新型Mg-Al-Ca系镁合金挤压铸造凝固组织演化及其时效固态相变调控机制

面向我国汽车、轨道交通等领域对高性能镁合金的迫切需求，针对传统铸造镁合金中粗大第二相细化调控难、强塑性差瓶颈难题，提出挤压铸造压力下亚快速凝固与时效处理固态相变一体化调控新思路。围绕Mg-Al-Ca系合金挤压铸造压力下亚快速凝固组织调控机制、溶质相界偏聚与第二相细化弥散的协同/竞争机制等关键科学问题，研究合金元素和液、固制备参数对高固溶组织与凝固第二相调控、相界偏聚与析出相/团簇形成和演化的影响规律和作用机制，实现新型Mg-Al-Ca系合金晶粒细化、相界偏聚及第二相弥散分布协同控制。基于细晶、相界偏聚和弥散第二相促进加工硬化、改善室温塑性的策略，建立适合于压力下亚快速凝固Mg-Al-Ca系合金的时效热处理制度，突破“铸造镁合金强塑性同时提高难”的束缚。在理论上的创新：阐明Mg-Al-Ca系合金高强塑性的微合金化效应、微结构尺度效应和界面效应，为发展新型高强塑挤压铸造镁合金提供借鉴。

With the urgent demand of high performance Mg alloys in automobile and track transportation in China, a novel co-regulation fabrication route, i.e., coupling sub-rapid solidification under squeeze casting pressure and solid-state phase transformation during aging treatment, is proposed to solve the bottleneck problems that secondary phase particles in Mg alloys are difficult to be refined and Mg alloys usually suffer from low strength and ductility. Regarding the key scientific problems, i.e., mechanisms for microstructure formation during sub-rapid solidification under squeeze casting pressure, together with synergy/competition relationship between phase boundary segregation of solute atoms and dispersion of secondary phase particles in novel Mg-Al-Ca based alloys, the effects of alloying elements and parameters of liquid-solid co-regulation fabrication on the high solid solution solidification microstructure regulation as well as the evolution of phase boundary segregation and precipitation/cluster will be studied, to synergistically control grain refinement, phase boundary segregation of solute atoms together with dispersed secondary phase particles. Based on the strategy that fine grain structure, phase boundary segregation， together with dispersed secondary phase particles favor enhanced work hardening and ductility at room temperature, the aging treatment regime that is suitable for the novel Mg-Al-Ca based alloys produced by sub-rapid solidification under squeeze casting pressure will be established, to break through the key difficulty, i.e., strength and ductility are hard to achieve simultaneously in cast Mg alloys. The theoretical innovation is to reveal the effects of micro-alloying, microstructural scale and interface on enchanced strength and ductility of Mg-Al-Ca based alloys, which could provide guide for the develeopment of novel high performance squeeze cast Mg alloys.