Thermal Conductivity Of Mg Research Articles

Effect of Cu addition on the thermal conductivity and mechanical properties of Mg–Zn-xCu-Ce alloys

Thermal conductivity and mechanical properties of Mg–Zn-xCu-Ce alloys with different Cu contents under low extrusion temperature were systematically investigated in this work. The results shows that MgZnCu and Ce-rich (Mg, Zn, Cu, Ce) phase were formed in Mg–Zn-xCu-Ce alloys with high Cu content, which have significantly effect on the thermal conductivity and dynamic recrystallization (DRX). The distribution of grain morphology and LAGBs indicates that CDRX is the main mechanism. The addition of Cu element has an inhibitory effect on the DRX behavior, greatly refining the DRXed grains. After extrusion, a large amount of nano-phase is dispersed in the MZEC alloy, which has a strong pinning effect on dislocations. The formation of MgZnCu phase with high thermal conductivity sacrifices the solute atoms of Zn and Cu in α-Mg matrix, which leads to reduction of lattice distortion of Mg matrix, thereby ensuring high thermal conductivity of Mg–Zn–Cu–Ce ternary magnesium alloys. With the increase of Cu content, the strength and thermal conductivity of the alloy gradually increases. When the Cu content is 3.6 wt%, UTS (ultimate tensile strength), YS (yield strength), EL (elongation) and thermal conductivity are 350 MPa, 317 MPa,15.8% and 135 W/m∙K, respectively.

The effects of substitution of yttrium for Ce-rich mischmetal on the mechanical properties and thermal conductivity of Mg–4Al–4Zn–4RE alloy

Mechanical properties and thermal conductivity are the key parameters for Mg alloys used as the structural components for heat dissipation, balancing good mechanical properties and high thermal conductivity is still a long-term challenge. Here, we investigated the influence of Y contents on the microstructure and mechanical properties of the as-cast Mg–4Al–4Zn–(4–x)RE–xY (x: 0, 1, 2, 3, 4 wt%), where RE was the Ce-rich misch metal. Compared with Mg–4Al–4Zn–4RE alloy, the strength and ductility were significantly enhanced due to the well-optimized microstructure by the suitable substitution of Y for Ce-rich RE. Especially, the ultimate tensile strength and elongation were significantly improved from 201 MPa to 244 MPa and 8.0% to 16.8%, respectively, when the Y content was increased from 0 to 3.0 wt%. Meanwhile, the thermal conductivity still kept a high level within the range of 84.2–89.6 W(m·K)−1. The significantly improved elongation was mainly attributed to the reduction and refinement of coarse lamellar Al11RE3 intermetallic phases with increasing Y contents. The as-cast Mg–4Al–4Zn–1RE–3Y alloy exhibited high performance with a combination of high tensile properties and good thermal conductivity.

Manipulating the mechanical strength and thermal conductivity of a Mg–4Zn-0.6Zr alloy through Ca addition

In this study, the microstructure, mechanical properties, and thermal conductivity of as-extruded Mg–4Zn-0.6Zr-xCa (x = 0, 0.3, 0.6, 0.9 wt%) alloys were investigated. The results revealed a bimodal grain size distribution in all the alloys due to incomplete dynamic recrystallization (DRX), characterized by the coexistence of elongated deformed grains and equiaxed DRX grains. The bimodal grain size distribution enhanced the mechanical properties of the studied alloys. Furthermore, Ca alloying facilitated the formation of Ca2Mg6Zn3 phases, through which the DRX extent was also enhanced. The precipitation of secondary phases, along with the increased DRX induced by Ca addition, was beneficial in eliminating the lattice distortion of the alloys, resulting in improved thermal conductivity compared to the Ca-free Mg–4Zn-0.6Zr alloy. The optimum combination of mechanical properties and thermal conductivity was achieved in the Mg–4Zn-0.6Zr-0.6Ca alloy, with yielding strength, ultimate tensile strength, tensile fracture elongation, and thermal conductivity values of 271 MPa, 318 MPa, 17.6 %, and 123.9 W/(m‧K), respectively. This work demonstrates that Mg–Zn–Zr–Ca-based alloys can be developed with high strength and high thermal conductivity, significantly expanding the industrial application of magnesium alloys.

