新型高强度BCC结构Mg-11Li-xAl/Zn合金的腐蚀损伤机制及表面膜研究

Mg-Li alloy is the lightest weight and ideal structural-metallic-material, whereas the low absolute mechanical strength and poor corrosion resistance are always the bottleneck problems for its development and application. Based on the body-centered cubic (BCC) structured Mg-Li-Al/Zn alloys strengthened by solution treatment, this project will be carried out to confirm the optimal composition of Al/Zn and the solution treatment process, meanwhile the static corrosion, stress corrosion and surface films of the proposed alloys are studied in detail. Firstly, the mechanisms of corrosion initiation, propagation and failure will be revealed by investigating the corrosion morphologies and monitoring the distribution of local corrosion current. And then, the effect of Al/Zn element, solution treatment and second phases on the corrosion behaviors is further illuminated systemically. Secondly, the growth mechanism and stability of corrosion surface film will be analyzed by investigating the morphologies, structure, composition, repassivation after scratching and coupled electrochemistry-spectral information. Thirdly, stress corrosion behaviour will be elucidated by the coupled mechanical-electrochemical-microstructural technology, containment with revealing the coordinated relation of mechanical property, electrochemical property and microstructure evolution. Thus, the current project will not only elucidate the corrosion behaviors and surface film of high-strength BCC Mg-11Li-xAl/Zn alloys, but also provide the novel method and technological support for the optimized design and application of high-strength and high-corrosion-resistant BCC Mg-Li alloys in the near future.

镁锂合金是最轻的结构用金属材料，然而低的绝对强度和差的耐蚀性一直是制约其发展与应用的瓶颈问题。本项目针对新型可固溶热处理强化的BCC结构Mg-11Li-xAl/Zn合金，系统研究其静态腐蚀与应力腐蚀行为、失效机制及表面膜。首先，通过腐蚀形貌的微观表征、原位观察和局部腐蚀电流分布的动态检测，揭示合金静态腐蚀萌生与扩展机制，阐明Al/Zn合金元素、固溶热处理和第二相等对腐蚀损伤的影响规律；然后，通过表面膜的形貌、结构、成分、损伤再钝化行为、电化学-光谱学信息等研究，分析表面膜动态生长机理及其物理化学特性；最后，利用力学-电化学-微观观察耦合技术研究材料的应力腐蚀行为，探明材料力学-腐蚀-微观组织的内在协同作用关系。本项目的实施不仅深入表征了高强BCC结构Mg-Li-Al/Zn合金的腐蚀行为及其表面膜特性，也为高强高耐蚀Mg-Li合金的设计与应用提供了新的思路和技术支撑。

镁锂合金作为最轻的结构用金属材料，具有高比强度、高比刚度、电磁屏蔽性能好等优点，具有重大的理论研究价值和工业应用前景。然而，镁锂合金绝对强度较低和耐腐蚀性能差等缺点严重限制了其广泛应用。本项目系统研究BCC结构Mg-11Li-xAl/Zn合金的微观组织、静态腐蚀与应力腐蚀行为、失效机制及表面膜。结果表明，Zn的添加可以有效调控Mg-11Li基合金的组织性能，发现软化相θ (MgLiZn)和硬化相θ’ (MgLi2Zn)可以在合金中协同析出，并同步提升其强度和塑性。固溶处理后，θ相消失，而更多细小的θ’析出，从而使铸态Mg-11Li-6Zn合金的抗拉强度提高了72 MPa，达到235 MPa。在腐蚀行为研究中，发现少量Zn可提高Mg-11Li合金在NaCl溶液中的耐蚀性和耐应力腐蚀性能，而过多Zn的添加，引起第二相与基体之间的微电偶腐蚀，降低了合金耐蚀性。固溶处理可以显著提升合金的耐蚀性，这主要归因于大块第二相的消失。对腐蚀膜层研究，发现由较厚的外层和较薄的内层组成的双层膜结构在少量Zn合金化的Mg-11Li-1Zn表面形成，并且少量Zn可以提升膜层的保护功能，从而提高合金的耐蚀性。另外，BCC结构镁锂合金的表面膜可在低过阳极电位下原位动态形成，并抑制负差数效应（NDE），而高阳极过电位下表面膜将会分解。关于Al元素对Mg-11Li系列合金力学与腐蚀性能的影响，其与Zn元素具有相似的效果和作用机制。本项目的实施不仅深入表征了高强BCC结构Mg-Li-Al/Zn合金的腐蚀行为及其表面膜特性，也为高强高耐蚀Mg-Li合金的设计与应用提供了新的思路和技术支撑。