航空低压环境对镁合金气化强化氧化和燃烧特性的影响研究

The potential flammability of magnesium alloy seriously hinders its further application in the aviation field. It is of great significance to study the influence of aviation low-pressure environment on the combustion characteristics of magnesium alloy for aircraft weight reduction design. The high saturated vapor pressure of magnesium has a certain strengthening effect on the whole oxidation combustion process of magnesium alloy and has the greatest influence on the incubation period before the ignition of magnesium alloy. Environmental pressure has a significant influence on the gasification-enhanced oxidation process and combustion characteristics of magnesium alloys, but the specific mechanism has not been systematically revealed. This project takes pure magnesium and different brands of magnesium alloys as the research object, and focuses on solving two scientific problems: 1.Effect of aviation low pressure environment on surface oxidation film rupture and subsequent combustion process, 2.How to quantify the combustion performance of magnesium alloys caused by alloying elements. Through the study of this project, it is expected to obtain the key parameters such as the critical rupture pressure of the initial oxide film, reveal the influence mechanism of pressure on the oxidation process of gasification-enhanced oxidation, and establish the combustion characteristics prediction model with temperature and environmental pressure included. The influence mechanism of different alloying elements on the mechanical properties and micro structures of the initial oxide films can be clarified. The influence of aviation low-pressure environment on the fire hazard of magnesium alloy was quantitatively can be analyzed. The research of this project is expected to promote the further application of magnesium alloys in the field of aviation.

镁合金材料潜在的可燃性严重阻碍了其在航空领域的进一步应用，研究航空低压环境对镁合金燃烧特性的影响对航空器减重设计具有重要意义。镁较高的饱和蒸气压对镁合金的整个氧化燃烧过程存在一定的强化作用，对镁合金被点燃前的潜伏期阶段影响最大。环境压力对镁合金气化强化氧化过程和燃烧特性具有显著影响，但具体机理尚未得到系统揭示。本项目以纯镁和不同牌号的镁合金材料为研究对象，重点解决两个科学问题：①航空低压环境对表面氧化膜破裂和后续燃烧过程的影响机理；②如何量化合金元素导致的镁合金燃烧性能的变化。通过本项目的研究，可望获得初始氧化膜临界破裂压力等关键参数，揭示压力对气化强化氧化过程的影响机理，建立耦合温度、环境压力的燃烧特性预测模型；明确不同合金元素对初始氧化膜力学特性和微观形貌的影响机理，继而量化分析航空低压环境给镁合金火灾危险性带来的影响。通过本项目的研究，可望推动镁合金材料在航空领域的进一步应用。

本项目针对镁合金材料在航空领域迫切的应用需求，分析了环境压力、合金元素、外界辐射等参数对气化强化氧化潜伏期时间的影响，获得了初始氧化膜破裂关键参数及破裂行为特征。分析了不同合金元素添加对氧化膜生长的影响机理，建立了镁/镁合金高温腐蚀燃烧全过程传热传质模型，综合分析了镁合金材料在低压情况下的燃烧特性变化。研究结果表明，镁/镁合金在高温下发生剧烈氧化/氮化反应时由于氧气和氮气浓度梯度的存在，二者存在一定的竞争机制，趋向于形成外层氧化镁内层氮化镁的多层产物结构。压力对高温腐蚀速率的影响是非线性的，压力带来的氧浓度降低是影响腐蚀速率的一个重要因素。在表面氧化膜破裂之前，高温腐蚀时间和腐蚀温度会直接影响到表层Mg的腐蚀速率，从而直接影响表面吸收率，而环境压力则是通过氧浓度来影响氧化反应速率，进而影响表面吸收率，这三个因素耦合决定了镁合金材料的表面换热系数，进而决定了升温速率。氧化膜破裂之后则只有环境压力带来的氧浓度变化会对反应速率产生影响，从而表现出不同的燃烧特性。通过量子化学计算分析了不同合金元素对镁合金表面氧化膜组分和结构的影响机理，稀土元素的添加可以有效吸附氧原子并形成稀土氧化物，致密的稀土氧化物有助于提高镁合金表面氧化膜的强度，从而提高合金的耐高温性能。此外，本项目对镁合金材料在飞机客舱内可能发生的熔融滴落和流淌火蔓延行为开展了初步研究，结果表明镁合金材料的熔融滴落行为与有机固体可燃物类似，可燃固体表面的液体火蔓延速率会有所降低。