微量元素变质熔体中初生Mg2Si的强迫形核与生长形貌演化及调控机制

This project originating from the great demands for high-performance light alloys in fields of aerospace, automobile and national defense, etc., overcomes the "difficulty in modification design, nucleation regulation and morphology control" that is the key challenges in metallurgy. The project focuses on the critical basic theoretical problems on new high-temperature-resistant magnesium and aluminum alloys, including the heterogeneous nucleation, growth morphology evolution and regulation modification of primary Mg2Si, as well as the interface structure and high temperature strengthening, etc. The innovation of this project lies in the fact that by means of a subtle combination of the first-principle calculations, forced nucleation and regulated modification, primary Mg2Si reinforcement, with features of the thermodynamic stability, a fine size, a regular morphology (i.e. octahedron, cube and sphere, etc.) and stable interface, is formed through modification of active trace element, which solves the major drawback of traditional metallurgical process in which coarse dendrites damage mechanical properties. Based on the new thought of calculating adsorption energy on morphology decision plane, the rule of adorption for modifying elements will be investigated. By regulating and modifying the morphology (crystal face), the interface structure will be controllable. Moreover, the stability of morphology and interface was increased by modificaton, resulting the improvement of high-temperature strength and creep properties. The theoretical innovation of this project includes presenting the criterion of modifying element design, achieving the prediction on modifying effect, revealing the mechanism of forced nucleation of primary Mg2Si in modified melt, clarifying the rule of growth morphology evolution and the mechanism of regulated modification, revealing the high temperature strengthening mechanism of the new modified alloy, and realizing the controllable fabrication of modified alloys, accordingly providing necessary theoretical basis for developments of new high-temperature-resistant light alloys.

本项目面向国家在空天、汽车和国防等领域对高性能轻质合金的迫切需求，突破"变质设计难、形核调控难、形貌控制难"等冶金领域关键难题。针对新型耐高温镁、铝合金中初生Mg2Si非均匀形核、生长演化与调控变质、界面结构与高温强化机制等关键科学问题开展研究。创新思路在于将第一原理计算、强迫形核和调控变质进行巧妙结合，通过微量活性元素变质形成热力学稳定、细小规整（八面体、立方体、球形等）、界面稳定的初生Mg2Si强化相，解决传统冶金中粗大树枝晶损害性能的难题。基于生长决速面吸附能新思路，探索变质元素吸附规律。通过形貌（晶面）调控实现界面结构控制。通过变质提高形貌和界面稳定性，提高高温强度和蠕变性能。在理论上的创新：提出变质元素设计准则，实现变质预测；揭示变质初生Mg2Si强迫形核机理，阐明生长形貌演化规律及调控变质机制；揭示变质合金高温强化机制，实现变质可控制备，为发展新型耐高温变质合金提供理论基础。

本项目针对新型耐高温镁铝合金中初生Mg2Si非均匀形核、生长演化与调控变质、界面结构与高温强化机制等关键科学问题，基于生长决速面吸附能新思路，探索变质元素吸附规律。通过将第一原理计算、强迫形核和调控变质相结合，揭示了吸附-毒化变质元素和吸附-置换变质元素对Mg2Si平衡形貌演化的影响规律，构建了权重总吸附能模型预测初生Mg2Si的变质效果；揭示了不同变质元素类型、含量条件下初生Mg2Si强迫形核机理；阐明了变质条件下不同三维形貌的生长过程和形貌演化规律；给出了变质Mg2Si与基体的界面微结构特征；揭示了初生Mg2Si形貌、尺寸和数量对Al-Mg-Si合金力学性能影响的共性规律，实现变质可控制备，为发展高性能变质轻合金提供理论基础。