Electrical Resistivity and Thermal Conductivity of Pure Aluminum and Aluminum Alloys up to and above the Melting Temperature (original) (raw)
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2010
The variations of thermal conductivity with temperature for Al-[x] wt.% Cu, x = 3, 6, 15 and 24 alloys were measured by using a radial heat flow apparatus. The variations of electrical conductivity of solid phases versus temperature for the same alloys were determined from the Wiedemann-Franz and Smith-Palmer equations by using the measured values of thermal conductivity. From the graphs of thermal and electrical conductivity versus temperature, the thermal conductivity of the solid phases at their melting temperatures, and the thermal temperature and the electrical coefficients for the same alloys were obtained. Dependency of the thermal and electrical conductivity on the composition of Cu in the Al based AlÀCu alloys were also investigated. According to present experimental results, the thermal and electrical conductivity of Al-[x] wt.% Cu, x = 3, 6, 15 and 24 alloys linearly decrease with increasing the temperature and composition of Cu. The enthalpy of fusion and the specific heat change during the transformation for the same alloys were determined from cooling trace during the transformation from eutectic liquid to eutectic solid by means of differential scanning calorimeter (DSC).
Selection of electrodes for the ˝in situ˝ electrical resistivity measurements of molten aluminium
The aim of this paper is the selections of proper electrode material for four-probe technique electrical resistivity measurement of aluminium and aluminium alloys. The biggest problem of electrodes is oxidation during measurement causing high contact resistance and giving wrong results. Various materials have been tested and aluminium electrodes have been chosen. Advantage of aluminium electrodes is that they are melted in specimen right after the pouring and causing no interface which is resulting with any contact resistance. The device together with measuring cell for ˝in situm easurement of electrical resistivity was developed using four-probe DC technique.
MEASURING THE EFFECT OF ADDING COPPER ON THE QUALITY OF THE THERMAL CONDUCTIVITY OF PURE ALUMINUM
In this research, an experimental work had been conducted to measure the effect of adding copper (Cu) with different percentages to the pure Aluminum (AL) and noise variables (error) on the quality of thermal conductivity (k). Alloys had been prepared by changing percentages addition of copper to pure Aluminum and the percentages were (5, 10, 15, 20&25%). The effect of an average deviation and variability on the thermal properties after an addition of copper through use of normal probability plot. The results shows as that copper percentage was increasing lead to increase thermal conductivity by (15.47%) and the property of thermal conductivity had goodness of fit test and percentages the effect of adding copper to pure Aluminium (AL) and error were (97%, 3%) respectively.
Electrical resistivity measurements of Al-cast alloys during solidification
International Journal of Microstructure and Materials Properties, 2015
The aim of this paper was the selection of proper electrodes material regarding four-probe technique for the electrical resistivity measurements of Al-Si cast alloys. The most significant problem for electrodes is oxidation during measurements causing high contact resistance and providing incorrect results. Various materials were tested and aluminium electrodes chosen. The advantage of aluminium electrodes is that they melt within the specimen immediately after being poured and cause no interface resulting with any contact resistance. Pure aluminium and eutectic AlSi12 alloys were tested. Resistivity of Al-Si alloys is increasing with Si content. Grain refinement and modification of Si were employed. Grain refinement has any effect on electrical resistivity. Modification of Si phase causes decrease of electrical resistivity.
Thermal and electrical conductivity in Al–Si/Cu/Fe/Mg binary and ternary Al alloys
Journal of Materials Science, 2015
This study investigated 30Al-Si, Al-Cu, Al-Fe, Al-Mg, Al-10Si-Cu, Al-10Si-Fe, and Al-10Si-Mg binary and ternary Al alloys, which are among the most commonly used commercial alloys. The thermal and electrical conductivity of the gravity castings of these alloys were measured. The results indicated that when 1 wt% Si, Cu, or Fe was mixed with commercial Al with 99.8 % purity, the thermal conductivity decreased from 213.5 Wm −1 K −1 to approximately 190-210 Wm −1 K −1. The thermal conductivity remained at a nearly constant level of 154-157 Wm −1 K −1 when the Si concentration exceeded 6 wt% in the Al-Si alloys. Regarding the Al-Mg alloys, the thermal conductivity did not change when the concentration of Mg was increased to 1 wt%. When the concentration of Mg exceeded 1 wt%, the thermal conductivity decreased greatly from 212.1 Wm −1 K −1 in the Al-1wt%Mg to 124.1 Wm −1 K −1 in the Al-5wt%Mg. This decrease occurred because the Mg-rich phase continuously impeded heat transfer at the grain boundaries. For the ternary Al alloys, when 0-1 wt% Fe or Cu was added to Al-10Si, the thermal conductivity increased slightly from 154 Wm −1 K −1 in Al-10Si to 162.7 Wm −1 K −1. The increase was due to the inclusion of Fe, which led to the formation of an Al x Fe y Si phase, reducing the solutes in the matrix phase. When the composition, morphology, amount, and distribution of all precipitates along with the matrix phase were taken into account, the effective medium approximations accurately interpreted the thermal conductivities of the Al alloys. Electrical conductivities were also measured and compared with thermal conductivities estimated using the Wiedemann-Franz law, and the results indicated close agreement. The Wiedemann-Franz law, however, often underestimates the thermal conductivity in Al alloys containing a high level of Si.
