Composite anti-corrosion technology of threaded fasteners in the sea environment of the bookmark0 Bian Feilong, Huang Yanbin1, Shi Xiaojun, Song Gaowei (Department of Equipment Remanufacturing, Academy of Armored Force Engineering, Beijing 100072, China) Vacuum zinc-zinc/zinc-chromium coating composite coating Program. The preparation process of composite coating layer was introduced in detail. The resistance of chemical forged Ni-P alloy forging layer, vacuum zinc coating layer, zinc chromium coating and vacuum zinc-zinc/zinc-chromium composite coating layer was compared by neutral salt spray test. Corrosive. The results show that the corrosion resistance of vacuum zinc-zinc/zinc-chromium composite coating is significantly better than that of electroless Ni-P alloy coating, vacuum zinc coating and zinc-chromium coating.
1 Proverbs The marine environment is one of the most corrosive environments in nature. Most metal materials are not resistant to seawater and oceanic atmospheres. Many threaded fasteners exposed to the marine environment for a long time are very corroded. Corrosion causes the fasteners to be difficult to disassemble, the joint strength is reduced, and even the direction is metal material corrosion and protection.
Loss and other problems have caused great difficulties in the normal service and maintenance of fasteners. According to the investigation, there are 200 fastening bolts on a certain type of marine engineering vehicle. When disassembling, the number of bolt breaks is up to 50, reaching 25%. Some bolts are disassembled, although they are not broken, but due to the screwing part Rusting makes disassembly very difficult and cannot be dismantled with a normal wrench. Corrosion protection of threaded fasteners in the marine environment has become an urgent problem to be solved.
By analyzing the fastener material, structural characteristics, use conditions and other factors, combined with the characteristics of marine environmental corrosion, threaded fasteners mainly have many types of corrosion such as crevice corrosion, galvanic corrosion, stress corrosion and fretting corrosion. The corrosion influencing factors are very complex. Due to its inherent limitations, a single surface technology cannot effectively solve the corrosion problems of fasteners. At present, the commonly used anti-corrosion coatings for threaded fasteners in the project include hot dip galvanizing, electroless Ni-P alloy plating, vacuum zinc infiltration, zinc chromium coating and the like. Among them, the hot-dip galvanizing anti-corrosion performance is general, the coating is thick, which is easy to cause the bolt and nut to be assembled. The vacuum zinc-plated layer has certain corrosion resistance, high bonding strength with the substrate, good wear resistance, but salt spray corrosion resistance. <300h; zinc chromium coating excellent corrosion resistance, salt spray test time 1000h, coating thickness <10 spleen, does not affect the assembly of fasteners, but the hardness is low, wear resistance is slightly poor. The analysis found that the latter two coatings have some complementarity in performance. In this context, the research on the composite process technology of vacuum zinc infiltration/zinc-chromium coating was carried out, and the neutral salt spray test was used to test the wear resistance and corrosion resistance of the composite coating.
2. Comparing a and b, it was found that after 5 times of screwing assembly, the color of the composite coating of the screw-bonding part of the fourth group of samples changed from silvery white to black, but no red rust appeared, indicating that the bolt substrate was not subjected to Corrosion; the rusting phenomenon of the screwing part of the third group of samples is more obvious, while the thread of the unspinning part has no rust spots, indicating that the multiple screwing assembly causes great damage to the zinc-chromium coating. It can be seen that the composite coating layer has a significantly better overall corrosion resistance than the zinc chromium coating.
4 Conclusions Threaded fasteners have serious corrosion phenomena in the marine environment. The first is that the corrosion rate is fast, the second is the influencing factors, and the third is the difficulty of maintenance. With a single protective coating, it is difficult to achieve effective corrosion protection.
The vacuum galvanizing/zinc-chromium coating composite method is used to solve the corrosion problem of fasteners. The neutral salt spray test proves that the comprehensive anti-corrosion effect is better than the electroless Ni-P alloy plating, vacuum zinc coating and zinc. Chrome coating. %
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