新型多元少量镁合金准快速凝固行为与过饱和凝固组织控制

This project focuses on the bottleneck problem of “severe composition segregation and coarse primary and eutectic phases” in conventional casting structure of traditional high-alloy Mg systems. By subtle combination of the composition design ideas of multiple and small amounts of element alloyings, as well as the near-rapid solidification process (100-1000K/s), we obtain the supersaturated solid solution with high contents of alloying elements. The project concentrates on the critical theoretical problems in regard to the effects of alloying elements on the near-rapid solidification behavior of Mg alloys, and the formation mechanism of supersaturated microstructure with high solid solution contents. By investigating the influences of alloy composition and cooling rate on the solidification interval of Mg alloys, distribution and segregation behavior of solute atoms, as well as the evolution of eutectic phases and dendrites, we aim to optimize the composition of new type of near-rapid solidification Mg alloys and realize the controllable preparation of supersaturated structure. The theoretical innovation of this project includes ① clarifying the dynamic laws of near-rapid solidification behavior based on the composition design ideas of multiple element alloyings with small amounts, realizing the control of solute distribution and segregation, which solves the major drawback in severe composition segregation in traditional high-alloy Mg; ② revealing the formation mechanism of supersaturated solid solution, achieving the homogenization of solidification structure and grain refining, which overcomes the constraint of difficulties in fully dissolving the traditional coarse eutectic phases. The results can provide theoretical support for short-flow manufacturing of Mg alloys with high performance.

本项目面向传统高合金镁体系常规铸造组织“成分偏析严重、初生和共晶相粗大”瓶颈问题，巧妙将多元少量成分设计思路和准快速凝固（100-1000K/s）相结合，获得合金元素高含量过饱和固溶。重点针对合金元素作用下镁合金准快速凝固行为、高固溶过饱和组织形成机制等关键科学问题开展研究，通过探索合金成分和冷却速度对镁合金凝固区间、溶质分布与偏析以及对共晶相和枝晶演化的影响，优化新型准快速凝固镁合金成分，实现过饱和组织可控制备。特色与创新之处为①从多元少量成分设计出发，阐明准快速凝固行为动力学规律，实现溶质分布和偏析控制，突破传统高合金镁成分偏析严重的束缚；②揭示过饱和组织形成机制，实现凝固组织均匀化和晶粒细化，突破传统粗大共晶相难以充分固溶的束缚。为高性能镁合金短流程制造提供理论支撑。

准快速凝固（冷却速率：100-1000 K/s）是解决铸造镁合金组织粗大、偏析问题的理想选择之一。遗憾的是，目前有关准快速凝固镁合金成分体系的研究较少，其非平衡凝固组织控制难。本项目针对合金元素作用下镁合金准快速凝固行为、高固溶过饱和组织形成机制等关键科学问题，从多元少量成分设计出发，系统研究了合金元素与准快速凝固高冷却速率对溶质分布规律、凝固组织演化的影响规律。阐明了准快速凝固高冷却速率可扩展合金元素在镁基体中固溶程度，显著缓解枝晶间偏析行为；发现了由于多元溶质的交互作用，不同类型合金元素微观偏析的改善程度不同新现象；揭示出准快速凝固多元镁合金初生alpha-Mg枝晶和共晶相的演化规律和协同细化机制；建立了过饱和固溶组织特征与力学性能的定性关系，开发出适合准快速凝固的新型多元Mg-Al-Zn-Sn合金成分体系，为实现高性能镁合金短流程产业制备提供了理论基础。

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