Solid Solution Of Magnesium Research Articles

Mechanical properties and wear characterization of Al-Mg composites synthesized at different temperatures

<abstract> <p>Reactive sintering of Al-Mg powder mixtures containing 5, 10, 15, and 20 wt.% Mg was used to synthesize lightweight composites reinforced with in-situ formed Al<sub>3</sub>Mg<sub>2</sub> and Al<sub>12</sub>Mg<sub>17</sub> intermetallics. Detailed microstructural investigation and phase analysis were employed to examine the phases in the composites formed at 400 and 450 ℃. The creation of particles with the Al<sub>12</sub>Mg<sub>17</sub> cores encapsulated by the Al<sub>3</sub>Mg<sub>2</sub> phase, which was further covered by a continuous aluminum matrix, was observed in the composites synthesized at 400 ℃. If the composites were held at 450 ℃, the liquid phase appeared at the Al-Mg interface, and as a result, a two-phase mixture was formed. It was the eutectic composed of the Al<sub>3</sub>Mg<sub>2</sub> intermetallic compound and a solid solution of magnesium in aluminum (Al). The introduction of magnesium particles into the aluminum matrix resulted in a decrease in the density of composites, but there was no significant difference in the density of composites sintered at different temperatures. The mechanical behavior of the composites was examined using microhardness and hardness measurements and a room-temperature compression test. The result of using different cooling speeds, with the furnace and quenching in water, was the refining of the grains in the Al<sub>3</sub>Mg<sub>2</sub> + (Al) eutectic, resulting in an increase in microhardness. The increase in hardness of the composites was related to the amount of particles introduced. Sintering at 450 ℃ and the cooling method influenced the hardness and compressive strength of the composites, which were higher by 10% and 13%, respectively, compared to composites sintered at 400 ℃. Tribological tests showed that introducing more and more magnesium particles into the aluminum matrix, followed by reactive sintering, increased the wear resistance. On the other hand, the sintering temperature and cooling conditions had little effect on the wear resistance of the Al-Mg composites.</p> </abstract>

Analysis of contact zone of coating-substrate system exposed to irradiation with a pulse electron beam

Using the wire-arc additive manufacturing method (WAAM) on a 5083 aluminum alloy substrate, a non-equiatomic Mn – Cr – Fe – Co – Ni high-entropy alloy (HEA) coating was formed. By scanning and transmission electron diffraction microscopy we analyzed the structure, phase and elemental composition of the contact zone after irradiation with high-current low-energy electron beams with the following parameters: accelerated electron energy 18 keV, electron beam energy density 30 J/cm2, electron beam pulse duration 200 µs, number of pulses 3, pulse repetition rate 0.3 s–1. Multiphase multielement submicro- and nanocrystalline structures are formed predominantly in the substrate, which has a lower melting temperature compared to HEAs. Mutual doping of the coating – substrate system occurs in the contact layer, which has sinuous boundaries. The contact layers adjacent to the substrate and coating have the structure of high-speed cellular crystallization. In the layer adjacent to the substrate, the cells are formed by a solid solution of magnesium in aluminum. Interlayers of the second phase, enriched in atoms of the coating and substrate, are revealed along the cell boundaries. In the layer adjacent to the coating, the cells are formed by an alloy of composition 0.17Mg – 20.3Al – 4.3Cr – 16.7Fe – 9.3Co – 49.2Ni corresponding to the coating. Interlayers of the second phase, enriched mainly in magnesium and, to a lesser extent, in atoms of the HEA coating, are located along the cell boundaries. Central region of the contact zone with a thickness of ~1700 μm is formed by lamellar crystallites, which indicates the eutectic nature of its formation. Its main element is aluminum (≈77 at. %).

