镁合金挤压铸造多尺度数学模型建立及其计算结果耦合的研究

The squeeze casting is an effective forming method for magnesium alloy in the important industry departments, such as aeronautics, astronautics and weaponry, etc. The research of multi-scale numerical simulation for squeeze casting of magnesium alloy is very valuable to engineering application. In this project, a finite difference-based interface projection level set computational model considering characteristics of liquid metal and gas phase will be developed for gas-liquid two phase mold filling simulation in squeeze casting; a new prediction model considering the variation of thermal parameters and the interaction between the temperature field and the stress field will be set up for squeeze casting defect; adopting the numerical results of temperature and stress field, the numerical simulation works of the microstructure of squeeze cast magnesium alloy will be concluded, which contain the establishment of nucleation model suitable; these proposed models will be evaluated by carrying out numerical simulations and by mold filling experimental data; according to the results of numerical calculation, the process parameters such as pressure, die temperature, pouring temperature and etc. that influence the quality of the casting will be analyzed. Finally, the combination of multi-scale numerical models will be used to display the whole process of squeeze cast. The goal of these works is to provide guidance for the optimization and control of casting technique from both practical application and theoretical analysis.

挤压铸造为镁合金提供了一种有效的成形方法，特别是在航空、航天、兵器等重要工业部门，进行镁合金挤压铸造多尺度数值模拟研究具有十分重要的科学价值。本项目基于挤压铸造特点以及镁合金熔液和空气具有不同的流动特性，建立多相流动Project-Level Set计算模型；考虑温度场和应力场的相互作用关系以及热物性参数随温度、压力的变化规律，建立缺陷预测模型；基于宏观数值模拟中温度场、应力场的计算结果，并考虑瞬态压力作用，针对镁合金密排六方晶体结构，建立微观组织模拟计算模型；最终通过实验对各个计算模型进行验证、校核，并在多尺度模拟计算的基础上，分析挤压压力、模具温度和浇注温度等参数对铸件质量的影响。从而将不同尺度上的计算模型进行有机结合，耦合计算结果，使其成为一个整体，克服各自的局限性，使研究者可从更全局的角度来分析镁合金挤压铸造过程，为镁合金挤压铸造成形和铸件凝固组织控制提供理论和技术的支撑。

在宏观尺度上，建立基于FDM的多相流动计算模型并进行镁合金挤压铸造充型过程数值模拟，建立基于FDM/FEM 的镁合金挤压铸造缺陷预测模型并进行计算；从微观方面对 Mg-Al-RE 合金的中间化合物进行了深入研究，分别针对它们的结合能，形成焓，弹性常数，态密度等进行计算，得到相关数据。开发了金属液态成型过程多尺度模拟软件，为在挤压铸造过程中，分析挤压压力、模具温度和浇注温度等工艺参数对铸件质量的影响打下了基础。针对有限元法难应用于极大网格变形，有限差分法进行自由表面处理困难的问题，本项目在后续的研究中采用SPH方法进行充型过程数值模拟研究，利用SPH气液两相流模型对单个气泡在水中的运动过程进行了模拟，并与实验结果进行了对比，验证了SPH气液两相流模型的正确性，同时也验证了该模型适合处理大密度差的问题，为采用SPH方法进行挤压铸造充型过程气液两相流计算奠定了基础。