray examination, metallography, and microprobe analysis. The following intermetallic compounds were found to exist and their crystal structures confirmed or determined: NdMg (cubic, cP2 CsCl type, melting point 800 °C), NdMg₂ (cubic, cF24 MgCu₂ type, peritectic formation ∼755 °C), NdMg₃ (cubic, cF16 BiF₃ type, melting point 780 °C), and Nd₅Mg₄₁ (tetragonal, tI92 Ce₅Mg₄₁ type, decomposes peritectically at 560 °C). The NdMg₂ phase undergoes a eutectoidal decomposition at 660 °C. Three eutectic equilibria were observed to occur at 42.5 at. pct Mg and 775 °C, 64.5 at. pct Mg and 750 °C, and 92.5 at. pct Mg and 545 °C, respectively. In the Nd-rich alloys, previously determined data^[15] concerning the Mg solubility in α-Nd (8.2 at. pct Mg, ≈550 °C) were accepted. The Mg solubility in β-Nd was evaluated as 34 at. pct Mg at 775 °C. The β-Nd phase was observed to decompose eutectoidally at 17 at. pct Mg and 545 °C. Moreover, in the Mgrich alloys, a metastable NdMg₁₂ phase (tetragonal, tI26 ThMn₁₂ type) was observed in samples quenched from the liquid. The general properties of the Nd-Mg phases are compared with those of the R-Mg compounds and briefly discussed.     

Effect of ferrosilicon addition on the composition of inclusions in 16Cr-14Ni-Si stainless steel melts

The silicon deoxidation equilibrium between the 16Cr-14Ni-1.5Mn-Si melts and the CaO-SiO₂-8MgO-5CaF₂ (basicity=1.8) slag at 1743 K was investigated to understand the effect of aluminum and silicon contents on the composition of inclusions. Therefore, the ferrosilicon alloys with different aluminum content were chosen based on the preceding objective. In addition, the phase stability diagram of the inclusions was computed using commercial thermodynamic software based on the Gibbs energy minimization principles. The content of MnO in the inclusions sharply decreases with increasing silicon content when the steel melts were deoxidized by the ferrosilicon alloys containing high aluminum (FeSi-H). The content of SiO₂ in the inclusions slightly increases with increasing silicon content when the FeSi-L is used, while a maximum value is shown at [Si]=1.5 pct when the FeSi-H is used. The content of MgO in the inclusions increases by increasing the content of silicon, regardless of the kinds of ferrosilicon alloys. The use of the FeSi-L as a deoxidizer could suppress the formation of Al₂O₃ in the inclusions, while the content of Al₂O₃ increases with increasing silicon content when the FeSi-H is used. When the FeSi-H is used as a deoxidizer, the inclusions are the glassy type with the composition of Mn-silicates at [Si]≤1.3 pct, while the Mg(Ca)-silicates with the composition of the forsterite phase are observed in the steel composition of [Si]=3.3 pct. When the steel melts were deoxidized by the FeSi-L alloys, the inclusions are the glassy-type Mn-silicates at [Si]=0.8 pct, while the Mn-silicates containing the cristobalite phase are observed at [Si]=1.5 to 2.4 pct. In the composition of [Si]=3.3 pct, the Mg-silicates with the composition of the rhodonite phase are observed. The log(X _SiO2/X _MnO) of the inclusions linearly increases by increasing the log [a _Si · a _O / a _Mn] with the slope close to unity when the FeSi-L is used as a deoxidizer, while the slope of the line is about 2 times greater than that of the expected value when FeSi-H is used. The log (X _MgO/X _MnO) of the inclusions linearly increases by increasing the log [a _Mg/a _Mn] with slopes greater than the expected value of unity.     

Modulated structures and GP Zones in Al-Mg Alloys

The formation of modulated structures and GP zones in Al-Mg alloys aged at low temperatures was investigated using the mechanical properties, electrical resistivity measurements, and high resolution electron microscopy. It was shown in TEM investigations that a modulated structure was present in Al-10 wt pct Mg alloys at the beginning of low temperature aging which grew into GP zones having the Ll₂ structure distributed periodically along the [100] direction. The miscibility gaps for GP zone formation and the spinodal temperature were determined from the results of resistivity measurements. It is suggested that in Al-Mg alloys spinodal decomposition can occur at the beginning of low temperature aging. Y. KOJIMA, formerly with Tokyo Institute of Technology     

Effects of Be and Fe additions on the microstructure and mechanical properties of A357.0 alloys

