镁合金表面金属/陶瓷复合防护层的设计制备及其防腐蚀性能研究

Based on the idea of synergistic protection of the metallic layer and non-metallic layer on magnesium alloy, a metallic/ceramic duplex layer is proposed to improve the corrosion protection properties of single layers in this project. The metallic/ceramic duplex layer is produced by combined laser surface modification and plasma electrolytic oxidation (PEO) processes owing to their specific advantages in surface treatments for magnesium alloys. Firstly, a metallic layer with the compositions, phases and microstructures different from magnesium alloy substrate can be produced using the laser surface modification process. Secondly, the laser modified metallic layer is treated by PEO process to form a top oxide ceramic layer. As a result, a metallic/ceramic duplex layer that consisted of laser modified inner layer and PEO treated top layer with desired microstructures and compositions is successfully produced on magnesium alloy. The effects of laser surface modification and PEO process conditions on the structures, compositions and corrosion protection properties of the metallic/ceramic duplex layer on magnesium alloy are systematically studied. The corrosion protection behavior of the duplex layer in the typical corrosive environments is also investigated. The mechanisms of synergistic protection and degradation/failure of the duplex layer in corrosive environments is then discussed based on the analysis of the structure-properties relationship. Finally, the model of degradation/failure processes and the principles/methods of prolonging the corrosion protection properties of the duplex layer are presented to achieve the effective control for the preparation processes and properties of the duplex protective systems.

针对镁合金单一表面防护层腐蚀防护性能不足的问题，本项目基于金属防护层与非金属防护层相结合以实现协同防护的设计思路，充分利用激光改性与微弧氧化在镁合金表面处理中的独特优势，首先通过激光表面处理对镁合金进行表面化学成分、相组成或微观结构的重构，形成一层不同于镁合金基底的金属层，然后采用微弧氧化方法对激光处理金属层实施表面氧化（陶瓷化）处理，在镁合金表面制备得到以激光改性金属层为中间层而微弧氧化陶瓷层为表面层且结构、成分可控的金属/陶瓷二元复合结构防护体系。研究激光处理与微弧氧化工艺条件对金属/陶瓷复合防护体系结构、成分及腐蚀防护性能的影响，阐明典型腐蚀环境中金属/陶瓷复合防护体系的腐蚀防护行为，深入分析复合防护层结构/成分与性能之间的关系规律并揭示其协同防护机制及损伤失效机理，提出其损伤失效模型和延寿原理与方法，实现具有优异腐蚀防护性能的新型复合防护体系制备与性能的有效控制。

本项目通过将激光改性与微弧氧化技术相结合，在AZ91D镁合金表面制备新型“金属+非金属”复合结构来提高镁合金单一表面防护层的耐腐蚀性能。通过对AZ91D镁合金进行激光改性（激光熔凝和激光合金化）处理制备了厚度范围为500~1500 μm的改性层，激光改性使镁合金表面发生了组成的变化和微结构的重构，优化制备参数可一定程度地提高基体的耐腐蚀性能。对经激光熔凝改性处理的AZ91D镁合金进行微弧氧化（LSM-PEO），形成了以激光改性金属层为中间层而微弧氧化陶瓷层为表面层的金属/陶瓷复合结构防护层。与AZ91D镁合金直接微弧氧化处理（PEO）制备的氧化膜相比，经激光熔凝前处理的氧化膜结构致密性增加。通过考察直接PEO处理和LSM-PEO处理镁合金的耐蚀性能，阐明了微弧氧化陶瓷层和金属/陶瓷复合结构防护层的腐蚀防护性能失效过程，探究了两者的腐蚀防护机理并建立了防护失效机制模型。结果表明，金属/陶瓷复合结构防护层显著提高了微弧氧化陶瓷层的长效腐蚀防护性能，延缓了镁合金开始发生腐蚀的时间。本项目的研究结果对于开发新型复合结构防护层，解决镁合金表面微弧氧化陶瓷层长效腐蚀防护性能不足的关键问题等方面具有理论指导意义与应用参考价值。