移动横向磁场辅助电弧增材制造技术及凝固组织控制机理

This study is aimed to control solidification microstructure and its defects in GMAW arc additive manufacturing (AAM) process by utilizing travelling transversal magnetic fields (TTMF). By means of experiments combined with theoretical analysis and 3D simulation, the effect of magnetic field on the convection state and its stability, temperature gradient, solute distribution, surface shape and the solidification interface morphology in melt pool are systematically investigated, the heat and solute transport behaviors into mushy zone by the magnetically forced convection are emphatically analyzed. The criterion for columnar-to-equiaxed transition(CET) is established by investigating the resulting dendrite fragmentation and its transport based on side-arm-remelting theory. Based on experimental results, the causal connection between magnetic field pattern, melt pool convection and solidification microstructure is demonstrated, the control mechanism of microstructure and its defects by magnetic field is revealed. This study can not only fill the blank of scientific research on magnetically controlled convection and crystal growth on the GMAW melt pool size scale, enrich the theory for electromagnetic processing of materials, but also provide theoretic basis and technological means for enhancing the service performance of components fabricated by AAM technology.

本项目采用移动横向磁场控制GMAW电弧增材制造凝固组织及其缺陷。采用理论分析、三维模拟和实验测试相结合的方法，系统研究外磁场对熔池对流状态及其稳定性、温度梯度、溶质分布、熔池表面形貌和凝固界面形貌的影响，着重分析磁控对流向糊状区的热和溶质输运行为，并基于晶根重熔理论研究由此引发的枝晶破碎及碎片输运，建立凝固组织由柱状晶向等轴晶转变(CET)的准则；以实验结果为依据，阐明磁场模式、熔池流态和凝固组织三者之间的因果联系，揭示磁场控制电弧增材制造凝固组织及其缺陷的机理。本研究不仅可以填补焊接熔池尺度下的磁场控制熔池对流及晶体生长机理研究的空白，丰富材料电磁加工理论，还为提高电弧增材制造零件整体使役性能提供理论依据和技术手段。

本项目研究利用外加磁场实时作用于电弧增材制造过程以控制凝固组织及其缺陷，结合电磁-流体耦合数值模拟和枝晶破碎理论解释凝固组织的控制机理。主要研究结果包括：成功搭建了横向磁场辅助的电弧增材制造设备原型；建立了无磁场情况下多层堆积增材制造熔池温度和流场计算的三维模型，可以较准确地预测不同工艺参数条件下熔池形状和尺寸，计算误差小于10%；混合使用有限元和有限体积方法构建了三维电磁-流体耦合计算模型，结合实验测试，成功揭示了横向恒定磁场、横向高频磁场对熔池对流和凝固组织的影响规律，发现横向磁场作用使电弧向熔池后方偏转，使熔池发生单向强制对流并驱动熔融金属和热量向熔池后方运动，从而更加直接地冲刷熔池结晶面；开发了基于电弧简化模型的熔池电磁力工程化有限元计算方法；开发了电-磁复合场辅助的电弧增材修复大型壁面方法，实验发现电-磁复合场作用有利于抑制焊接飞溅和气孔形成。在项目计划之外，还开发了基于电弧熔丝增材的铝基复合材料零件的高效低成本制造方法。项目研究为磁场辅助电弧增材制造技术研究提供了基本理论、设备原型、计算模型和一些重要研究结果，实现了电弧增材凝固组织的更优控制。