Microstructure and Thermal Conductivity of As-Cast and As-Solutionized Mg–Rare Earth Binary Alloys

The microstructure and thermal conductivity of four groups of Mg–rare earth(RE) binary alloys(Mg–Ce,Mg–Nd, Mg–Y and Mg–Gd) in as-cast and as-solutionized states were systematically studied. Thermal conductivity was measured on a Netzsch LFA457 using laser flash method at room temperature. Results indicated that for as-cast alloys, the volume fraction of second phases increased with the increase of alloying elements. After solutionizing treatment, a part or most of second phases were dissolved in α-Mg matrix, except for Mg–Ce alloys. The thermal conductivity of as-cast and as-solutionized Mg–RE alloys decreased with the increase of concentrations. The thermal conductivity of as-solutionized Mg–Nd,Mg–Y and Mg–Gd alloys was lower than that of as-cast alloys. Thermal conductivity of as-solutionized Mg–Ce alloys was higher than that of as-cast alloys, because of the elimination of lattice defects and fine dispersed particles during solutionizing treatment. Different RE elements have different influences on the thermal conductivity of Mg alloys in the following order: Ce Nd Y Gd. Ce has the minimum effect on thermal conductivity of Mg alloys, because of the very low solubility of Ce in the α-Mg matrix. The variations in the atomic radius of the solute elements with Mg atom( r), valence, configuration of extranuclear electron of the solute atoms, and the maximum solid solubility of elements in the α-Mg matrix were suggested to be the main reasons for the differences in thermal conductivity of resulting Mg–RE alloys.     

Correlation on the Electrical and Thermal Conductivity for Binary Mg–Al and Mg–Zn Alloys

In this work, the electrical resistivity and thermal conductivity of both as-solution binary Mg–Al and Mg–Zn alloys were investigated from 298 K to 448 K, and the correlation between the corresponding electrical conductivity and thermal conductivity of the alloys was analyzed. The electrical resistivity of the Mg–Al and Mg–Zn alloys increased linearly with composition at 298 K, 348 K, 398 K, and 448 K, while the thermal conductivity of the alloys exponentially decreased with composition. Moreover, the electrical resistivity and thermal conductivity for both Mg–Al and Mg–Zn alloys varied linearly with temperature. On the basis of the Smith–Palmer equation, the thermal conductivity of both binary Mg alloys was found to be correlated quite well with the electrical conductivity in the temperature range from 298 K to 448 K. The corresponding Lorenz number is equal to $2.162\times 10^{-8} \,\hbox {V}^{2}\cdot \hbox {K}^{-2}$ 2.162 × 10 - 8 V 2 · K - 2 , and the lattice thermal conductivity is equal to $5.111 \,\hbox {W}\cdot \hbox {m}^{-1}\cdot \hbox {K}^{-1}$ 5.111 W · m - 1 · K - 1 . The possible mechanisms are also discussed.     

Thermal Conductivity and Thermal Diffusivity of Liquid Indium–Tin Alloys

Thermal-conductivity and thermal-diffusivity coefficients of indium–tin alloys have been determined using the laser flash method over the temperature range from the liquidus line to 1173 K. Measurements were performed using the setup LFA-427 of NETZSCH company in an argon protective atmosphere, and cells were produced from molybdenum. The equations for temperature dependences of the thermal conductivity and thermal diffusivity of In–Sn alloys have been obtained. The results of measurements were compared with data available in the literature.     

Thermal Conductivity and Thermal Diffusivity of Pulse-Heated W–Re Alloys

Results are reported for the thermal conductivity and thermal diffusivity as a function of temperature for four W–Re alloys (4.0, 21.24, 24.07, and 31.09 mass% of Re) over a wide temperature range covering the solid and liquid states. The measurements allow the determination of specific heat and dependences among electrical resistivity, temperature, and density of the alloys into the liquid phase. The thermal conductivity is calculated using the Wiedeman–Franz law. Additionally, data for thermal conductivity and thermal diffusivity of the constituent elements, tungsten and rhenium, are presented for the first time. Both metals have been previously studied with the same experimental technique.     

