【作者】 赵静蕊；

【导师】 杜勇； 张利军；

【作者基本信息】 中南大学 ， 材料科学与工程， 2013， 博士

【摘要】 材料的热力学信息是进行材料动力学计算及微观组织演变模拟的基础,因此CALPHAD (CALculation of PHAse Diagram)技术在材料的设计与开发中发挥着越来越重要的作用。Cu、Fe、Mg、Mn、Si是多元商业铝合金中的主要合金或杂质元素。为了设计并开发新—代高性能铝合金,必须建立精确的热力学数据库。本论文针对商业铝合金中的重要体系Al-Cu-Fe-Mg-Mn-Si展开研究,力求为多组元铝合金的应用开发提供可靠的热力学描述。本工作的主要思路是：首先,基于已经发表的相关二元体系的热力学描述,利用本工作的实验结果,并结合文献数据,分别对Cu-Fe-Si、Cu-Mg-Si、Fe-Mg-Si、Cu-Fe-Mg三元系进行热力学计算,得到一套可以合理描述Cu-Fe-Mg-Si体系的热力学参数；之后,结合本研究室已完成的其它相关二元系、三元系、四元系的热力学参数,构建Al-Cu-Fe-Mg-Mn-Si六元系热力学数据库。最后,利用该数据库对商业铝合金的重要体系进行热力学计算,并用希尔凝固模型预测一系列商业铝合金在凝固过程中的相变序列。本工作取得的主要成果由以下六部分组成：(1)在对文献报道的相图和热力学数据严格评估的基础上,综合利用X射线分析法(XRD)、扫描电镜(SEM/EDX)、电子探针显微分析(EPMA)和差热分析(DTA)对Cu-Fe-Si体系整个成分范围内的相平衡关系进行了研究。测定了Cu-Fe-Si体系在750℃的等温截面,获得了该体系在30和70at.%Cu的垂直截面上的相转变温度。基于本次实验结果,并结合文献数据,对Cu-Fe-Si体系进行了热力学优化计算,得到了该体系一套比文献报道更为合理的热力学参数。此外,将所获得的热力学参数应用到对抑制钢铁“表面裂纹”的合金元素选择和“核-壳材料”的形成成分范围预测中。本工作中还对三元体系的液相溶解度间隙的形成判据进行了详细分析及归纳。(2)通过粉末冶金方法制备了Cu-Mg-Si三元合金样品,利用X射线分析法测定了该三元系在500℃和700℃的相关系,并证明了三元化合物Sigma (Cu16Mg6Si7)、Tau (Cu3Mg2Si)和Laves_C15((Cu0.8Si0.2)2(Mg0.88Cu0.12))相的存在。通过严格评估文献中的相图和热力学性质数据,并结合本次实验结果,对Cu-Mg-Si体系进行了热力学优化计算,成功地对有复杂相关系的Laves相进行了热力学模拟。(3)在对文献中Fe-Mg-Si体系的相图数据和热力学数据进行严格评估的基础上,对该体系进行热力学优化,得到了一套可以合理描述该体系实验数据的热力学参数。基于所获得的热力学参数构筑了Fe-Mg-Si体系的液相面投影图和反应图,并详细描述了在富Mg端和富Fe端的液相溶解度隙的复杂零变量反应。(4)采用粉末冶金方法测定了Cu-Fe-Mg三元系在室温、500和700℃的相关系。该体系中未发现三元化合物。通过热力学外推的方法,得到该三元系的热力学参数,并对该体系在室温、500和700℃的等温截面进行计算。计算结果与实验结果对比表明利用热力学外推方法就可以很好地描述该体系。利用外推的结果,本工作还预测了Cu-Fe-Mg体系一系列的等温截面和关键的垂直截面,并构筑了Cu-Fe-Mg体系完整的液相面投影图与反应图。(5)将上述工作得到的Cu-Fe-Si、Cu-Mg-Si、Fe-Mg-Si、Cu-Fe-Mg体系的热力学参数与本研究室已完成的其它相关二元系、三元系及四元系参数相结合,建立了Al-Cu-Fe-Mg-Mn-Si六元系热力学数据库。基于所建立的六元系数据库,本工作对Al-Cu-Mg-Mn、Al-Cu-Fe-Mg、 Al-Cu-Fe-Si、Al-Cu-Mg-Si、Al-Fe-Mg-Si四元系和Al-Cu-Fe-Mg-Si、 Al-Cu-Fe-Mg-Mn五元系进行了热力学计算,得到了以上所有体系富Al角含液相的零变量反应温度和成分,并绘制了Al-Cu-Mg-Mn、 Al-Cu-Fe-Mg、Al-Cu-Fe-Si、Al-Cu-Mg-Si、Al-Fe-Mg-Si四元系在富Al角的液相面投影图。计算结果与文献数据取得了良好的一致性。此外,本工作还计算了Al-Cu-Fe-Mg-Si五元系在Al-Cu、Al-Si、Al-Mg边界的液相面投影图,以及Al-Cu-Fe-Mg-Mn五元系在Al-Cu、AI-Mg、 Al-Mn边界的液相面投影图。(6)在本工作建立的Al-Cu-Fe-Mg-Mn-Si六元系热力学数据库的基础上,采用杠杆定律和Scheil模型对Al-Cu、Al-Mg、Al-Si系列的17个商业铝合金的凝固过程进行了平衡和非平衡凝固计算。所计算的凝固曲线能够可靠地预测文献中的实验结果。更多还原

