Microstructure and Thermal Resistance of As-Cast Mg-xDy Alloys AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY21010020

Chinese Library Classification Number:TG146.22

Citation Information:

Magnesium alloys are widely used in aerospace and other aircraft equipment due to their lightweight advantages. These aircraft will rub against the air during high-speed operation and generate a lot of heat, so magnesium alloys are required to be able to serve at higher temperatures. This requires that the magnesium alloy must have a certain thermal resistance, reduce the speed of heat transfer during the operation of the equipment, and extend its service time under high temperature conditions. At present, improving the thermal resistance of magnesium alloys is mainly achieved by coating thermal barrier coatings (TBCs), but there are also many problems and defects in the use of thermal barrier coatings. Firstly, the coating will crack and fall off during the service process；secondly, the use of the coating will increase the economy and time cost；thirdly, the use of the coating cannot meet the requirements for lightweight materials. Therefore, in order to improve the heat resistance of magnesium alloys and reduce the adverse effects brought by thermal barrier coatings, it is very necessary to study the intrinsic heat resistance of magnesium alloys. This paper took Mg-xDy (x=0.5, 1.4, 2.3；%, atom fraction) alloy as the research object, studied the microstructure changes of Mg-Dy alloy with different contents, and calculated its corresponding thermal resistivity, revealing the influence of Dy content on the thermal resistance of as-cast alloys. The microstructure observation and heat resistance test of Mg-xDy alloy with different contents were carried out. The phase of the alloy was analyzed by XPERT-PRO polycrystal diffractometer, the scanning range was 10°~90°, the target was a Cu target, and the acceleration voltage and current were 40 kV and 40 mA, respectively. JSM-7610F scanning electron microscope (SEM) with energy spectrometer (EDS) was used to observe the backscattering microstructure and micro-area composition analysis. The thermal diffusivity (α) and specific heat capacity (C_p) of the alloy were tested on the LFA-467 laser flasher, and the density (ρ) was measured by the Archimedes method. According to the thermal conductivity calculation formula λ=α·ρ·C_p, the thermal conductivity of the alloy was obtained, and the thermal resistivity of the alloy was obtained by further calculation. The results showed that：Mg-xDy alloys were mainly composed of α-Mg, Mg₃Dy phases and enrichment area of Dy element. The second phase was segregated at the grain boundary, and most of Mg₃Dy phase was attached to the enrichment area of Dy element. With the addition of Dy, the solid solution Dy atoms in the matrix increased, the volume fraction of the second phase was improved, and the morphology of Mg₃Dy phase changed from fine dots to larger blocks. The addition of the rare earth atom Dy significantly affected the thermal resistance of the alloy. With the increase of Dy content, the thermal resistance of the alloy increased gradually. The thermal resistivity of as-cast Mg-2.3Dy alloy reached the maximum of 26.8×10⁻³ m·K·W⁻¹. With the increase of Dy content, the thermal resistance of the alloy increased gradually. The main reason might be that with the addition of Dy, the dissolved Dy atoms in the alloy matrix and the volume fraction of the second phase increased, which led to the increase of lattice distortion of magnesium matrix. The scattering effect of the crystal lattice on electrons was enhanced and the conduction of the alloy was hindered, which was finally manifested as an increase in the thermal resistance of the alloy. The results showed that the rare earth Dy element was beneficial to improve the thermal resistivity of the alloy, which provided theoretical support and data reference for the design of high thermal resistance magnesium alloy. The following work should continue to study ternary or even multicomponent heat-resistant magnesium alloy, explore the influence of binary phase and multicomponent phase on the microstructure of the alloy and its synergistic effect on the heat resistance performance of the alloy, soas to develop magnesium alloy with good heat resistance performance and realize its application in engineering.