Microstructure and Properties of As-Cast Mg–2.0Sn–1.0Zn–1.0Y–0.3Zr Alloys at Different Extrusion Ratios

Herein, the effect of hot extrusion with different extrusion ratios (λ = 6, 8, 10, and 12) on the microstructure evolution and properties of as-cast Mg–2.0Sn–1.0Zn–1.0Y–0.3Zr magnesium alloys, using optical microscopy (OM), scanning electron microscopy (SEM), immersion corrosion and electrochemical corrosion experiment, and tensile testing, is investigated. The results show that the Mg₁₄SnY and Mg₆SnY precipitated phases exist in the alloy before and after extrusion. After hot extrusion, the second phase of the alloy is broken into particles along the extrusion direction, whereas the grain size is significantly reduced, and dynamic recrystallization and deformed grains exist in the microstructure. The mechanical properties of the extruded alloy improve, but the corrosion resistance weakens. When the extrusion ratio is λ = 10, the extruded alloy exhibits relatively good mechanical properties and corrosion resistance. The corrosion behaviors of the extruded alloys are affected by both the grain size and galvanic corrosion. In the initial stage of corrosion, intergranular corrosion plays a major role in reducing the corrosion resistance of the extruded alloys. With prolonged corrosion time, galvanic corrosion has a more significant effect on weakening the corrosion resistance of the extruded alloys.     

Corrosion Properties of Oxide Ceramic Coatings Based on Alloys of the Al–Cu–Mg and Al–Mg Systems

Materials Science - By the methods of electrochemical impedance spectroscopy and potentiodynamic methods, we estimate the corrosion resistance of oxide ceramic coatings obtained on...     

Microstructures, mechanical properties and in vitro corrosion behaviour of biodegradable Mg–Zr–Ca alloys

The microstructures, mechanical properties, corrosion behaviour and biocompatibility of the Mg–Zr–Ca alloys have been investigated for potential use in orthopaedic applications. The microstructures of the alloys were examined using X-ray diffraction analysis, optical microscopy and scanning electron microscopy. The mechanical properties of Mg–Zr–Ca alloys were determined from compressive tests. The corrosion behaviour has been investigated using an immersion test and electrochemical measurement. The biocompatibility was evaluated by cell growth factor using osteoblast-like SaOS2 cell. The experimental results indicate that the hot-rolled Mg–Zr–Ca alloys exhibit much finer microstructures than the as-cast Mg–Zr–Ca alloys which show coarse microstructures. The compressive strength of the hot-rolled alloys is much higher than that of the as-cast alloys and the human bone, which would offer appropriate mechanical properties for orthopaedic applications. The corrosion resistance of the alloys can be enhanced significantly by hot-rolling process. Hot-rolled Mg–0.5Zr–1Ca alloy (wt %) exhibits the lowest corrosion rate among all alloys studied in this paper. The hot-rolled Mg–0.5Zr–1Ca and Mg–1Zr–1Ca alloys exhibit better biocompatibility than other studied alloys and possess advanced mechanical properties, corrosion resistance and biocompatibility, suggesting that they have a great potential to be good candidates for orthopaedic applications.     

Thermal properties of Mg–Li and Mg–Li–Al alloys

Abstract

The present work is a study of the thermal properties of Mg–xLi–y Al with x= 4, 8 and 12 wt-% and y= 0, 3 and 5 wt-% as a function of temperature in the range 20–375°C. The thermal diffusivity and coefficient of thermal expansion (CTE) have been measured and the thermal conductivity calculated. The thermal diffusivity of all alloys decreases with an increasing content of lithium. The CTE of the single phase alloys Mg–4Li and Mg–12Li has a linear character, and the CTE of Mg–12Li is higher than that of Mg–4Li. The influence of thermal stresses in the two phase alloy Mg–8Li is perceptible in terms of temperature dependence of the CTE. In Mg–4Li–3Al and Mg–4Li–5Al, an influence of the solution of AlLi phase on all the studied thermal properties has been found.     