Thermal conductivity of liquid metals and metallic alloys
Journal of Non-Crystalline Solids, 1999
The aim of this work is to show that the electrical resistivity and the thermoelectric power can be used to determine the thermal conductivity of liquid metals and alloys. We have made this determination for liquid aluminum, tin, lead, copper and metallic alloys Cu±Al, Ag±Ga, Ag±Ge, Cu±Pb, In±Mn, Ga±Ge and Sn±Bi. For these calculations, we used the relations between the transport coecients that can be simpli®ed to the Wiedemann±Franz law. For the pure metals studied, our calculated thermal conductivities are near experimental determinations from dierent authors, showing that the Wiedemann±Franz law is valid. We predict that the Al±Cu liquid alloy has a minimum in the thermal conductivity, and in its temperature coecient versus concentration at 20 at.% of aluminum. This result is in agreement with the magnetic susceptibility data, and with the super®cial tension that have unusual magnitudes near this concentration. It is also consistent with the existence of an eutectic near the same concentration. Nevertheless, it is in contradiction with other data also deduced from resistivity measurements. We do not have any explanation of that disagreement. We show that a minimum in the thermal conductivity isotherm is also obtained for other noblepolyvalent liquid metal alloys studied, i.e. Ag±Ga and Ag±Ge. The only exception is the Cu±Pb alloy for which the calculated thermal conductivity varies monotonically with concentration. Ó
International Journal of Thermophysics, 2006
New measurements of the thermal conductivity of molten mercury, gallium, tin, and indium are reported up to 750 K. The measurements are performed in a novel transient hot-wire instrument described elsewhere. The present experimental technique overcomes problems of convection, and it is shown that it operates in an absolute way in accord with a theoretical model. The uncertainty of the
International Journal of Heat and Mass Transfer, 2017
In this study, the effects of casting processes and heat treatments on the thermal conductivity of an Al-10 wt% Si-0.6 wt% Cu-0.9 wt% Fe-0.7 wt% Zn aluminum alloy were studied. Both gravity-and die-casting processes were used. The porosity in die castings was controlled by varying the injection pressure and plunger velocity. The porosity, microstructures, and thermal and electrical conductivities of the die castings were characterized. The thermal conductivity of gravity-cast material achieved 143.4 W m À1 K À1 , whereas those of die-cast materials ranged from 110.8 to 126.8 W m À1 K À1. The die-cast aluminum alloys demonstrated considerably finer interconnecting precipitates than did the gravity castings. The closely spaced precipitates acted as barriers for thermal conduction, leading to reduced thermal conductivity. Die-casting pressures and velocities were controlled to form die castings with up to 3.73% porosity, which led to a 12.6% decrease in thermal conductivity. The die-cast Al alloys were then subject to solutionization (T4) and aging treatments (T6). The silicon precipitates were spheroidized, thus widening the paths for heat conduction. The thermal conductivity was greatly enhanced, increasing from 126.8 W m À1 K À1 in the die-cast condition to 151.6 W m À1 K À1 after 550°C solutionizing and 4 h of aging at 200°C. The thermal conductivity of the gravity-cast materials remained unchanged after the same heat treatments. Improving the thermal conductivity of die castings through proper heat treatments is crucial for aluminum alloys in rigorous heat-dissipating applications.
Manufacturing Technology, 2018
Electrical conductivity depends significantly on a structural state. It can be influenced by chemical composition, content of alloying elements, presence of different types of phases and dislocation substructure as well. Therefore, the relation between electrical conductivity and mechanical properties is very interesting from a material point of view. In combination with structural analyses (metallography, electron microscopy), important information about materials structures and their changes as a function of various factors (deformation, heat treatment) can be obtained. The present paper describes the role of electrical conductivity measurements during an investigation of the effect of technological parameters on the structure and properties of aluminium alloys.