基于高数密度基面堆垛层错的高强耐蚀镁合金组织与性能调控机理研究

The poor corrosion resistance (rapid corrosion rate and nonuniform corrosion) and relative low strength are the two inherent characteristics of common magnesium (Mg) alloys. Eliminating these weaknesses is very important for the wide application of Mg alloys. However, at present there are few methods which can improve these two properties simultaneously. Concerning this issue, this project is proposed based on our previous study results. Using the industrial fabrication equipments of Mg alloys but special alloying design and specific process, we achieve a novel microstructure of Mg alloys, i.e. fine-grained “uniform” microstructure based on the formation of profuse basal plane stacking faults (SFs), which opens a new horizon for simultaneous improvement of anti-corrosion and strength of Mg alloys. Centering on the relationship of “preparation-microstructure-property”, firstly the structure of special basal plane SFs are investigated and the formation factors and mechanism are explored in order to realize controllable preparation of Mg alloys with SFs. Secondly, the effects and adjust rules of SFs on the anti-corrosion and strength are studied to optimize the combination of anti-corrosion and strength. Finally, the corrosion and mechanical behavior of Mg alloys with SFs are investigated to reveal the unique effect of SFs and establish the corrosion and strengthening mechanisms based on basal plane SFs, which add the new connotation for the corrosion and strengthening theory of Mg alloys, and also is the reunderstanding of fundamental scientific issues of structural metallic materials.

耐蚀性较差（速率快、局部腐蚀）和强度较低是普通镁合金两个固有弱点，补齐两个“短板”对于推进镁合金广泛应用意义重大，目前少有方法能实现两者同时提高。针对这一问题，本项目利用镁合金工业化生产设备，以特殊合金化设计和制备工艺为技术核心，获得一种全新的微观组织：基于高数密度基面堆垛层错（SFs）形成的细晶“均匀”微观组织，为镁合金耐蚀和强度同时提高打开新视野。围绕“制备-微结构-性能”关系，首先对基面SFs进行细致解析并探明其形成条件和机理，实现高强耐蚀基面SFs镁合金的可控制备。其次，研究基面SFs形成及状态（密度、尺寸等）对合金耐蚀和强度的影响并揭示其调控规律，优化耐蚀和强度的匹配。最后，对基面SFs镁合金腐蚀和力学行为进行研究，揭示基面SFs的独特作用进而建立以基面SFs为核心的低速率均匀腐蚀和强化微观机理，为镁合金耐蚀和强化理论增添新内涵，也是对金属结构材料基本科学问题的再认识和新理解。

传统镁合金两大“短板”，即耐蚀性差（腐蚀速率高和不均匀腐蚀）和强度较低，成为推进轻质镁合金广泛应用的主要阻碍，目前少有方法可以同时补齐两大“短板”。研究表明合金强度和耐蚀性不能良好匹配的核心问题是微观结构不均匀性（即成分和结构不同)导致电位差。因此，获得具有良好强化机制的均匀微观结构是实现镁合金高强和耐蚀兼顾的关键。针对镁合金中的上述科学问题，提出了“均匀电位强化结构”理念，形成了构建“弱阳极纳米间距溶质富集堆垛层错(SESFs)”设计高强耐蚀镁合金新思路，建立了镁合金中SESFs和长周期堆垛有序结构(LPSO)形成精确调控方法，发明了高强耐蚀Mg-RE-Zn合金材料，解决了常规强化相无法同时大幅提高镁合金强度和耐蚀性的难题；发展了纳米尺度微区电位分析技术和原位腐蚀监测技术，揭示了基于SESFs和LPSO独特作用的耐腐蚀和强化机制。特别地，首次通过扫描开尔文探针显微镜在纳米尺度上精确测量了同一合金中弱阳极SESFs和阴极LPSO相的电位差(PD)，并通过实验和理论计算的电子功函数验证了SKPFM测量阳极/阴极性质和PD值的可靠性；首次证明SESFs的优先腐蚀释放大量稀土离子有利于形成有效钝化膜；通过准原位原子力显微镜(AFM)观察发现微观结构中低电位起伏不仅可以有效地降低微电偶腐蚀，还有利于保护膜层的快速形成；此外，还发现添加稀土后形成的Al-Mn-RE化合物更有效捕获杂质Fe，抑制Fe对耐蚀的有害影响。