【作者】 向浩亮；

【导师】 刘华山；

【作者基本信息】 中南大学 ， 材料科学与工程， 2023， 硕士

【摘要】 镁合金具有低密度、高的比强度和比刚度、良好的导热性能和减震性能,被广泛应用于3C产品、汽车工业和航空航天等方面。研究表明,在Mg-Gd-Y系列合金中添加Ag元素能够促进第二相的析出,缩短时效时间,提高析出相的体积分数的作用;添加稀土Er元素可以进一步细化合金的晶粒。然而,其中含Ag和含Er的Mg-Y三元系相图鲜有研究,这使得该系列合金的成分优化以及新成分合金的开发缺乏理论指导。为了给该系列镁合金开发和成分优化提供可靠的参考,对相关体系的镁合金相图进行研究是十分必要的。本工作采用平衡合金法分别对Mg-Y-Ag和Mg-Y-Er三元系进行实验研究,并对两个体系进行热力学建模。其主要的工作内容有:（1）采用电子探针显微分析（EPMA）和X-ray衍射（XRD）等实验方法,研究了Mg-Y-Ag体系在400℃和500℃下的等温截面。在400℃和500℃的等温截面中分别确定有24个和14个三相区。该三元系在400℃时存在四个新的三元化合物τ₁、τ₂、τ₃和τ₄,但在500℃下,这四个化合物均不能稳定存在。通过DSC和纳米压恒实验确定了四个新相的熔点和杨氏模量。这两个等温截面都探测到了已经报道的三个三元化合物Mg Ag Y、Mg Ag₂Y和Mg₃Ag₁₀Y₄。另外,Ag元素在Mg₂Y相中溶解度可达12.84 at%,而且,Mg-Y二元中间相Mg₂₄Y₅和Mg Y均表现出了很大第三组元固溶度。（2）实测了Mg-Y-Er三元系400℃和500℃下富镁端的等温截面。结果表明,两个等温截面中Mg₂₄Y₅和Mg₂₄Er₅、Mg₂Y和Mg₂Er、Mg Y和Mg Er均形成连续固溶体。实验中并未发现文献中以第一性原理计算预测的Mg₂YEr相。除此之外,本工作测定了第三组元在Mg-Y和Mg-Er体系中二元中间相的固溶度范围。（3）基于本工作实测的相平衡关系、文献报道的相关相图和热力学信息,采用CALPHAD方法进一步计算优化了Mg-Y-Ag和Mg-Y-Er两个三元系,得到了一套合理自洽的热力学参数,并建立了Mg-Y-Ag-Er热力学数据库。其中,部分亚点阵模型中的端际相的形成焓采用了第一性原理计算的结果。在此基础上,采用Scheil凝固模型模拟了Mg-Y-Ag和Mg-Y-Er中典型合金的凝固路径,这与典型合金的凝固组织形态与形成过程相吻合。图64幅,表25个,参考文献165篇更多还原

【Abstract】 Magnesium alloys are widely utilized in the automobile sector,3C goods,and aerospace due to its low density,high specific strength and specific stiffness,strong heat conductivity,and vibration damping qualities.According to research,the addition of Ag elements in Mg-Gd-Y series alloys may decrease the aging time,enhance precipitation,and raise the effect of volume fraction of precipitated phase,while the addition of rare earth Er elements can further purify the alloy’s grains.However,there is little research on the phase diagram of the Mg-Y ternary system containing Ag and Er,which makes the composition optimization of this series of alloys and the development of new composition alloys lack theoretical guidance.In order to provide a reliable reference for the development and composition optimization of this series of magnesium alloys,it is necessary to study the phase diagrams of magnesium alloys of relevant systems.In this work,the Mg-Y-Ag and Mg-Y-Er ternary systems were investigated experimentally using the equilibrium alloy method and thermodynamic modeling was performed for both systems,respectively.Following are the primary contents of the work:（1）The isothermal sections of the Mg-Y-Ag system at 400°C and500°C were investigated using experimental methods such as electron probe microanalysis（EPMA）and X-ray diffraction（XRD）.Twenty-four and fourteen three-phase regions were identified in the isothermal sections at 400°C and 500°C,respectively.Four new ternary compoundsτ₁,τ₂,τ₃,andτ₄,existed in this ternary system at 400°C,but none of these four compounds could be stabilized at 500°C.The melting points and Young’s moduli of the four new phases were determined by DSC and Nano-indentation experiments.The three reported ternary compounds Mg Ag Y,Mg Ag₂Y,and Mg₃Ag₁₀Y₄ were detected in both isothermal sections.In addition,the elemental Ag solubility in the Mg₂Y phase could reach 12.84at%,and both the Mg-Y binary intermediate phases Mg₂₄Y₅ and Mg Y exhibited a large third group solid solubility.（2）The isothermal sections of the Mg-Y-Er ternary system at 400°C and 500°C at the Mg-rich end were measured.The results show that Mg₂₄Y₅ and Mg₂₄Er₅,Mg₂Y and Mg₂Er,Mg Y and Mg Er form continuous solid solution in both isothermal sections.The Mg₂YEr phase predicted by the first-principle calculations in the literature was not found in the experiments.Furthermore,the third group of elements’range of solid solubility in the binary intermediate phases of the Mg-Y and Mg-Er systems was determined in the current research.（3）Based on the phase equilibrium relationship measured in this work and the relevant phase diagram and thermodynamic information reported in the literature,the two ternary systems of Mg-Y-Ag and Mg-Y-Er were further calculated and optimized by using the CALPHAD method to obtain a set of reasonable thermodynamic parameters and establish the Mg-Y-Ag-Er thermodynamic database.Among them,the formation enthalpy of the terminal phase in some sublattice models were calculated by the first principle.On this basis,the solidification path of typical alloys in Mg-Y-Ag and Mg-Y-Er were simulated using the Scheil solidification model,which were consistent with the solidification structure and formation process of typical alloys.更多还原