Phase equilibria of Mg-La-Zr system and thermal conductivity of selected alloys

• Published in: Journal of alloys and compounds Vol. 731; pp. 784 - 795
• Main Authors: Zhu, Wen-Fei, Luo, Qun, Zhang, Jie-Yu, Li, Qian
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.01.2018; Elsevier BV
• Subjects: Alloy systems; Alloys; Binary systems; Constitution; Electron microscopy; Grain boundaries; Heat conductivity; Heat transfer; Heat transmission; Intermetallic compound; Magnesium base alloys; Mechanical properties; Mg-La-Zr system; Microstructure; Peritectic reactions; Phase equilibria; Thermal conductivity; X ray spectrometers; X-ray diffraction; Zirconium; Phase equilibria; Thermal conductivity; Mg-La-Zr system; Intermetallic compound
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.10.013

The investigation on phase equilibria of Mg-La-Zr system contributes to finding the alloy composition with good mechanical properties and superior thermal conductivity along with the variation of phase constitution and microstructure. In our study, four key Mg-La alloys were used to investigate the phase equilibria of Mg-La binary system via a combination of X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS). Two peritectic reactions have been found among the composition of 50.0–75.0 at.% Mg. It is determined that LaMg2 is a stable phase below 500 °C, while La5Mg41 is not stable in Mg-La system. The phase equilibria of Mg-La-Zr were investigated through one diffusion couple of Mg/La84.6Zr15.4 and three Mg-La-Zr alloys. The thermodynamic description of the Mg-La-Zr system was assessed at 300–500 °C. By the calculation of equilibrium solidification of Mg-La-Zr alloys, it is predicted that with the increase of La content, eutectic regions composed of LaMg12 and magnesium phase present a dense network in grain boundary of primary hcp(Mg) which hinder the heat transmission. Mg99.7La0.2Zr0.1 (136.6 W/(m·K)) exhibits higher thermal conductivity than Mg99.1La0.8Zr0.1 (113.9 W/(m·K)). [Display omitted] •Evidences for phase equilibria in Mg-La system and Mg-La-Zr system were obtained.•Thermodynamic description for Mg-La-Zr in Mg-rich region was obtained.•Eutectic regions composed of LaMg12 and Mg can hinder heat transmission.