Enhancing mechanical properties of Mg–Sn alloys by combining addition of Ca and Zn

We developed new wrought Mg–2Sn–1Ca wt.% (TX21) and Mg–2Sn–1Ca–2Zn wt.% (TXZ212) alloys with high strength and ductility simultaneously, produced by conventional casting, homogenization and indirect extrusion. A partial dynamically recrystallized microstructure, with the micron-/nano-MgSnCa particles and G.P. zones dispersing, was obtained in TX21 alloy extruded at 260 °C (TX21-260). The TX21-260 alloy exhibited yield strength (YS) of 269 MPa, ultimate tensile strength (UTS) of 305 MPa, while those of the TX21 alloy extruded at 300 °C decreased to be 207 MPa and 230 MPa respectively. For TXZ212-260 alloy, on the other hand, MgSnCa, MgZnCa and MgZn₂ phases were observed, and the average grain size increased to be ∼5 μm. The YS and UTS of TXZ212-260 alloy evolved to be 218 MPa and 285 MPa, and the elongation (EL) reached as high as 23%. The high strengths of TX21-260 alloy were expected due to the high number density of nano-MgSnCa phases, G.P. zones and ultra-fine grain size (∼0.8 μm). The high EL of 23% in TXZ212-260 alloy was consistent with the high work-hardening rate, which was attributed to the larger grain size, more high angular grain boundaries, presence of more nano-particles and the weaker texture.     

Formation and thermal stability of Ca–Mg–Zn and Ca–Mg–Zn–Cu bulk metallic glasses

Several Ca–Mg–Zn and Ca–Mg–Zn–Cu bulk metallic glasses were produced by copper mold casting method. The alloy compositions were selected using specific criteria recently identified by the authors. The glass transition temperature, crystallization temperature, temperature interval of the supercooled region, melting temperature as well as heats of crystallization, and melting are reported for these alloys.     

Thermodynamic Properties of Si–Ge and Si–Sn Melts

The mixing enthalpies of Si–Ge and Si–Sn liquid alloys were measured in an isoperibolic calorimeter. The results demonstrate that the formation of Si–Ge melts is accompanied by a small heat release, while the formation of Si–Sn melts is an endothermic process. Calculations of the Si activity in Si–Sn melts by Schroeder's equation indicate large positive deviations from Raoult's law.     

Effects of Sr and Sn on microstructure and corrosion resistance of Mg–Zr–Ca magnesium alloy for biomedical applications

Magnesium based alloy is a biodegradable metal that has significant potential advantages as an implant material. Element alloying is one of the effective methods to modify the performance of the magnesium alloy. In the paper, Sr and Sn as alloy elements were simultaneously added into the Mg–Zr–Ca alloy to improve the corrosion resistance. The differences of Mg–Zr–Ca alloy and Mg–Zr–Ca–Sr–Sn alloy were compared. The X-ray diffractometer (XRD) and the scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) were used to analysis the phases and the microstructure of the alloys. The results indicated that the addition of Sn could form Mg₂Sn mainly within the grain interior; Sr phase was mainly detected along the grain boundary. Immersion tests and electrochemical measurements showed that the corrosion resistance was improved obviously with simultaneous addition of Sr and Sn in Mg–Zr–Ca alloy. It suggested that bio-magnesium based alloy can use Sr and Sn as effective alloy elements to modify its performance.     

Influence of Small Cr Addition on Thermal Stability and Magnetic Properties of Fe-Co-Zr-Nb-B Glassy Alloys

Fe62Cos-xCrxZr6Nb4B20 （x=0-4 at. pct） metallic glasses show high thermal stability with a maximum supercooled liquid region of about 84.8 K. The addition of 2 at. pct Cr causes the extension of the supercooled liquid region remarkably, leading to the enhancement of thermal stability and glass-forming ability. The crystallization of the Fe-based glassy alloys takes place through a single exothermic reaction, accompanying the precipitation of more than three kinds of crystallized phases such as α-Fe, Fe2Zr and ZrB2. The long-range atomic rearrangements required for the precipitation of the multiple crystalline phases seem to play an important role in the appearance of the large supercooled liquid region through the retardation of the crystallization reactions. The Fe-based alloys exhibit soft ferromagnetic properties. The saturation magnetization decreases with increasing Cr content while the saturated magnetostriction increases as a function of Cr content. There is no distinct change in the saturation magnetization and coercive force with annealing temperature below the crystallization temperature. The devitrification gives rise to a considerable enhancement in both as and He.