Mg-RE(La, Ce, Nd)-Zn合金中析出相对热导率的影响机理

Magnesium alloy is the lightest metal structural material, but the low thermal conductivity and poor high temperature strength restrict its application. The root of problem is that the solid solution elements, precipitate phases and the interfaces between precipitate phase and matrix decrease the electronic thermal conductivity, which limits the heat dissipation performance of magnesium alloys. This proposal plans to reveal the influence principle of alloying elements on the thermal conductivity through calculating the electron density of state of α-Mg with rare earth elements (RE=La, Ce, Nd) solid solution and Mg-RE-Zn precipitate phases coupled with experimentally measuring the thermal conductivity of alloys. Thereby, the alloying elements and precipitate phases which lead to high thermal conductivity can be provided. In order to obtain the objective precipitate phases, the thermodynamic description of Mg-RE-Zn system optimized through CALPHAD method is used to predict the precipitate phase formation temperature, composition range and solidification path, etc. The phase transition sequence and the relationship of precipitate phase content vs. temperature and time are determined by high-resolution transmission electron microscope and high temperature in-situ X-ray diffraction. Based on that, the thermodynamic and kinetic mechanisms of formation and transformation of precipitate phases can be revealed, which directs to the design of alloy composition and heat treatment temperature. The proposed principle and revealed mechanism would be the scientific basis for developing high heat dissipation magnesium alloys.

镁合金是目前最轻的金属结构材料，但其热导率低、高温强度不足等问题严重制约了它的应用，根源是固溶元素、析出相及其与基体的界面使电子热导降低，从而限制了镁合金的散热性能。本项目拟通过第一性原理计算含有稀土元素固溶的α-Mg和Mg-RE(La, Ce, Nd)-Zn析出相的电子态密度，结合实验测定热导率，揭示合金元素对镁合金热导的影响规律，给出具有较高热导率的合金元素种类和析出相类型。通过CALPHAD方法优化Mg-RE-Zn体系热力学描述，预测这些析出相的形成温度、成分范围、凝固路径等，利用高分辨透射电镜、高温原位X射线衍射测定析出相在热处理过程中的相转变次序和析出相含量与温度、时间等因素的关系，阐明析出相形成与转变的热力学机制和动力学机理，从而指导合金成分和热处理温度设计，为开发高散热性能镁稀土合金提供科学依据。

镁合金热导率低、高温强度不足等问题严重制约了它在汽车、民用等领域的应用，其根源是合金固溶、第二相、析出相及其与基体的界面使电子热导降低，从而限制了镁合金的散热性能。本项目结合实验和计算方法揭示RE(La,Ce,Nd)和Zn合金元素对镁合金热导的影响规律，构建Mg-RE-Zn体系热力学和热导率数据库，设计开发了高导热Mg-Zn-La/Ce合金，为开发高散热性能镁稀土合金提供科学依据。.① 实验探究了不同第二相（REMg12和τ1-RE0.077(Mg, Zn)0.923）、不同第二相含量、Zn固溶量、析出相种类（β1’和β2’）和形貌特征对热导率的影响规律。REMg12对热导率的影响更小，但τ1更利于提高强度。RE元素的添加降低了Zn在基体中的固溶度，提高了合金热导。析出相β1’降低了基体中Zn和RE元素固溶，同时提高了热导和强度。.② 通过CALPHAD方法优化Mg-RE-Zn体系热力学描述，提出了热导率计算方法，构建了Mg-RE-Zn体系热导率数据，设计了高导热铸造镁合金，铸态Mg97.4-99.4Zn1.5-2.4La0.2-0.6和Mg97.7-98.3Zn1.6-2.0Ce0.1-0.5合金的热导率> 120 W/(m·K)，屈服强度> 85 MPa。.③ 利用高分辨透射电镜测定析出相在热处理过程中的相转变次序和析出相含量与温度、时间等因素的关系，阐明析出相形成与转变的动力学机理，揭示析出过程中热导率和强度随析出过程的变化规律，开发了兼具高导热和高强度的镁合金，时效处理后Mg97.3Zn2.6La0.1和Mg97.4Zn2.5Ce0.1合金热导率和屈服强度分别为155.3 W/(m·K)，172.1 MPa和148.4 W/(m·K)，172.9 MPa。