Marine corrosion and protection is an important issue in the development of the ocean, because the erosion of the ocean atmosphere and seawater is an important cause of damage to coastal facilities, offshore engineering structures, and ships. Therefore, studying the corrosion resistance and long-term protection technology of buildings in the marine environment is of great strategic significance for human development of the ocean and the use of the ocean.
A large number of research and application results at home and abroad show that thermal spraying of aluminum, zinc and alloy coatings is the most effective and economical protection method. Because aluminum, zinc and aluminum-zinc alloy coatings have excellent corrosion resistance, aluminum and zinc are anode materials for steel. Even if the coating is slightly defective, the steel substrate is protected from corrosion by sacrificial anodes. Aluminum zinc is widely used as an anticorrosive coating for steel components. Thermal coating of aluminum, zinc and alloy coatings can therefore be used to provide long-term protection against steel components and structures. This paper briefly introduces the specific application of thermal spray aluminum zinc and its alloys in the marine environment for reference by enterprises, research institutions and related personnel.

I. Research and application of thermal spray aluminum and zinc in the UK The UK is one of the earliest countries to apply thermal spray anti-corrosion technology. In 1939, the thermal spray zinc coating method was used for the first time to protect the steel chain and part of the steel structure of the new Welsh Menai Strait Bridge. The sprayed zinc coating has a thickness of 0.125 mm and the paint is sealed. After 15 years, the zinc coating was basically intact, and the steel substrate was well protected without repair. In 1989, British author J. C. Bailey and other papers presented at the 12th International Thermal Spray Conference mentioned that after 50 years of use, the steel matrix of the Menai Strait Bridge is still well protected. After 1956, the United Kingdom began to implement thermal spray zinc coating anti-corrosion treatment on the newly built bridge. The Forth Road Bridge in Qucesferry, Scotland, is a windy marine environment with a bridge length of 3.6 km and was built in 1964. The bridge adopts anti-corrosion technology, which is phosphating primer and thermal spray zinc chromate coating, and then coated with micaceous iron oxide topcoat. After 13 years of use, the bridge has no maintenance, the protective layer has good color, and only a small amount of paint is peeled off. service. The anti-corrosion method using the thermal spray zinc coating can effectively prevent the steel components from coming into contact with the asphalt pavement, causing rust and corrosion, and reducing the risk of breakage and damage of the bridge.
In 1926, the United States built the Mormon Flat Reservoir on the Salt River in Arizona. In 1937, two 15 m wide x 15 m high spillway gates were installed. With the change of reservoir water level, the gate is sometimes soaked in water, sometimes exposed to the sun. From the perspective of economic interests and safety, effective anti-corrosion measures must be taken to ensure the longest service life of the reservoir. After repeated argumentation, it was finally decided to adopt a thermal spray zinc coating scheme. To ensure a 40-year coating life, the staff initially expected the thickness of the zinc coating to be at least 0.175 mm. Considering that the collision of floating objects on the water surface will damage the raised rivets on the gate and the zinc coating on the weld area, in order to fully exert the cathodic protection of the zinc coating, the coating can be partially damaged in some areas. In this case, there is still a protective effect on these damaged areas, and it is decided not to paint any coating on the surface of the zinc coating. The thickness of the coating is between 0.175 mm and 0.25 mm. In March 1992, the reservoir managers decided to carefully inspect them. At this time, the water level of the reservoir is lower than the previous minimum water level line of 1 meter, which can well check the coating condition in the vicinity of the water level line of the gate. The inspector saw that there was no rust on the surface of the gate, the surface of the zinc coating was in good condition, there was no white rust (corrosion product of zinc), and there was no obvious uneven corrosion of the zinc coating; although the rivet head, weld and other raised parts After the surface floats are scratched, the surface zinc coating is broken and the steel substrate is exposed, but the steel substrate does not show any visible signs of corrosion. The inspectors used a coating thickness gauge to detect multiple coating thicknesses. The measurement results showed that except for a very small number of coating thicknesses of 0.1 mm, the thickness values ​​of the remaining points were between 0.175 mm and 0.25 mm, and 22 There was almost no major change in the thickness of the original spray before the year. It can be seen that the zinc coating plays a very good role in protecting the corrosion of the reservoir gate.
In June 1984, the United States used thermal spray aluminum coating technology to protect the tethers, elevators, and conical towers of tension strut platforms in Hutton production facilities in the North Sea, because for these high-strength steel parts, the flame The sprayed aluminum coating not only provides an aluminum shielding layer, but also acts as a sacrificial anode to protect the leaked coating area if the coating is damaged; a flame retardant coating can be applied to the flame sprayed layer to seal the flame spray aluminum coating. The pores of the layer improve the performance of the coating and extend its service life. After 8 years of use on the Hutton platform, no corrosion and brown leakage effects were observed in the splash zone. The thickness measurement showed that the thickness of the coating did not decrease after the platform was installed. It was found by the tensile and scribing tests that the bonding strength of the coating was very high (between 10.35 and 13.8 MPa), and the original aluminum blasting substrate was still removed. The state indicates that the Hutton platform after thermal spray aluminum coating has good corrosion resistance.