A357 hypoeutectic alloy is a heat-treatable Al-Si-Mg system with a nominal composition of Al-7 pct Si and about 0.6 pct Mg have widespreaded applications, especially in the aerospace and automotive industries. The purpose of this study was to determine the influences of Be and Fe content on the microstructure and mechanical properties of A357.0 alloys. Distinct morphologies were discerned between Be-containing and Be-free alloys. The Be-free alloys contain larger amount of iron-bearing phases with Mg than in Be-containing alloys. The addition of Be can change the plateletlike structure of iron-bearing phases to a comparatively harmless round nodular form. Also, the amounts of iron-rich phases are significantly lower and the silicon particles are smaller and more spherical in the Be-containing alloys. Small amounts of Be in A357.0 caused significant increases in the precipitation kinetics of Mg₂Si. It was found that the addition of Be lowers the ternary and binary eutectic melting point. The amount of Mg available to form the major strengthening phase Mg₂Si is increased promoting the tensile strength of A357.0 casting. The tensile properties were improved with decreasing Fe content and the addition of Be. The effect is more apparent in the higher Fe alloys than that in the lower Fe alloys.     

Influence of magnesium on electrochemical properties of RE3-xMgx(Ni0.7Co0.2Mn0.1)9（x=0.5-1.25） alloy electrodes

RE3-xMgx(Ni0.7Co0.2Mn0.1)9 (x=0.5-1.25) alloys were prepared by induction melting and the influence of the partial substitution of RE (where RE stands for La-rich mischmetal) by Mg on the hydrogen storage and electrochemical properties of the alloys were investigated systematically. These alloys mainly consisted of three phases, La(Ni,Mn,Co)5 phase, La2Ni7 phase and Mg2Ni phase. The P-C-T isotherms showed that with Mg content increasing in the alloys, the hydrogen storage capacity first increased and reached the maximum capacity of 1.36 wt.% when x=1.0, and then decreased with x increasing further. Electrochemical studies revealed that the discharge capacity reached the maximum value of 380 mAh/g and the alloy electrode presented better cyclic stability when RE/Mg=2. The high rate discharge ability of the alloy electrodes was also improved by the substitution of Mg for RE. The RE2Mg(Ni0.7Co0.2Mn0.1)9 alloy exhibited better hydrogen absorption kinetics (x=1.0).)     

Tensile Flow Behavior of Tungsten Heavy Alloys Produced by CIPing and Gelcasting Routes

Present work describes the flow behavior of tungsten heavy alloys with nominal compositions 90W-7Ni-3Fe, 93W-4.9Ni-2.1Fe, and 95W-3.5Ni-1.5Fe (wt pct) produced by CIPing and gelcasting routes. The overall microstructural features of gelcasting are finer than those of CIPing alloys. Both the grain size of W and corresponding contiguity values increase with increase in W content in the present alloys. The volume fraction of matrix phase decreases with increase in W content in both the alloys. The lattice parameter values of the matrix phase also increase with increase in W content. The yield strength (σ_YS) continuously increases with increase in W content in both the alloys. The σ_YS values of CIPing alloys are marginally higher than those of gelcasting at constant W. The ultimate tensile strength (σ_UTS) and elongation values are maximum at intermediate W content. Present alloys exhibit two slopes in true stress–true plastic strain curves in low and high strain regimes and follow a characteristic Ludwigson relation. The two slopes are associated with two deformation mechanisms that are occurring during tensile deformation. The overall nature of differential curves of all the alloys is different and these curves contain three distinctive stages of work hardening (I, II, and III). This suggests varying deformation mechanisms during tensile testing due to different volume fractions of constituent phases. The slip is the predominant deformation mechanism of the present alloys during tensile testing.     

Phase composition,texture, and anisotropy of the properties of Al–Cu–Li–Mg alloy sheets

The formation of the anisotropy of the mechanical properties, the texture, and the phase composition of thin-sheet Al–4.3Cu–1.4Li–0.4Mg and Al–1.8Li–1.8Cu–0.9 Mg alloys have been studied by X-ray diffraction and tensile tests. Various types of anisotropy of the strength properties of the alloys have been revealed: normal anisotropy (strength in the longitudinal direction is higher than that in the transverse direction) in the Al–4.3Cu–1.4Li–0.4Mg alloy and inverse anisotropy in the Al–1.8Li–1.8Cu–0.9Mg alloy. It is shown that the anisotropy of the strength properties is dependent not only on the texture of a solid solution, but also on the content and the texture of the δ' (Al₃Li) and T1 (Al₂CuLi) phases and their coherency and compatibility of deformation with the matrix.