稀土/碱土元素在Mg-Zn合金中的协同合金化效应及其强化机制研究

The collaborative addition of rare earth (RE)/ alkaline earth (AE) plays a significant role on the improvement of mechanical properties of wrought Mg–Zn alloy, the systematic investigation of the strengthening mechanism of RE/AE collaborative alloying in Mg–Zn alloy, will contribute to the design and industrial application of wrought Mg–RE alloy with superior mechanical properties. In the current study, the low-cost Ce/La mischmetal (without Pr and Nd) and Ca, will be selected as RE and AE element, respectively, the effect of Ce/La, Ca contents and their existence on the microstructural and texture evolution of Mg–Zn alloy during the hot extrusion process and ageing treatment will be systematically investigated, and the collaborative influence mechanism of Ce/La and Ca on the dynamic recrystallization behavior and ageing-hardening response will be clarified. On the basis above, the influence of Ce/La and Ca contents on the mechanical properties of the as-extruded Mg–Zn alloys will be investigated, the chemical composition, extrusion and heat treatment conditions will be optimized to process a high-strength Mg–Zn–Ca–Ce/La alloy and achieve sufficient improvement, and the strengthening model and the corresponding mechanism will be clarified. The research work will provide the theoretical guidance for the collaborative alloying of new low-cost wrought Mg alloys with superior properties, and give rise to a new way to achieve the balance of rare earth resource utilization in China.

稀土/碱土元素的协同加入对变形Mg–Zn合金力学性能的改善有着积极的作用，系统研究稀土/碱土协同合金化在Mg–Zn合金中的强化机制，对高性能稀土镁合金的设计和工业应用具有积极的意义。本项目拟选用提取Pr、Nd后剩余的、成本较低的Ce/La和Ca作为稀土和碱土元素的代表，系统地研究Ce/La和Ca元素含量及存在形式对Mg–Zn合金热挤压和时效处理过程中组织和织构演化的影响规律，阐明Ce/La与Ca元素之间的协同作用对合金动态再结晶行为和时效硬化效应的影响机制；在此基础上，研究Ce/La和Ca元素含量与Mg–Zn合金力学性能的关联性，通过优化成分设计、挤压及热处理工艺，突破现有合金的强度瓶颈，制备出高强度的Mg–Zn–Ca–Ce/La合金，建立强化模型并揭示其强化机理。本项目的研究成果将为新型低成本高性能变形镁合金的协同合金化提供理论指导，并为促进我国稀土资源的平衡利用提供一种新的途径。

稀土/碱土元素的协同合金化对于变形Mg-Zn合金力学性能的改善具有极其重要的作用，对于未来高性能镁合金的设计与开发具有积极的意义。然而，目前对于其强韧化机理方面还缺乏系统的研究，本项目采用提取Pr、Nd后剩余的、低成本的Ce/La混合稀土与Ca元素为代表，通过对比单一的Ca、Ce/La元素添加，系统地研究了Ca与Ce/La元素的协同合金化效应对挤压态Mg-Zn合金显微组织、织构演化与力学性能的影响规律，证明了协同合金化导致传统的Ca2Mg6Zn3相显著细化，有效地限制了合金在热变形过程中再结晶晶粒的生长，实现了最有效的晶粒细化效应；协同合金化在一定程度上弱化了Mg-Zn合金中传统的基面丝织构，但对主要织构类型的较小；协同合金化导致第二相/析出相的细化，显著增强了合金的弥散/析出强化效应，与晶界强化效应共同作用，极大地提高了Mg-Zn合金的力学性能，实现了变形Mg-Zn合金的强韧化；建立了合理的变形镁合金强化模型，并阐明了相关的强化机制。