Influence of assembly on corrosion behaviors of bolt/nut connections in a salt-spray environment
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摘要: 海軍航空裝備的快速發展導致飛機必將面臨更為嚴峻的海洋大氣腐蝕問題，而軍用飛機緊固件的腐蝕，尤其電偶腐蝕將嚴重影響飛機結構的安全性水平.因此，本文采用鹽霧腐蝕模擬、掃描電鏡觀察與分析、電化學測試分析（自腐蝕電位測試、動電位極化測試、電偶腐蝕電流測試）等試驗研究方法，將航空裝備常用的30CrMnSiA鍍鎘鈍化螺栓與三種不同螺母（30CrMnSiA鍍鎘鈍化螺母、30CrMnSiA鍍鋅鈍化螺母和0Cr16Ni6鈍化螺母）偶接裝配，研究由于裝配導致的電偶腐蝕效應對典型螺栓/螺母緊固件腐蝕行為的影響.結果表明，在三種不同組合裝配中，30CrMnSiA鍍鎘鈍化螺栓與0Cr16Ni6鈍化螺母之間電位差最大，電偶腐蝕電流密度最高，對應螺栓電偶腐蝕敏感性評級達到E級，電偶腐蝕作用促進了鍍鎘鈍化螺栓基體表面點蝕的擴展，腐蝕進程被加速，加速系數AF達到3.4；30CrMnSiA鍍鎘鈍化螺栓與30CrMnSiA鍍鋅鈍化螺母之間電偶效應則較弱，且螺母為電偶腐蝕陽極，腐蝕進程被加速，加速系數AF為1.2，電偶腐蝕敏感性評級為D級；相比上述兩種組合，30CrMnSiA鍍鎘鈍化螺栓與30CrMnSiA鍍鎘鈍化螺母之間電偶效應最不明顯，對應電偶腐蝕敏感性評級為A級.Abstract: Due to the rapid development of naval aviation equipment, naval aircraft will encounter complicated atmospheric corrosion problems resulting from exposure to the oceanic atmosphere. The corrosion of the fasteners in the aircraft, especially due to the galvanic corrosion between fasteners, seriously compromises the safety of a particular component in an aircraft. When an aircraft is used for a long duration in an oceanic atmosphere containing high humidity and salinity, a layer of liquid film having a thickness of less than 1 μm will form on the surface of the structure, which causes electrical conduction between different structures, thereby increasing the risk of galvanic corrosion. Currently, many studies mainly focus on investigating the stress corrosion cracking (SCC) of bolt or galvanic corrosion between the bolt and aluminum alloy plates. However, only a few studies have investigated the galvanic corrosion of bolt/nut in assembly. Therefore, three types of nuts (Cd-plated 30CrMnSiA, Zn-plated 30CrMnSiA, and passivated 0Cr16Ni6) were utilized in this study, which were assembled to a Cd-plated 30CrMnSiA bolt. The salt-spray corrosion simulation, observations from scanning electron microscope (SEM), and electrochemical measurements (open circuit potential, potentiodynamic polarization, and galvanic corrosion current tests) were used to investigate the effect of the galvanic corrosion between the bolt/nut couples on the corrosion behaviors of bolts and nuts. The results depict that the highest potential difference and galvanic current are observed between the Cd-plated 30CrMnSiA bolts and passivated 0Cr16Ni6 nuts, which indicates the most significant galvanic effects. Further, the galvanic corrosion sensitivity rating reaches an E level, which significantly promotes the propagation of the pitting corrosion of the bolt. Additionally, the acceleration factor (AF) becomes 3.4. For the couple including the Cd-plated 30CrMnSiA bolt and Zn-plated 30CrMnSiA nut, the nut acts as an anode. Further, the corrosion rate of the nut increases, and the AF approximately becomes 1.2. Compared to the aforementioned two couples, the Cd-plated 30CrMnSiA bolt and 30CrMnSiA nut exhibit the weakest galvanic effect, and the galvanic corrosion sensitivity rating is observed to be at an A level.
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Key words:
- galvanic corrosion /
- bolt/nut /
- assembling /
- Cd plating /
- Zn plating /
- passivation
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參考文獻
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