基于非平衡凝固与固态相变一体化的高强韧铸造铝合金设计

Aluminum casting alloys are a type of important engineering materials. Strengthening and toughening of these alloys are important issues in this field. The processing of the aluminum casting alloys normally involves non-equilibrium solidification and the subsequent solid state transformation. The former inevitably influences the latter and the final microstructures/properties. Unfortunately, this issue has not been paid enough attention. This project will focus on the Al-Si-Mg type aluminum casting alloy. Firstly, the formation, evolution, and strengthening and toughening mechanisms of the alloys subjected to the united non-equilibrium solidification and solid-state treatment (UNSST) will be illuminated by systematic experiments. Then, based on the idea of united non-equilibrium solidification and solid-state transformation, a theoretical microstructure prediction model correlating alloy composition, driving force and barrier (or activation energy) for solidification and multiple-stage solid-state transformation and parameters used to characterizing microstructures of the alloys will be established. Furthermore, the key factors and mechanisms of deformation and deformation induced strengthening and toughening of the UNSST processed alloys will be elucidated by experiments, and the influences of deformation on thermodynamics and kinetics of phase transformation will be combined into the microstructure prediction model. In the end, in terms of the phenomenological relationship between microstructures and mechanical properties, the target microstructure aiming to significantly improve strength and toughness of the aluminum casting alloys will be designed. By combing the calculations by means of the established microstructure prediction model and the limited-scale experiments, the alloy composition and the key processing parameters fulfilling the as-designed target microstructure will be achieved. This project may not only provide a new way in designing compositions and processing parameters of high strength high toughness aluminum casting alloys, but also contribute to development of the theories of solidification and solid state transformation.

铸造铝合金是重要的工程材料，强韧化是该类合金的重要研究课题。此类合金的制备加工涉及非平衡凝固及后续固态相变，前者不可避免影响后者及最终组织/性能，但并未得到应有重视。本项目拟聚焦Al-Si-Mg系铸造铝合金，首先，通过实验，揭示合金非平衡凝固与固态相变共同作用下多级组织的形成、演化及强韧化机制；进而，基于非平衡凝固与固态相变一体化的思想，针对合金制备加工经历的凝固及多阶段固态相变，利用相变建模的方法，建立耦合成分、各阶段相变热/动力学参数及微观组织特征参量的一体化组织预测模型；进一步，通过实验，阐明一体化处理合金变形及形变强化控制因素及作用机理，并将变形因素引入组织预测模型；最终，基于组织与性能间唯象关系设计目标组织，通过模型计算结合有限成分及工艺范围内扩展性实验，获得大幅提升合金强韧性的成分及加工工艺。本项目将为高强韧铸造铝合金的研发提供新思路，也将对凝固及固态相变理论发展产生重要贡献。

铸造铝合金是重要的工程材料，强韧化是该类合金的重要研究课题。本项目聚焦Al-Si-Mg系铸造铝合金，通过实验，揭示了合金非平衡凝固与固态相变共同作用下多级组织的形成、演化及强韧化机制；基于非平衡凝固与固态相变一体化的思想，建立了耦合成分、各阶段相变热/动力学参数及微观组织特征参量的一体化组织预测模型；进一步，将变形因素引入组织调控，研究了形变热处理对Al-Si-Mg系铸造合金强化及加工硬化的影响；最终，获得了大幅提升合金强韧性的成分及加工工艺。本项目取得了以下主要学术成果：（1）建立了铸造铝合金非平衡凝固与固态相变一体化模型，描述了铸造铝合金凝固、固溶、时效全流程组织演化过程；（2）提出了Al-Si-Mg铸造合金的非平衡凝固与固态相变一体化的处理思路，大幅度提高了材料的固溶和时效效率，同时提高了材料的强度和塑性；（3）揭示了激光选区重熔条件下，铸造Al-Si-Mg合金的强化及加工硬化机理，发现该非平衡凝固条件下合金独特的胞状组织产生了强背应力，进而对合金的强化及加工硬化产生显著影响。以上成果Acta Materialia、Journal of Alloys and Compounds等期刊发表SCI论文11篇，申报国家发明专利1项，获2019年度教育部自然科学一等奖1项。研究成果对铸造合金设计、组织调控及热处理工艺设计具有重要的指导意义。