Relationship between microstructure evolution and thermal conductivity of Mg–Sn–Ca alloys

Relationship between microstructure evolution and thermal conductivity of Mg–Sn–Ca alloys

Microstructure evolution and improvement of thermal conductivity in Mg–2Sn alloy induced by La addition

Rare earth elements are commonly used to improve the properties of magnesium alloys. In this paper, the effects of various La contents on the microstructure and thermal properties of Mg–2Sn alloys were investigated. Cooling curve thermal analysis technique was adopted to reveal the microstructure evolution of Mg-2Sn-xLa alloys. La addition contributed a new eutectic reaction to occur at 639 °C and the eutectic structure was determined to be LaMgSn phase. Mg12La, Mg2Sn and matrix precipitated phases may be generated in the microstructure with further increase of La content. The thermal conductivity of Mg–2Sn alloy can be effectively improved by La addition and the maximum value 149 W/(m·K) was achieved at the Sn/La atomic ratio of 1. The thermal conductivity of Mg-2Sn-2.3La alloy could further increase to 152 W/(m·K) after solution heat treatment. The addition of La reduced the amount of solute atoms and eliminated the Sn enriched region, resulted in a rapid increase in the thermal conductivity of the Mg–2Sn alloy. The spheroidization of Mg12La phase contributed to the further improvement of the thermal conductivity after solution treatment.

Thermodynamic prediction of thermal diffusivity and thermal conductivity in Mg–Zn–La/Ce system

• Heat dissipating Mg–Zn–La/Ce alloys were designed based on thermodynamic database. • τ 1 phases have more negative influence on thermal diffusivity than REMg 12 . • Solute atom is dominant factor affecting thermal conductivity of Mg–Zn–RE alloys. • The thermal diffusivities of Mg–Zn–La/Ce alloys were predicted by CALPHAD method. Basic thermal properties and mechanical properties are critical parameters for the structural magnesium alloys. Solute atoms and second phases can improve mechanical properties, but are deteriorating the heat dissipation performance. Through experimental determination of alloys, it is found that REMg 12 phases have fewer negative impacts on thermal diffusivities than τ 1 phases. With the same intermetallic compound, the solute atom Zn have more negative influences on thermal diffusivities of Mg–Zn–La/Ce alloys than the content of second phases. In order to quantitatively evaluate thermal conductivities and further design Mg alloys with both high strength and high thermal conductivity, a calculated method is provided to describe the thermal diffusivity of alloys as a function of alloy composition and phase constitution. A set of parameters for expression of thermal diffusivity of Mg–Zn–La/Ce alloys were obtained through assessing the experimental data. The thermal conductivities of Mg–Zn–La/Ce system were predicted and agreed well with experimental values with calculation error of 1.6% and standard error of ±3.0 W/(m K). The calculation method considering thermal diffusivity resistivity improves the calculation accuracy and would be physically significant.

High‐Density Frenkel Defects as Origin of N‐Type Thermoelectric Performance and Low Thermal Conductivity in Mg3Sb2‐Based Materials

AbstractMg3Sb2‐based intermetallic compounds with exceptionally high thermoelectric performance exhibit unconventional n‐type dopability and anomalously low thermal conductivity, attracting much attention to the underlying mechanisms. To date, investigations have been limited to first‐principle calculations and thermodynamic analysis of defect formation, and detailed experimental analysis on crystal structure and phonon modes has not been achieved. Here, a synchrotron X‐ray diffraction study clarifies that, against a previous view of a simple crystal structure with a small unit cell, Mg3Sb2 is inherently a heavily disordered material with Frenkel defects, charge‐neutral defect complexes of cation vacancies and interstitials. Ionic charge neutrality preserved in Mg3Sb2 is responsible for exotic n‐type dopability, which is unachievable for other Zintl phase materials. The thermal conductivity of Mg3Sb2 exhibits deviation from the standard T−1 temperature dependency with strongly limited phonon transport due to a strain field. Inelastic X‐ray scattering measurement reveals enhanced phonon scattering induced by disorder. The results will draw renewed attention to crystal defects and disorder as means to explore new high‐performance thermoelectric materials.

