基于磁致塑性效应变形加工微纳尺度铝基复合材料的机制研究和过程模拟

The in situ nanometer particles reinforced aluminum matrix composites exhibit outstanding comprehensive properties except comparatively low elongation due to the hard reinforced particles. The previous research on the composites subject to the impact of magnetic field has discovered that specific microstructure appeared including high density dislocation, stacking fault and twinning, which showed the characteristics of plastic deformation. It was noted that the magnetic pressure was far below the yield strength of composites, which further implied that the high magnetic field has induced the plastic deformation of materials. Therefore it can be expected that the Magnetoplastic Effect should be beneficial to improve the ability of plastic deformation of materials. In this project synchronic neutron diffraction, edge-cutting high magnetic field, advanced structure detecting techniques and procedural mathematical simulation will be combined to study the strain/stress distribution, structural evolution and plastic deformation process. Most attention will be focused on the influence on the plastic deformation under several conditions as sole external stress field, sole high magnetic field and coupled stress and magnetic fields, plus temperatures, magnetic filed intensity, imposing time and stress status. The inner regularity concerned about magnetic field, electronic spinning, structural evolution, stress distribution, energy emigration and plastic deformation will be explored in detail. Hopefully the relationship between atomic structure, microstructure and macro plasticity will be established. The aim is to develop a flexible solution to improve the ductibility of nanometer particles reinforced aluminum matrix composites together with the enrichment of the Magnetoplastic Effect theory.

原位纳米颗粒增强铝基复合材料具有优异的综合使用性能，但硬质颗粒的存在限制了材料塑性变形能力。前期研究发现复合材料在经过磁脉冲冲击处理时，在磁压强未达到屈服强度时就出现了"高密度位错、层错和孪晶"共存的塑性变形特征，表明强磁场诱发了材料塑性变形，即有望基于"磁致塑性效应"来改善复合材料塑性变形能力。项目研究综合运用中子同步衍射、现代强磁场技术、先进材料结构和组织检测技术并结合过程数值模拟等来研究强磁场处理前后材料中应力应变分布、组织演变及塑性变形过程特征，重点关注单独应力场、单独强磁场、应力场耦合磁场条件以及温度、磁场强度、磁场作用时间和应力状态对塑性变形的影响，探索"磁场作用、电子自旋、组织演变、应力分布、能量变迁和塑性变形"间的内在规律性,在原子结构、微观组织和宏观塑性间建立联系。在丰富完善磁致塑性理论的同时为改善纳米颗粒增强铝基复合材料延展性提供可行方案。

材料电磁加工是新材料发展的重要组成部分，本项目意在通过实验和理论研究探索强磁场对金属材料塑性变形能力的作用效果，即磁致塑性效应。为全面探讨磁致塑性效应在金属材料塑变现象中的普遍规律，项目在原设计铝基复合材料的基础上，又研究了2024Al、7055Al、AZ31Mg和TC4合金中的磁场作用规律。研究结果显示：在磁场静态处理试样中，强磁场能在材料内诱发微塑性变形，主要表现为位错密度提高，在优化参数时材料强韧性同步提高；当结合深冷处理，即在磁场静态深冷处理试样中，织构向着有利于塑变的方向发生转动，材料性能进一步提高。在磁场耦合应力场条件下塑变多种金属型材时，即磁致塑性效应起动态作用时，磁场能促使材料织构转变、晶粒细化、位错分布趋于有序化且密度提高、内部应力分布趋于均匀化，优化参数时材料强韧性同步提高。结合第一性原理研究了有无磁场时材料内电子结构演变规律行为特征，发现有磁场化学键发生了S-T转变，由稳定态变为激发态，导致原子层沿滑移面滑动时更加容易，即塑性提高。实验和理论研究表明：磁致塑性效应可发生在多种金属材料中，可以认为是一种普遍现象。将强磁场应用于金属材料塑性变形过程时可提高合金的塑性变形能力及其他力学性能，是一种行之有效的提高塑变效率和塑变的途径。从微观角度建立的磁致塑性机制填补了该研究方向的空白。