HPMO在大铸锭中的电磁效应及其与凝固组织的关联和调控机制

Defects of coarse grains and macro-segregation always occur in the large casting ingots, which lead to increasing difficulty in subsequent machining processes and unexpected failure of the final products. Refinement is an effective way to solve above problems. Unfortunately, no perfect solution has been figured out so far. The application of Pulse Magneto-Oscillation (PMO) technique in solidifying metal can remarkably refine solidification structure and has been applied in continuous casting process. A new method to control solidification structure of ingots named Hot-top Pulsed Magneto-Oscillation (HPMO) was proposed, which shows the potential to be employed in the mould casting. In the project, both numerical and thermal simulations will be employed to investigate the influence of electromagnetic effects of HPMO generated inside the melt on the solidification process and solidification structure of large ingots with a low cooling rate. Characteristic element and key characteristic parameter will be introduced to characterize the quality of ingots quantitatively, which can take both macrostructure and microstructure into consideration. The electromagnetic effects in large ingots induced by HPMO and its regulation mechanism on solidification structure will be investigated from three scales: macroscopy, midscopy and microscopy. Quantitative relation of parameters of HPMO and key characteristic parameters of ingot will be built. Mechanisms and conditions of grain refinement and homogenization by HPMO in ingot’s casting will be studied. Based on these mechanisms, a scheme would be proposed to improve the solidification structure and solute distribution of large ingots. This research would not only benefit the application of PMO technique to the production of high quality ingot, but also enhance the ability of equipment manufacture and metallurgy industry.

大铸锭凝固组织粗大且不均匀、宏观偏析等缺陷不仅影响其后续加工性能，同时构成最终产品使用中的隐患。细化凝固组织是解决上述问题的有效途径。脉冲磁致振荡凝固细晶技术可以显著细化金属凝固组织，已应用于连铸生产。冒口脉冲磁致振荡技术（简称HPMO）是脉冲磁致振荡应用于模铸生产的新技术，尚处于探索阶段。本项目以HPMO为研究对象，数值模拟和热模拟相结合，研究HPMO在模铸中的电磁效应及其对铸锭凝固过程及组织的影响规律和机制。针对大铸锭研究中宏观尺度与微观组织难以兼顾这一难题，本项目引入“特征单元”的概念并提出“关键特征参数”以解决定量表征难题，从而实现从宏观、介观和微观三个尺度研究HPMO电磁效应与大铸锭凝固组织、溶质分布之间的关联和调控机制，构建HPMO工艺参数与大铸锭关键特征参数之间的定量关系，揭示HPMO改善大铸锭凝固组织、减轻宏观偏析的机制和条件，形成大铸锭均质化调控策略。

大铸锭凝固组织中存在晶粒粗大且不均匀、宏观偏析等缺陷，不仅影响着其后续加工过程中的加工性能，同时构成最终产品使用中的隐患。细化凝固组织是提高金属材料性能和实现凝固组织均质化的有效手段。本项目以冒口脉冲磁致振荡技术（简称HPMO）为研究对象，采用了数值模拟、热模拟和实验研究相结合的方法研究了HPMO作用下大铸锭凝固过程中的电磁效应和凝固组织以及它们之间的关联关系，并提出了大铸锭均质化策略方案。首先，建立了PMO作用下低熔点合金凝固过程中电磁效应分布的数学模型，并结合实验室测量结果，对数学模型进行了修正，提高了数值模拟结果的可靠性。在此基础上，研究了HPMO对大铸锭凝固过程中流场和温度场的影响。其次，运用热模拟技术研究了大铸锭凝固组织特征，确定了大铸锭凝固组织关键特征参数，建立了HPMO工艺参数与关键特征参数之间的数学模型。再次，运用电动力学和凝固理论的知识，揭示了缓冷条件下电磁效应对晶核增殖、枝晶生长、溶质分布的作用机制。工业试验结果表明，HPMO技术可以细化铸锭的凝固组织，减小二次枝晶臂间距，减轻碳偏析程度，改善夹杂物分布。在工业试验结果的基础上探讨了HPMO在大铸锭凝固过程中的电磁效应及其与凝固组织、溶质分布的关联和调控机制，并对HPMO工艺参数进行了优化。通过此项目的研究，进一步丰富了PMO细化金属凝固组织的机理，为HPMO在模铸生产中的广泛应用提供了理论依据。