多元镁合金电化学腐蚀机理的热力学研究及其应用

The wide application of magnesium alloys has been limited due to their poor corrosion resistance. Electrochemical corrosion is one of the most common type in the area of corrosion.The alloy composition has very large effect on the corrosion resistance of the magnesium alloys. In the Mg-based alloys for engineering, multicomponent and multiphases are included. However, it is scarce in literature on the sysmatical thermodynamic investigation for the electrochemical corrosion of the magnesium alloys. The present work aims to thermodynamically investigate the electrochemical corrosion of the important Mg-Al-Zn-Mn magnesium alloys by the coupling of CALPHAD method, first principles calculations and electrochemical experiments. Based on the developed scientific method by coupling thermodynamic calculations, first-principles calculations and key experiments,we will investigate the reaction mechanism of the electrochemical corrosion and the thermodynamic properties of the corrosion products. Thermodynamic models on the products of the electrochemical corrosion will be discussed and constructed based on the results from calculations and experiments. Gibbs energy of the corrosion products will be described as the function of alloy composition and temperature. A thermodynamic database including all the related phases (alloys phases,ionic aqueous solution,the solid phases that would formed as a result of the electrochemical reactions and the gaseous mixture phase) in the corrosion reactions will be then developed.Thermodynamic calculations will be performed based on the constructed thermodynamic database and the pourbaix diagrams for various alloys compositions and temperatures will be given. Based on the amount thermodynamic calculations, the effect of the alloy composition on the corrosion resistance will be discussed. And finally the optimal alloy composition with the excellent corrosion resistance of the Mg-Al-Zn-Mn alloys is expected to be obtained.The completion of this project will expand the CALPHAD technique to the research field of corrosion resistance of the magnesium alloys and provide design criterion for the improvement of the corrosion resistance of magnesium alloys.

镁合金的耐腐蚀性能欠佳极大限制了它的广泛应用，电化学腐蚀是镁合金工程应用中最常见的一种腐蚀类型，合金成分对其影响很大。工程用镁合金多为多组元体系，包含的元素和相较多，目前缺乏关于这一过程的系统热力学报道。本项目以镁合金中重要的Mg-Al-Zn-Mn体系为对象，通过热力学计算、第一原理计算和关键实验的耦合系统研究镁合金电化学腐蚀相关的热力学基础问题，拟开展如下具体研究：（1）发展耦合热力学计算、第一原理计算及关键实验的科学方法研究电化学腐蚀的反应机理并获得腐蚀产物的热力学性质；（2）建立合理的描述多元镁合金电化学腐蚀产物的吉布斯自由能随温度和成分变化的热力学模型，开发包含镁合金-溶液-腐蚀产物的热力学数据库；（3）计算不同合金成分和温度下的Pourbaix图，分析合金成分对多元镁合金电化学腐蚀的影响机理，为寻找能显著改善Mg-Al-Zn-Mn合金耐腐蚀性能的合金成分提供科学方法。

镁合金的耐腐蚀性能欠佳极大限制了它的广泛应用，电化学腐蚀是镁合金工程应用中最见的一种腐蚀类型，合金成分对其影响很大。针对工程用镁合金多为多组元体系，包含的元素和相较多，而文献中缺乏相关过程系统热力学报道的现状，本项目以镁合金中重要的Mg-Al-Zn-Mn体系为对象，通过热力学计算、第一原理计算和关键实验的耦合系统研究镁合金电化学腐蚀相关的热力学基础问题。通过项目的实施，项目组成员完善了Mg-Al-Zn-Mn体系的热力学描述并考虑原料中Fe杂质对镁合金耐腐蚀性能的影响，根据文献和本项目的工作构建了Mg-Al-Zn-Mn-Fe热力学数据库。基于构筑的热力学数据库，项目组开展热力学计算，据此设计并制备了不同成分的合金，通过腐蚀形貌观察、析氢（或失重）测试以及电化学腐蚀实验等研究了元素添加对镁合金腐蚀性能的影响及微观机理。此外，项目组尝试采用CALPHAD方法建立了X-O(X=Al、Mg、Zn)氧化物的热力学数据库并采用第一原理计算探索Al、Zn、Mn对Mg合金腐蚀影响的微观机理。项目的开展旨在基于热力学理论和电化学实验分析合金成分对多元镁合金电化学腐蚀的影响的微观机理，为寻找能显著改善Mg-Al-Zn-Mn合金耐腐蚀性能的合金成分提供科学方法。