Nanostructured strain-hardened aluminum-magnesium alloys modified by C60 fullerene obtained by powder metallurgy Part 2. The effect of magnesium concentration on physical and mechanical properties

This paper is intended to continue the studies of magnesium effects on the structural phase composition, physical and mechanical properties of the nanostructured strain-hardened aluminum-magnesium alloys modified with C60 fullerene [1]. Previously obtained mechanically alloyed composite powders [1] were consolidated by direct hot extrusion method. Consolidation parameters were chosen based on previous studies of the structure and phase composition formation during mechanical alloying and heat treatment. It was found that an increase in magnesium concentration improves mechanical properties of extruded nanosructured composite materials, and additives modified by C60 fullerene stabilize the grain structure and slow down decomposition of α solid solution of magnesium in aluminum to 300 °C. Under similar thermobaric treatment Al82Mg18 (AMg18) not modified with C60 demonstrates a reduced α solid solution lattice constant and an increased average crystallite size. These processes are accompanied by sequential formation of γ, β′, and β phases, while γ and β′ are intermediate phases. The grain structure of extruded samples is typical for materials obtained in this way – grains are closely packed, elongated and oriented along the extrusion axis. The grain structure of extruded samples inherits the morphology of mechanically alloyed powders. Thus, mechanical alloying methods followed by intense plastic deformation (extrusion) improved mechanical properties significantly. Materials with ultimate tensile strength of 880 MPa; ultimate bending strength of 1100 MPa; microhardness up to 3300 MPa; and with the same density of 2.4–2.6 g/cm3 were obtained. This result demonstrates the prospects for using powder metallurgy techniques in the production of new nanostructured composite materials modified by C60 fullerene with improved physical and mechanical properties.

Kinetics and Phase Transformations during the Decomposition of Supersaturated Solid Solutions of Magnesium in Mg–Dy–Sm Alloys

Kinetics and phase transformations are studied for the previously unconsidered decomposition of supersaturated solid solution in magnesium-based alloys Mg–Dy–Sm. The decomposition of solid solution slows when there is an increase in % Dy: % Sm ratio in the alloys. Mg–Sm and Mg–Dy alloys grow harder when Dy and Sm are added to them, respectively. Products of decomposition in ternary Mg–Dy–Sm alloys are the same as in binary alloys Mg–Dy and Mg–Sm but contain combinations of Dy and Sm.

EIS and corrosion behaviour of plasma sprayed layers of Al and AlCr6Fe2 on AZ91

Abstract This work presents the preparation of coatings of aluminium and AlCr6Fe2 alloy on magnesium alloy AZ91 with metallurgical bonding. Coatings were prepared by plasma spraying system WSP®-H 500. This metallurgical bond (sub-layer) is formed by an eutectic structure consisting of the intermetallic phase Mg17Al12 and the solid solution of magnesium and aluminium. In this work, the layers were studied using electrochemical impedance spectroscopy (EIS). It was shown that there is a several fold increase of the polarization resistance (Rcν) of plasma-sprayed coatings of aluminium and AlCr6Fe2 alloy, compared with uncoated AZ91 in borate buffer with pH 9.1.

Electron energy spectrum and the specific features of the optical absorption of solid solutions of magnesium, aluminum, and boron oxides

A calculation scheme based on density functional theory, generalized for the case of periodic structures, is used to calculate the electron energy spectrum of binary and ternary oxides of magnesium, aluminum, and boron with MgBxAl2−xO4 spinel structure. The dependences of the electron energy and geometric characteristics of the studied structures on the degree of substitution x are examined. It is shown that, by changing this parameter (i.e., the composition of the ternary oxide), it is possible to adjust the bandgap width and the position of the chemical potential for boron-magnesium-aluminum spinel. The dependence of the imaginary part of the relative permittivity on the energy of absorbed photons is obtained and analyzed.

