| Nowadays, transportation is popular and being proceeded in the global range. Considering time, efficiency, and economic problems, the plane would play an important role in the transportation industry. TC18titanium alloy, which is a new type of high strength titanium alloy containing a+β two phases, has many virtues such as:high strength, plasticity and welding etc, and can be widely used in the manufacture of aircraft engine or its structural components.300M steel and30CrMnSiNi2A steel, which are medium carbon low alloy high strength steel, are wildly used in Chinese aviation industry, and are mainly used for the aircraft landing gear and bearing structure because of its good plasticity, toughness and anti-fatigue and fracture properties.7050aluminum alloy and7475aluminum alloy belong to Al-Zn-Mg-Cu alloy series and now are served as key parts of the plane.17-7PH stainless steel (0Cr17Ni7Al) belongs to precipitation hardening high strength stainless steel with good anti-corrosion performance, and improves the service life of aeroplane and reduces the period of maintenance. TC18titanium alloy, with positive potential, can result in accelerating corrosion of other materials when it contacts with other materials (such as steel and aluminium alloy) in the corrosive environment.Thus, corrosion will be a serious threat to the security of airplane. Therefore, it is of particularly importance to research contact corrosion and protection of TC18titanium alloy contacted with other metal in marine atmospheric environment, which will provide theoretical basis for its application.The main purpose of this paper is to study the galvanic corrosion of TC18titanium alloy and5kinds of material with different surface treatment which have been exposed respectively in marine atmospheric environment of Hainan and Qingdao for one year. The exposure samples and non-exposure samples of300M steel,30CrMnSiNi2A steel,7050aluminum alloy,7475aluminum alloy and17-7PH stainless steel have been processed by tensile and fatigue performance test. Then, the test datum are analyzed by the statistical analysis to find whether there are significant difference, and the microstructure and corrosion degree, surface corrosion morphology and fracture morphology are used to analyze the measuring results. In addition, the protective functions and effects of contact corrosion about the lay of paint and glue are analyzed in marine atmospheric environment, as well as the material fracture mechanism. The results of the study drawn as follows:After being exposed for one year in marine atmospheric environment, the tensile strength of300M steel,30CrMnSiNi2A steel,7475aluminum alloy and17-7PH stainless steel are unaffected.However, tensile strength of7050aluminum alloy is affected significantly by the T test analysis. The tensile-fractured morphology of the300M steel,30CrMnSiNi2A steel andl7-7PH stainless steel belong to the micro void coalescence fracture mechanism. And the tensile fracture of7050and7475aluminum alloy belong to a mixed fracture mechanism composed of micro-void coalescence and ductility fracture.Whether assembled or not, corrosion performance of300M steel in Hainan have slightly serious than that in Qingdao, thus resulting in poor fatigue lives of the samples in Hainan.30CrMnSiNi2A steel samples exposed for one year almost have not been corroded and their fatigue lives does not decrease, which indicate that phosphate layer and paint layer can effectively prevent atmosphere corrosion and contact corrosion of30CrMnSiNi2A steel. The non-paint samples of7050aluminum alloy and7475aluminum alloy have been exposed in marine atmospheric, whose surface pitting is uniformly distributed. The place of joint with TC18titanium alloy has more corrosion and generates gray powder corrosion products, but the samples with painting process have no obvious corrosion. Whether painted or not, or assembled or not, the fatigue lives of two kinds of aluminum alloy are affected significantly by marine atmospheric corrosion, and the fatigue lives of samples with painting process are slightly shortened, indicating that painting process prevents atmospheric corrosion and galvanic corrosion in a certain extent.17-7PH stainless steel has been exposed in Qingdao and Hainan marine atmospheric environment respectively, its fatigue life is not affected unless it was painted or cemented assembled. The results show that17-7PH stainless steel has very good resistance performance of marine atmosphere corrosion.The fatigue crack of the metal connected with TC18titanium alloy originates from the surface corrosion area of the sample. Cl, S and O elements occupy the main position on material corrosion. The fatigue crack propagation zone and final fracture zone of all the materials are not affected by marine atmospheric corrosion. The fatigue crack propagation of the300M steel shows herringbone pattern, and there are many obvious intermittent fatigue lines, in wihch the second propagation cracks are mostly present. In addition, there are small facets in the propagation zone which show quasi cleavage fracture characteristics. The fatigue crack propagation zone of30CrMnSiNi2A steel exists the second crack, and there are many toughness cavities in the final fracture zone of30CrMnSiNi2A steel, which are caused by the micro-void coalescence fracture. The fatigue striations of the fatigue crack propagation zone of7050and7475aluminum alloy are relatively obvious and regular. The toughness cavity and quasi cleavage step can be observed from the final fracture zone of7050and7475aluminum alloy, which belong to the quasi-cleavage and empty gathered mixed fracture mechanism. The fatigue crack propagation area of17-7PH stainless steel exists small facet, which shows quasi cleavage fracture characteristic. There are a large number of small irregular fatigue striations near the crack propagation area, but the fatigue striations far away become long, clear and regular. The feature of interruptions area is the great and deep tough nest, which caused by the micro hole formed together induced by the second phase. |
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