[Aluminum Road Network] Aluminum alloy has advantages of small specific gravity, high specific strength, good resistance to seawater corrosion, non-magnetic properties, and good low-temperature performance, and it has been receiving increasing attention as a structural material in the shipbuilding industry. Using aluminum alloy as the hull material can effectively reduce the weight of the ship, improve the stability and speed, and enhance the technical and tactical performance of the ship. For high-speed planing boats, hydrofoil boats, hovercrafts, small surface vessels and some special purpose vessels, the use of aluminum alloys is particularly suitable. With the development of inert gas welding technology of aluminum alloys, the continuous reduction of production costs, the advantages of aluminum alloy materials and the application in the marine environment are expanding, not only in the field of light ships, but also in the field of high-speed boats.
Aluminum and aluminum alloys are chemically active, but because they can form a dense, passivated oxide film with oxygen, they are much more corrosion resistant than steel. When an aluminum alloy is used on a ship, it is exposed to seawater more or less wherever it is used, or it is exposed to seawater droplets and the marine atmosphere, and is therefore subject to certain corrosion. Corrosion of aluminum alloys is a very complex process that is not only affected by the environment but also related to the nature of the alloy. The common corrosion types of marine aluminum alloys in the marine environment are: pitting corrosion, crevice corrosion, intergranular corrosion, exfoliation corrosion, and stress corrosion cracking.
Status Quo of Aluminum Alloy Corrosion Protection Technology for Ships
The marine environment is a harsh environment, and the requirements for corrosion protection of aluminum alloys in this working environment are higher. For ships, the corrosive environment is different in different parts. The bottom of the ship is mainly affected by the penetration of natural seawater and the adhesion of aquatic organisms. The parts above the waterline are mainly affected by salt spray corrosion and atmospheric aging.
Sacrificial anode cathodic protection
For small high-speed vessels, the applied current cathodic protection measures are generally not used. At present, it is common practice in foreign countries to install sacrificial anodes on the hull's exterior board (with anti-corrosion coating). Aluminum alloy itself is a very good sacrificial anode material compared to steel, copper and other materials; for aluminum hulls, it must be used for cathodic protection of aluminum alloy sacrificial anodes with sufficiently negative electrode potential, and at the same time, it is necessary to consider that the anode has good The dissolution characteristics and potential cannot be too high and cause alkaline corrosion of aluminum. At present, the main component of the aluminum alloy sacrificial anode material is Al—Zn—In—Mg—Ti; the sacrificial anode is fixed with bolts, the core of the iron core in the anode must use aluminum core, and the bolt must use aluminum bolts.
Aluminum alloy marine antifouling antifouling coating
The corrosive environment of the aluminum alloy ship's bottom and above the waterline is different. The bottom of the ship is mainly the penetration and erosion of natural seawater and the adhesion of aquatic organisms. The above waterline is mainly due to salt spray corrosion and atmospheric aging, therefore, the bottom of the ship The requirements above the waterline for anti-corrosion paints are not exactly the same.
For parts above the waterline, the topcoat should have good resistance to atmospheric aging, good gloss retention, and decorative properties, and be well matched with the primer. Polyurethane finishes and alkyd finishes can be used. Acrylic topcoats, etc., are now commonly used polyurethane finishes. With the continuous improvement of the performance requirements of coatings, fluorocarbon coatings with excellent performance or epoxy- and acrylic-modified fluorocarbon coatings have also begun to be used in the coating systems for aluminum alloys.
Micro-arc oxidation of aluminum alloys
Micro-arc oxidation is a new surface treatment technology that has emerged in recent years. It uses a higher energy density to introduce the anodizing work zone from the Faraday zone to the high-voltage discharge zone. Through the combined action of electrochemical, thermochemical and plasma chemistry, it is used on the surface of non-ferrous metals such as Al, Mg, Ti, and Nd. The formation of a ceramic oxide film.
Prospect of Aluminum Alloy Corrosion Protection Technology for Ships
Aluminum alloy has been widely used due to its various advantages. As the use of aluminum alloy on ships has increased, the corrosion protection requirements for aluminum alloys have become higher and higher.
When arranging the sacrificial anode of the aluminum alloy hull, consideration shall be given to the two different conditions when the ship is docked at the dock and during high-speed navigation. Simulated simulation and optimized layout design shall be adopted. According to the static natural corrosion potential value and dynamic open potential value of aluminum alloys, based on the sacrificial anode material experimental data, quantitative determination of the number of sacrificial anodes, placement location and protection period. At the same time, in different sea areas, sacrificial anode materials that can effectively play a protective role should be used in accordance with the characteristics of the corresponding sea areas.
The surface of the aluminum alloy has special requirements for the coating. Selecting the appropriate coating and formulating the appropriate coating are essential for the anti-corrosion effect of the aluminum alloy ship. With the introduction of environmental protection regulations in succession, anticorrosive coatings for aluminum alloys will adopt new technologies in the future, aiming at non-toxic, universal, and high-performance. The development of new environmentally-friendly, high-performance anti-rust pigments is the focus of future development.
Micro-arc oxidation technology has not entered the stage of large-scale industrial application at home and abroad, but the characteristics of this technology determine that it is more suitable for the protection of the corrosion of the empty tank of aluminum alloy ship. Therefore, in the anti-corrosion field of aluminum alloy ships, micro-arc oxidation technology has a wide range of application prospects.
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