Mg xMn (1−x)(BH 4) 2 ( x = 0–0.8), a cation solid solution in a bimetallic borohydride

A solid solution of magnesium and manganese borohydrides was studied by in situ synchrotron radiation X-ray powder diffraction and infrared spectroscopy. A combination of thermogravimetry, mass and infrared spectroscopy, and atomic emission spectroscopy were applied to clarify the thermal gas desorption of pure Mn(BH 4) 2 and a solid solution of composition Mg 0.5Mn 0.5(BH 4) 2. Mg x Mn (1− x )(BH 4) 2 ( x = 0–0.8) conserves the trigonal structure of Mn(BH 4) 2 at room temperature. Manganese is dissolved in the hexagonal structure of α-Mg(BH 4) 2, with the upper solubility limit not exceeding 10 mol.% at room temperature. There exists a two-phase region of trigonal and hexagonal borohydrides within the compositional range x = 0.8–0.9 at room temperature. Infrared spectra show splitting of various vibrational modes, indicating the presence of two cations in the trigonal Mg x Mn (1− x )(BH 4) 2 solid solutions, as well as the appearance of a second phase, hexagonal α-Mg(BH 4) 2, at higher magnesium contents. All vibrational frequencies are shifted to higher values with increasing magnesium content. The decomposition temperature of the trigonal Mg x Mn (1− x )(BH 4) 2 ( x = 0–0.8) does not vary significantly as a function of the magnesium content (433–453 K). The desorbed gas contains mostly hydrogen and 3–7.5 mol.% diborane B 2H 6, as determined from analyses of the Mn(BH 4) 2 and Mg 0.5Mn 0.5(BH 4) 2 samples. An eutectic relation between α-Mg(BH 4) 2 and LiBH 4 is observed. The solid solution Mg x Mn (1− x )(BH 4) 2 is a promising material for hydrogen storage as it decomposes at a similar temperature to Mn(BH 4) 2, i.e. at a much lower temperature than pure Mg(BH 4) 2 without significantly losing hydrogen weight capacity thanks to substitution of Mn by Mg up to 80 mol.%. The questions of diborane release and reversibility remain to be addressed.

Structure Refinement of the Multi-Phase Mg-Al-Sr Alloy

The AJ63 magnesium alloy contains 6 wt.% aluminum and 3 wt.% strontium. The typical microstructure of this alloy contains grains of solid solution of magnesium, lamellar precipitation of Al4Sr phase and massive-type phase. This phase was tentatively named Al3Mg13Sr and its crystal structure is not yet clearly determined. Paper presents the results of Rietveld fitting for AJ63 magnesium alloy and model of the crystal structure for Al3Mg13Sr compound.

Precipitation Prediction and Experimental Clarification of Mg-Al-Sn System

Phase equilibrium of the Mg-Al-Sn alloy system was calculated in detail by utilizing phase diagram calculation commercial package and other thermodynamic data for Mg alloys. The calculated phase diagrams were compared with the DSC results for the alloys of Mg-3wt%Al-3wt%Sn. The solidification and precipitation process of Mg-3wt%Al-Xwt%Sn were analyzed. The detailed comparison strongly supports the reliability of the selected thermodynamic description based on the results of thermodynamic calculation. It is clarified that when the Mg-Al-Sn alloy ends its solidification and cools down continuously, the phase Mg2Sn precipitated first from solid solution of magnesium, and then the Mg17Al12 phase precipitated at relative lower temperature. This is shown that the calculation phase diagram method considerably reduces the effort of alloy design and that the reliability of the results is high.

Mg–Gd–Y system phase diagram calculation and experimental clarification

Phase equilibrium of the Mg–Gd–Y system in Mg-rich corner was calculated in detail by phase diagram calculation software Pandat and thermodynamic database for Mg alloys. The calculated phase diagrams were compared with the key experimental results of DSC analysis for the alloys Mg–1 wt%Gd–7 wt%Y and Mg–5 wt%Gd–2 wt%Y. The solidification and precipitation process of the newly developed alloy Mg–12 wt%Gd–4 wt%Y–0.6 wt%Zr were analyzed. The detailed comparison strongly supports the reliability of the selected thermodynamic description based on the results of thermodynamic calculation. It is clarified that when the Mg–1Gd–7Y alloy ends its solidification and cools down continuously, the second phase Mg 24Y 5 firstly precipitated from solid solution of magnesium and then the GdMg 5 phase precipitated at relative lower temperature. But for Mg–5Gd–2Y alloy, the precipitation sequence of Mg 24Y 5 and GdMg 5 are in reverse order. Referring the calculated Mg–Gd–Y system phase diagrams, the suitable thermal mechanical processing and heat-treatment processes of newly designed and developed alloy Mg–12 wt%Gd–4 wt%Y–0.6 wt%Zr has been done.