Microstructure and thermophysical properties of Mg−2Zn−xCu alloys

Abstract The microstructure and thermophysical properties of Mg−2Zn−xCu alloys (x=0.5, 1.0 and 1.5, at.%) were investigated through microstructural and thermophysical characterization, heat treatment, and first-principles calculations. It was found that the addition of Cu had influence on the microstructure and thermophysical properties of the alloy. As the Cu content increased, the content of the MgCuZn phase increased in the as-cast alloys along with the electrical and thermal conductivities. After solution treatment, the eutectic structure partially decomposed and Zn atoms dissolved into the matrix, leading to the decrease in both the electrical and thermal conductivities of the alloy. During the early stages of the aging treatment, solute atoms precipitated from the matrix, thus increasing the electrical conductivity of the alloy. After aging for 24 h, the thermal conductivity of Mg−2Zn−1.5Cu alloy reached the maximum of 147.1 W/(m·K). The thermostable MgCuZn phases were responsible for increasing the electrical and thermal conductivities. Smaller amounts of Zn atoms dissolved in the matrix resulted in smaller lattice distortion and higher conductivities. The first-principles calculations findings also proved that the MgCuZn phases had very high conductance.

Reduced Thermal Conductivity of Mg2(Si, Sn) Solid Solutions by a Gradient Composition Layered Microstructure.

Solid solutioning of Mg2(Si, Sn) has been a promising approach in reducing thermal conductivity and leads to improvement of thermoelectric performance. In addition to the Mg2(Si, Sn) solid solutions, we have noticed a layered structure with a gradient composition, which is formed by nonequilibrium solidification and peritectic reaction process and can provide further reduction of thermal conductivity of the Mg2(Si, Sn) solid solutions. All layers of the layered structure have the same face-centered cubic-based structure but varying Sn/Si concentration ratios in each layer. The interfaces between the layers are semi-coherent, reticulating with different numbers of misfit dislocations. Such an interfacial structure brings large numbers of phonon-scattering sources, resulting in further reduction of thermal conductivity in the Mg2(Si, Sn) solid solutions. Consequently, the undoped Mg2Si0.75Sn0.25 containing a higher density of the layered structure has relatively lower thermal conductivity, 1.9 W m-1 K-1 at 523 K, than Mg2Si0.25Sn0.75 with a much lower density of the layered structure, 2.3 W m-1 K-1 at 523 K.

Microstructure, Thermal Conductivity and Mechanical Properties of the Mg–Zn–Sb Ternary Alloys

A novel Mg alloys of Mg–xZn–ySb (x = 0, 2, 4, 6; y = 0, 0.2, 0.5, 0.8, 1.2) were designed and their microstructure, thermal conductivity and mechanical properties were systematically investigated in the present study. The as-cast Mg–Zn–Sb ternary alloys consist of α-Mg, Mg4Zn7 and Mg3Sb2 phases. Sb addition can refine the eutectic structure (α-Mg + Mg4Zn7) by the growth of Mg4Zn7 on Mg3Sb2 phases. The thermal conductivity of Mg–Zn–Sb alloys decreased with increasing Sb content. There existed an interactive effect of Zn/Sb on the thermal conductivity of the Mg–Zn–Sb alloys. The negative effect of Sb addition on thermal conductivity of alloys was getting smaller with increasing Zn content in alloys. The negative effect of Mg3Sb2 phases on the thermal conductivity of alloys could be weakened by the formation of weak-scattering Mg4Zn7 coated on Mg3Sb2 phases. The best refinement effect on microstructure could be obtained with 0.8 wt%Sb addition. Mg–4Zn–0.8Sb alloy possess the best comprehensive properties with thermal conductivity of over than 120 W/(m·K) and UTS of 185.6 MPa.