【Abstract】 The phase diagram and thermodynamic information of materials is the basis for kinetic and even microstructure evolution simulation. Cu, Fe, Mg, Mn and Si are the main alloying elements or impurity elements in commercial aluminum alloys. In order to improve the properties of the current Al alloys or even design novel high-performance Al alloys, establishment of a precise thermodynamic database including Al, Cu, Fe, Mg, Mn, Si is the prerequisite.The overall idea of this thesis is as follows:First, based on well-established thermodynamic descriptions of the constituent binary systems, as well as the experimental data of the ternary systems obtained in the present work and available in the literature, thermodynamic parameters for the four constituent ternary systems, i.e., Cu-Fe-Si, Cu-Mg-Si, Fe-Mg-Si and Cu-Fe-Mg, were optimized using the CALPHAD method, from which the Cu-Fe-Mg-Si thermodynamic database can be preliminarily obtained. After that, the Cu-Fe-Mg-Si thermodynamic database was combined with thermodynamic parameters of other relevant binary, ternary and quaternary systems published in our research group to establish the Al-Cu-Fe-Mg-Mn-Si thermodynamic database. Later, based on this6-component thermodynamic database, phase diagram calculations in a series of important systems in commercial aluminum alloys was conducted and compared with the experimental data. Finally, the phase transition sequence in a series of commercial aluminum alloys during solidification was predicted using Scheil-Gulliver model.The main work in this thesis consists of six parts and is concisely described in the following:(1) Based on a critical assessment of the literature data, the phase equilibria of the Cu-Fe-Si system over the whole composition range was investigated by using a combination of X-ray analysis (XRD), scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDX), electro probe microanalysis (EPMA) and differential thermal analysis (DTA). The isothermal section at750℃of the Cu-Fe-Si system was determined, and new phase transition temperatures along vertical sections at30and70at.%Cu were measured. A thermodynamic modeling for the Cu-Fe-Si system was then conducted by considering the reliable experimental data from the literature and the present work. A set of self-consistent thermodynamic parameters which is found to be more reasonable than the previous assessments was obtained. The assessed thermodynamic parameters were also successfully applied to two technical cases in material design:the selection of alloying elements for the control of the formation of surface fissures in iron, and the prediction of the formation of Core/Shell type alloys. The criterion for the formation of the liquid miscibility gap in the ternary system was also summarized in this work.(2)13ternary Cu-Mg-Si alloys system were prepared by means of the powder metallurgy method. Phase equilibria at500and700℃of Cu-Mg-Si system were determined using XRD analysis. The existence of3ternary compounds in this system was verified:Sigma (Cu16Mg6Si7), Tau (Cu3Mg2Si) and Laves_C15((Cu0.8Si0.2)2(Mg0.88Cu0.12)). A thermodynamic modeling for the Cu-Mg-Si system was conducted on the basis of the experimental data obtained in this work and those critically reviewed from the literature. The complex phase relationship between Laves phase and other phases has been successfully modeled in this work. In addition, most of the experimental data can be reproduced by the presently obtained thermodynamic parameters.(3) All of the phase diagram and thermodynamic data of the Fe-Mg-Si system available in the literature were critically reviewed and assessed using thermodynamic models for the Gibbs energies of individual phases. A set of self-consistent thermodynamic description for the Fe-Mg-Si system was thus obtained. The liquidus projection and reaction scheme for the entire Fe-Mg-Si system are calculated using the thermodynamic parameters obtained in this work. The monotectic invariant equilibira related to the liquid miscibility gap in the Fe-rich corner and Mg-rich corner is also described in detail.(4) The phase equilibria of Cu-Fe-Mg system at room temperature,500℃and700℃were determined with powder metallurgy method. No ternary compound was observed in this ternary system. The thermodynamic description of the Cu-Fe-Mg ternary system was obtained via direct extrapolation from the three boundary binary Cu-Fe, Cu-Mg and Fe-Mg systems. The calculated isothermal sections at room temperature,500℃and700℃are consistent with the experimental results, indicating that there is no need to introduce any ternary interactive parameters. A series of isothermal sections and several typical vertical sections were then model-predicted. The projection of the liquidus surface and the reaction scheme were also constructed.(5) The thermodynamic parameters obtained in the above ternary systems were combined with those in other constituent binary, ternary and quaternary systems published in our research group to establish a thermodynamic database for the Al-Cu-Fe-Mg-Mn-Si system. Based on this newly established Al-Cu-Fe-Mg-Mn-Si thermodynamic database, thermodynamic calculations were performed in the Al-Cu-Mg-Mn, Al-Cu-Fe-Mg, Al-Cu-Fe-Si, Al-Cu-Mg-Si, Al-Fe-Mg-Si quaternary systems and the Al-Cu-Fe-Mg-Si, Al-Cu-Fe-Mg-Mn quinary systems. The temperatures and compositions of liquidus invariant reactions in Al-rich corner for all the above systems were calculated and compared with the experimental data. The liquidus surfaces in Al-rich corner for Al-Cu-Mg-Mn, Al-Cu-Fe-Mg, Al-Cu-Fe-Si, Al-Cu-Mg-Si and Al-Fe-Mg-Si quaternary systems were constructed. The calculated results are in good agreement with the literature data. The liquidus surfaces for the Al-Cu-Fe-Mg-Si quinary system in Al-Cu, Al-Si and Al-Mg sides, as well as those for Al-Cu-Fe-Mg-Mn quinary system in Al-Cu, Al-Mg, Al-Mn side, were also presented.(6) The thermodynamic description for Al-Cu-Fe-Mg-Mn-Si system was then employed to analyze the phase transition sequence of17commercial aluminum alloys of Al-Cu, Al-Mg and Al-Si series during solidification. Solidification paths of those aluminum alloys were simulated using the lever rule and the Scheil-Gulliver model. The simulation provides a good prediction for the experimental data available in the literature.更多还原