Effect of Cerium and Yttrium on Aging Processes in Alloys of the Al – Mg System

The effect of small additives of rare earth metals (REM) (cerium and yttrium in an amount of about 0.6 wt.% each) on the decomposition of supersaturated solid solution of magnesium in aluminum in Al – Mg alloys bearing up to 16.6% Mg is studied in the process of natural and artificial aging. It is shown that the addition of REM delays the decomposition of the aluminum solid solution.

Fundamental Formation Laws of Phase Composition, Structure and Properties of Aluminium Materials Manufactured by Mechanical Alloying

The present investigation objective is to develop the technological process for strengthened aluminium alloys formation of different density based on mechanical alloying. Standard aluminium and magnesium powders were used as initial materials. Lithium was introduced in free state and binded in hydroxide LiOH. Granulated composition with mean particle size 0.2 ... 0.3 mm is the product of mechanical alloying. Thermal treatment of granulated compositions and hot compaction of semiproducts initiate phase transformations which contribute to thermodynamic equilibrium state of the alloys. Alloy base is characterized by micro- or small crystalline structure and presents a solid solution of magnesium and lithium in aluminium strengthened by nanocrystalline inclusions of aluminium oxides, magnesium and aluminium carbides which results in high strength of said alloys at low and high temperatures.

Lattice parameters of lithium-magnesium and lithium-silver alloys

The lattice parameters of solid solutions of magnesium and silver in lithium have been measured by X-ray diffraction, using extruded wire specimens. The results for the LiMg alloys are compared with some previously published values. In the dilute (<0.5 at%Ag)LiAg alloys, a very rapid change in the lattice parameter of -1.7 * 10-2 angstrom per at % Ag was found.

Genesis and Environment of Deposition of the Meagher Formation in Southwestern Montana

ABSTRACT The Meagher Formation conformably overlies the Wolsey Shale and can be divided into three distinct lithologic units. The lowest unit is a mixture of micrite and microsparite and locally includes significant amounts of argillaceous material, fossil debris, and calcispheres. The unit contains blue and gold mottling and irregular patches of dolomite. The middle unit is an oolitic, pelletoidal, intraclastic sparite. The allochems commonly form crossbedded sediments and exhibit incipient dolomitization. Recrystallization and dolomitization are evident in this unit but are not volumetrically abundant. The uppermost unit is characterized by thin blue and gold mottled beds of biosparite and locally contain pellets and algal pisolites. The deposition of the Meagher Formation took place on a stable shelf dotted by marine banks and shoals. Oolites formed in the more shallow, highly agitated waters in and around the banks, by a combination of accretion and/or precipitation, and abrasion processes. Fluctuations in sea level subjected these semiconsolidated sediments to sporadic wave attack, as attested to by intraclasts made up of all previously deposited carbonate sediments. Diagenetic alteration ranges from very slight to almost complete obliteration of original structure and texture in some parts of the Meagher Formation, as a result of dolomitization, recrystallization, and the formation of stylolites. Mottling in the Meagher Formation is classified into three types: depositionally controlled, organically controlled, and diagenetically controlled. Mottling, with the exception of the depositionally controlled type, is associated with dolomitization, recrystallization and iron-staining. Dolomitization related to mottling took place during the period of lithification when sea water was still incorporated in the semisolid sediment. Incipient dolomitization of allochems has been a product of diagenetic differentiation and has resulted from the unmixing of a solid solution of magnesium and calcium carbonate.