车用新型低合金超塑性镁合金设计与组织调控机制

面向吉林省汽车支柱产业，针对车用冲压类大面积薄板典型部件“低成本、轻量化、易成型”苛刻需求，提出超塑性镁合金低合金化新思路；围绕新型低合金超塑性镁合金成分设计准则与合金元素交互作用机制、超塑性组织形成与调控机制等关键科学问题，研究低合金中合金元素对液相铸轧凝固组织、异步控轧组织、静态再结晶组织形成与演化影响规律和作用机制，筛选低合金超塑性成分体系，建立低合金体系全流程组织调控新方法。通过研究合金元素对组织热稳定性、室温强韧性和高温超塑性的影响规律和作用机制，揭示低合金体系超塑性变形行为。特色与创新之处在于①通过耦合低合金成分设计和全流程组织调控策略，巧妙实现低合金体系镁合金超塑性组织控制，突破超塑性组织调控难题；②通过晶界析出相特征和溶质偏聚状态调控，提高低合金体系组织热稳定性和高温超塑性能力，突破传统高合金超塑性镁合金的局限。为发展低成本车用新型超塑性镁合金及可控制备新技术提供理论支撑。

Facing the pillar industry of automobiles in Jilin Province, the present project is geared towards the demanding requirements of “low cost, lightweight, and excellent formability” for typical vehicle stamping components made from large-area sheets. With the new concept of low alloying for superplastic Mg alloys, regarding the key scientific problems, i.e. design principles of novel low-alloy superplastic Mg alloys and interaction mechanism between multi- alloying elements, as well as mechanisms for formation and regulation of superplastic microstructure, we sequentially study effects and mechanisms of trace alloying elements on formation and evolution of solidification microstructure during liquid-phase casting and rolling, solid-state microstructure during asynchronous controlled rolling and static recrystallization microstructure, in aiming to screen low-alloy superplastic composition system, and establish a new method for the whole-flow regulation of microstructure in low-alloy system. The superplastic behavior of low-alloy system is also revealed, by systematically studying influences and mechanisms of alloying elements on thermal stability of microstructure, strength and ductility at room temperature together with superplasticity at high temperature. The innovations lie in: (i) through coupling low-alloy composition design and whole-flow microstructure regulation strategy, ingeniously realize the control of superplastic microstructure in low-alloy Mg systems, breaking through the problems of superplastic microstructure regulation, and (ii) by modifying precipitates and segregation solutes at grain boundaries, improve the thermal stability of microstructure and superplasticity at high temperature for low-alloy systems, making breakthroughs in the limitation of conventional high-alloy composition for superplastic Mg alloys. This work could provide theoretical support for the development of low-cost superplastic Mg alloys for vehicles and its controllable preparation technique.