【作者】 何建平；

【导师】 樊蔚勋；

【作者基本信息】 南京航空航天大学 ， 飞行器设计， 2002， 博士

【摘要】 超硬铝合金是重要的航空结构材料，广泛用于军用飞机和民用飞机的大梁、桁条、隔框等承力部位。由于环境腐蚀介质的侵蚀不可能完全避免，因此，有关超硬铝合金构件的腐蚀损伤，仍然是航空领域中十分重要的研究内容。 超硬铝合金在环境中的损伤，绝大多数情况下属于剥离腐蚀。超硬铝合金表面状态、环境条件的变化，均可能改变剥蚀的发展过程，为此，本文提出在恒温条件下，用电位法、电阻法定量研究铝合金的剥蚀性能。实验结果显示了LC4CS铝合金的自腐蚀电位与时间的关系，和腐蚀速率与时间的关系有着十分相似的规律，两者均在120分钟前后有不同的变化。从自腐蚀电位的变化规律可以推断，在腐蚀的初期阶段，铝合金表面自然生成的钝化膜逐渐溶解，使铝合金腐蚀速率快速增加。当腐蚀浸泡的时间大于120分钟后，腐蚀产物在铝合金表面产生了明显的位阻作用，从而使腐蚀速率逐渐下降，直至48小时后，腐蚀速率趋于一相对稳定的数值。 铝合金受外力作用，有可能裸露出新鲜金属，新鲜金属与其余已钝化的部分之间，存在耦合作用。实验结果显示，新鲜金属的自腐蚀电位随时间的增加而逐渐增大，如果时间足够长，自腐蚀电位将趋于稳定的数值。耦合状态下，新鲜金属的耦合电位正向移动的速率极快，在40秒钟后已接近于铝合金稳定的自腐蚀电位。根据耦合作用理论，获得了耦合电位、裸露的新鲜金属腐蚀速率的数学表达式，数学模拟所得的耦合电位与时间的关系，和实验结果有较好的一致性。 将上述耦合理论应用于铝合金的裂纹尖端，并据此研究裂尖的电化学行为，发现铝合金新鲜表面的溶解速率随应变速率的增加而增大。应变速率愈大，耦合电流随时间增大的速率也愈快，但几乎均在应变量为0.04左右时，耦合电流呈急剧增大的趋势。 腐蚀减少了铝合金构件总的承载能力，也对其强度产生影响。环境介质的组成、形态是影响腐蚀疲劳裂纹扩展的重要因素。3.5％NaCl溶液和3.5％NaCl薄液层的化学组成几乎完全相同，只是薄液层中氧的传质速率较快。实验结果显示了在薄液层中，LC4CS铝合金的湿腐蚀疲劳裂纹扩展速率，大于在3.5％NaCl溶液中的速率。实验还发现其疲劳断口的形貌，也与3.5％NaCl溶液中的有明显区别。阳极氧化是提高铝合金耐蚀能力的常用方法，如果从疲劳性能的角度考虑，经硫酸阳极氧化的铝合金腐蚀疲劳性能比铬酸阳极氧化的更好一些。 再将“耦合作用”的猜想，引入铝合金的腐蚀疲劳裂纹扩展过程中，用电化学的方法测定耦合电流与加载时间的关系，并从理论上导出LC4CS铝合金应力腐蚀裂纹扩展速率的数学表达式，数学模拟的结果与实验值具有较好的一致性。更多还原

【Abstract】 Super-duralium that is widely used for the longerons, frames, stringers of military and civil aeroplanes, is an important aeronautic material. Because fully avoiding of environmental erosion is difficult, the research on the corrosion damage of the super-duralium is still one of the affairs of the first magnitude.The damage of super-duralium caused in environment is mostly exfoliation corrosion. The variations of the surface state and environment conditions could change the procedure of exfoliation, therefore, the potentiometry and electric resistance methods in this paper are used to measure the exfoliation rate of Aluminum alloys in a constant temperature, the experimental results show that relations of natural corrosion potential vs time have a resemblance to those of corrosion rate vs time, both relations are all at the different change rates in the front and back of 120 minutes. From the varieties of the natural corrosion potential of Aluminum alloys, it is deduced that the gradual dissolution of natural passive state film of the alloys brings about high-speed enhancement in the corrosion rate of the alloys. Because of the place obstruction of corrosion products in the surface of the alloys, while corrosion time is at 120 minutes above, the corrosion rate descends to the stable value in 48 hours.In the action of external force, Aluminum alloys could bare out fresh metal, so there are galvanic couple between the fresh metal and rest parts passivated. Electrochemical tests show that the longer time is, the higher natural corrosion potential of the bare metal is. If corrosion time is long enough, the potential will go to a stable value. In the state of galvanic couple, the couple potential of the bare metal quickly shifts towards positive direction, and to approach the stable natural corrosion potential of Aluminum alloys after 40 seconds. On the basis of couple polarization theory, the mathematical expressions of couple potential and corrosion rate of fresh bare metal are inferred, the theory modeling relations of couple potential vs time is corresponding to experimental results.The couple theory above-mentioned is applied at the crack tip of Aluminum alloys, on ground of the theory, the experiment on the electrochemical action at the tip shows that the faster the strain rate is, the quicker the dissolution rate of the fresh surface of Aluminum alloys is. the faster the strain rate is, the quicker the increment rate of couple current vs time is, while strain is equal to 0.04 about, the couple currents show the trend of sharp enhancement.Corrosion affects not only the loading capacity of Aluminum alloys component, but also the strength. The composition and modality of the environment medium play animportant role in the crack growth of corrosion fatigue. The formation of 3.5% NaCl solution is almost similar to that of 3.5% NaCl thin electrolyte layer, just the mass transfer rate of the oxygen in the layer is more quicker than in the solution ?The test shows that the crack growth rate of wet-corrosion fatigue of LC4CS Aluminum alloy in the layer is quicker than in the solution, and also shows that morphology of fatigue fracture in the layer is evidently distinguished from in the solution. The corrosion resistance of Aluminum alloys is improved by anodic oxidation, if the fatigue behaviors are taken into account, the behaviors of Aluminum alloys by sulfuric acid anodizing is better than by chromic acid anodizing.Furthermore, the supposition of galvanic couple is drawn into the procedure of corrosion fatigue crack growth of Aluminum alloys, the relation of couple current vs loading time is determined with electrochemical methods. A formula in the theory is deduced which expresses the stress corrosion crack growth rate of LC4CS Aluminum alloy, the results of mathematical modeling preferably correspond with examination.更多还原