A review on thermal conductivity of magnesium and its alloys

Abstract This review summarizes recent researching works the thermal conductivity of Mg–Zn, Mg–Al, Mg–Mn and Mg–RE alloys. Solute atoms, heat treatment, deformation and temperature, which have significant influence on the thermal conductivity of magnesium alloys, are highlighted. For an individual solute atom, its effects on thermal conductivity are highly dependent on its chemical valence, radius and extra-nuclear electrons. The thermal conductivity of Mg alloys is decreased by solution treatment, but improved by aging and/or annealing treatments. As for the deformed Mg alloys, the thermal conductivity along transverse or normal direction is superior to that of along extrusion or rolling direction. We expect this review is helpful for those who are working on developing Mg alloys with superior thermal conductivity.

Effect of La content on microstructure, thermal conductivity and mechanical properties of Mg–4Al magnesium alloys

Microstructure, thermal conductivity and mechanical properties of Mg–4Al-xLa (x = 2, 4, 6 wt%) were investigated. The concentration of Al dissolved in α-Mg matrix decreases with the increase of La content, and the volume fraction of Al11La3 in the Mg–4Al-xLa alloys increases because La tends to consume Al to form Al11La3. As a consequence, both yield strength and thermal conductivity of the Mg–4Al-xLa alloys in as-cast condition increase with the increasing La content. After extrusion, both thermal conductivity and mechanical properties of the Mg–4Al-xLa alloys further increase due to dynamic precipitation of Al11La3 which consumes the Al solutes dissolved in the α-Mg. The extruded Mg–4Al–6La alloy exhibits high thermal conductivity of 130 W/m·K, ultimate tensile strength (UTS) of 337 MPa, yield strength of 256 MPa and elongation to failure of 8.4%.

Thermal conductivity of the Mg–Al–Zn alloys: Experimental measurement and CALPHAD modeling

Thermal conductivity in a series of annealed Mg–Zn, Al–Zn and Mg–Al binary alloys was studied by experimental investigation and CALPHAD (CALculation of PHAse Diagram) methodology. Microstructure and phase identification of the alloys were determined using scanning electron microscopy and X-ray diffraction techniques. Thermal conductivity was measured over the temperature ranges from 298 K to 498 K on a Netzsch LFA457 using laser flash method. Based on the obtained experimental data, the mechanism of thermal conductivity variation was proposed. Considering the available experimental data from literature and the present work, the thermal conductivities of the Mg–Al–Zn system including pure elements, intermetallics, solid solution phases and two-phase regions were evaluated using the CALPHAD method (CALculation of PHAse Diagram). A set of self-consistent parameters for description of the thermal conductivity in Mg–Al–Zn system was obtained. The calculated results using the obtained parameters and the available experiment data shows an excellent consistency.

Effect of solute atoms and second phases on the thermal conductivity of Mg-RE alloys: A quantitative study

In this study, the room temperature thermal conductivity and microstructure of Mg−Ce, Mg−Sm and Mg−Y binary alloys in as-cast and solution treated conditions were investigated. Quantitative study was conducted on the effect of rare earth elements (in solid solution and intermetallic compounds) on the thermal conductivity of Mg−RE alloys. The reduction in thermal conductivity was determined to be about 123.0 W/(m·K) and 6.5–16.4 W/(m·K), respectively, per 1 at.% RE addition in the form of solid solution or intermetallic compounds with Mg. The thermal conductivities of Mg−RE alloys were fitted using modified Maxwell and EMT models based on the distribution, volume fractions and shape of intermetallic compounds. The modified structural models provide a good fit to the experimental thermal conductivity data.

Effects of precipitates and its interface on thermal conductivity of Mg–12Gd alloy during aging treatment

How to simultaneously improve the thermal conductivity and mechanical properties of Mg alloys is an interesting and important issue topic. In the present study, the effect of aging treatment on the thermal conductivity and micro-hardness of Mg–12Gd alloy was investigated. Results indicated that the thermal conductivity and micro-hardness of the alloy could be significantly improved by aging treatment, and Mg–12Gd alloy exhibited a typical aging hardening response with the increasing aging time. At the early stage of aging (4 h), a large number of fine particles precipitated from α-Mg matrix, but thermal conductivity of alloy increased a little, which was attributed to the coherent interface hindering the increase of thermal conductivity. The thermal conductivity increased to the peak value of 75.7 W/(m·K) at the aging time of 300 h, which was about 2.17 times that of as-solutionized alloy. The huge increment in the thermal conductivity of as-aged Mg–12Gd alloy was related to the precipitation of particles and the incoherent interface between precipitates and α-Mg matrix.

