# Research on Corrosion Damage Evolution of Aluminum Alloy for Aviation
## 1 Introduction  
The 7075 ultra-high-strength aluminum alloy material has a series of advantages such as high specific strength, high specific stiffness, light weight, and so on. It is widely used in national economic construction and the national defense industry, especially in the aviation industry field, in which it plays an irreplaceable role [1, 2], such as aircraft wing panel, wing beam, wing rib, and fuselage internal support components [3]. However, with the growth of service time, a series of corrosion problems of 7075 aluminum alloy often occur in the atmospheric environment, especially in coastal areas. According to statistics, most aircraft in coastal areas are in combat readiness on duty (not working) status after being delivered for use, and their stopping time on the ground generally accounts for more than 97% of the total service time [4, 5]. Aluminum alloy materials on the surface of an aircraft airframe will suffer from corrosion damage to varying degrees under adverse conditions such as coastal salt fog, rain water, and humid air, and for the aircraft internal structure, due to its strong concealment, corrosion damage is often more easily ignored and the corrosion threat is greater. A large number ofstudies have shown that aircraft with corrosion damage are more prone to fatigue damage under the action of flight load [6; 7; 8; 9], which seriously threatens the flight safety of the aircraft. Therefore, it is very important to analyze and evaluate the corrosion damage of aluminum alloy materials in coastal areas and understand the evolution law of corrosion damage, which is very important to ensure the long-term service safety of aircraft, significantly in coastal islands and reefs. For the study of corrosion damage law, because outdoor atmospheric corrosion often has a long period and consumes a lot of manpower and resources, laboratory-accelerated corrosion methods are often used. For the accelerated corrosion method in laboratory, two contents need to be clarified. One is the selection of corrosion mode (full immersion, alternate immersion, salt spray, etc.) and the other is to determine the composition and concentration of corrosion medium in the corrosion solution. Because the alternate immersion test can better simulate the process of \"alternation of dry and wet\" atmospheric corrosion [10] and in order to restore the actual atmospheric corrosion environment more truly, the laboratory-accelerated corrosion method determined in this paper was as follows: Using the alternate immersion corrosion method, the components of various corrosive media, obtained from real monitoring in the Warning area of Hainan Province (coastal cities in China), were taken as the components of the corrosion solution in this test and the concentration of the corrosion medium monitored was weighed in equal proportion as the concentration of corrosion medium in the accelerated corrosion solution. As one of the most common corrosion damage forms in the early stage of aluminum alloy structure corrosion, pitting corrosion accounts for the highest proportion in all corrosion types. It does not have obvious corrosion morphology, like denudation, and the corrosion pits on the material surface are easily covered by corrosion products, so it is easy for people to neglect [11]. After pitting corrosion of aluminum alloy, the corrosion pits on the surface of the structure are often the crack source of corrosion fatigue and stress corrosion fracture, which directly affect the residual strength and fatigue life of aluminum alloy structure. Therefore, establishing a reasonable and reliable corrosion pits' evaluation index was the premise of corrosion damage analysis and evaluation. At present, there is no formed evaluation system for corrosion damage (corrosion pits) at home or abroad [12]. The damage tolerance design manual of the U.S. Air Force proposes that \"defect influence\" should be selected as the most ideal evaluation index for structural corrosion damage.