Second, the domestic research and application of thermal spray aluminum zinc <br> China began to promote the application of thermal spray anti-corrosion technology in the 1980s, the system research and test of the technology started late. In 1983, the Wuhan Institute of Materials Protection of the Ministry of Machinery Industry was responsible for the electrochemical testing of thermal sprayed zinc, aluminum and its alloy coatings. The seawater corrosion test in different sea areas in eight typical regions of the country, the Yangtze River Three Gorges Freshwater corrosion test in waters. Through the analysis of the test results, it provides a reliable basis for the large-scale popularization and application of thermal spray anti-corrosion technology in China.
In 1984, the Nanjing Hydraulic Research Institute designed the metal protection of 16 32 m span coal loaders' railway beams by the 10×104 t open dock in Shijiu Port, Shandong Province. Because the area is usually rough, the structure is low from the sea level, and the corrosive environment is harsh, the scientists designed the coating as: flame spray aluminum plus phosphating primer 27. 5 μm, epoxy micaceous iron oxide 40 ~ 50 μm Acrylic polyurethane topcoat 30 μm anti-corrosion protection, the total thickness of the sealing layer is 80-90 μm. In 1987, it was identified by the Ministry of Communications that the anti-corrosion effect was significant, and it is expected that overhaul is not required for 20 years. In 1994, the entire steel beam was inspected for no rust.
In 1986, the high-aluminum-zinc-based alloy wire developed by CSSC 725 was sprayed to the outside of the side of several barges by the flame thermal spraying technique in the marine atmosphere and the splash zone (the thickness of the metal coating was about 150 μm). The organic coating is sealed. In 2004, a barge that was still in service was inspected and found to be completely preserved in the marine atmosphere. The zinc-aluminum coating near the waterline in the spray splash zone was basically consumed, and a large amount of white zinc-aluminum metal corrosion products appeared. However, the steel matrix did not show obvious rust.

III. Conclusion <br> Thermal spraying of zinc-aluminum and its alloy coatings has become a mature protection technology for offshore and marine steel facilities. The steel is in the splash zone at normal temperature and high temperature through a properly closed thermal spray aluminum coating. The structure exhibits excellent corrosion resistance. According to the current state of the art, the 200 μm thick thermal spray aluminum coating is expected to have a protective life of more than 30 years in the splash zone. China's thermal spraying anti-corrosion technology started late, this effective protection method has not attracted widespread attention. In the severely corrosive marine environment, the long-term protection application of thermal spraying of steel facilities is still relatively rare in China, and needs to be further promoted. application. Therefore, the development and research of this technology has a great impetus to the economic development of our country.

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