An experimental and theoretical investigation on heat transfer capability of Mg (OH)2/MWCNT-engine oil hybrid nano-lubricant adopted as a coolant and lubricant fluid

The major objective of the present study is to investigate the heat transfer capability of Mg (OH)2/MWCNT- engine oil hybrid nano-lubricant. First, the effects of temperature and Solid volume fraction on the dynamic viscosity and thermal conductivity of Mg (OH)2/MWCNT- engine oil hybrid nano-lubricant have been experimentally investigated. The experiments have been conducted in various temperatures (25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, and 60 °C) and solid concentrations (0.25%, 0.5%, 0.75%, 1%, 1.5%, and 2%). Based on the measurements, it is found that the studied nano-lubricant showed Newtonian behavior in all the studied temperatures and solid concentrations. Furthermore, the experimental results indicated that the dynamic viscosity of the nano-lubricant increases with an increase in solid concentration while it decreases with an increase in temperature. The thermal conductivity of the nanofluid showed increasing trend as the solid concentration and temperature increased. The minimum and maximum enhancement were about 13% and 50%, respectively. Based on experimental data, two new trustworthy correlations to predict the dynamic viscosity and thermal conductivity of the nano-lubricant has been proposed. Finally, the heat transfer capability of the nanofluid has been theoretically investigated in both the internal laminar and turbulent flow regimes and it is found that the studied nanofluid can be advantageous in heat transfer applications.

The effect of surfactant and sonication time on the stability and thermal conductivity of water-based nanofluid containing Mg(OH)2 nanoparticles: An experimental investigation

The main objective of the present study was to investigate the effect of surfactant and sonication time on the stability and thermal conductivity of Mg (OH)2-water nanofluid over the different solid concentrations (0.1, 0.2, 0.4, 0.8, 1, 1.5, and 2%) and temperatures (25, 30, 35, 40, 45, 50°C). The nanofluid has been prepared using two-step method and applying different sonication time (10, 30, 50, 80, and 160min). Furthermore, three different surfactants (CTAB, SDS, Oleic Acid) have been added during the preparation process so as to investigate which surfactant shows better impact on the stability of the nanofluid. The results of Zeta potential analysis indicated that CTAB surfactant shows the best impact on the stability of the nanofluid applying 30-min sonication. Furthermore, it is found that the relative thermal conductivity of the studied nanofluid relatively increased as the solid concentration and temperature increased. The maximum increase in thermal conductivity took place at the solid concentration of 2% and temperature of 50°C by approximately 28%. Moreover, in order to investigate the effect of sonication time of thermal properties of the nanofluid, the relative thermal conductivity of the nanofluid versus sonication time in different solid concentrations and at the temperature of 30°C has been measured. The results indicated that the relative thermal conductivity showed decreasing trend as the sonication time increased in all the selected solid volume fractions.

Analysis of Microstructure and Thermal Conductivity in Mg–Sn–Ca Alloy

Analysis of Microstructure and Thermal Conductivity in Mg–Sn–Ca Alloy

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

Effects of Sn, Ca additions on thermal conductivity of Mg matrix alloys

In the present work, the effects of Sn, Ca additions on thermal conductivity were investigated in as cast Mg–Sn–Ca alloys. The measured values of thermal conductivity of Mg–3Sn–xCa alloys obviously increased from 85.6 to 126.3 W m− 1 K− 1 with the increasing Ca from 0 to 1.5 wt-%, and then decreased to 98.3 W m− 1 K− 1 with the 2.5 wt-% Ca. In addition, the thermal conductivity of the Mg–Sn–Ca (Sn/Ca atomic ratio of 1) alloys decreased slightly from 154.2 to 132.1 W m− 1 K− 1 with the increasing Sn, Ca. Meanwhile, the microstructures of the selected alloys were discussed in detail, suggesting that the solute atoms that caused lattice distortion had greater effect on thermal conductivity compared with the second phases formed in as cast Mg–Sn–Ca alloys.