Aluminum alloy has the advantages of small specific gravity, high specific strength, good seawater corrosion resistance, non-magnetic property, good low temperature performance, etc., and it has been paid more and more attention as a structural material in the shipbuilding industry. The use of aluminum alloy as the hull material can effectively reduce the weight of the ship, improve stability and speed, and enhance the technical and tactical performance of the ship. For high-speed planing boats, hydrofoil boats, hovercrafts, small surface boats and some special-purpose vessels, aluminum alloys are particularly suitable. With the development of aluminum alloy inert gas welding technology, the production cost is continuously reduced, the advantages of aluminum alloy materials and the application in the marine environment continue to expand, not only in the field of light ships, but also in the field of high-speed speedboats.
Aluminum and aluminum alloys are very reactive, but because they can form dense and passivated oxide films with oxygen, corrosion resistance is much better than steel. When the aluminum alloy is used on a ship, it is more or less in contact with seawater, or is attacked by seawater droplets and the sea atmosphere, and is subject to certain corrosion. Corrosion of aluminum alloys is a complex process that is both environmentally affected and related to the nature of the alloy. The common types of corrosion of marine aluminum alloys in the marine environment are: pitting, crevice corrosion, intergranular corrosion, exfoliation corrosion and stress corrosion cracking.
The marine environment is a harsh environment, and the anti-corrosion requirements for aluminum alloys in this working environment are higher. For ships, the corrosive environment of different parts is different. The bottom of the ship is mainly affected by the penetration and erosion of natural seawater and the attachment of aquatic organisms. The above waterline is mainly affected by salt spray corrosion and atmospheric aging.
The corrosive environment of the aluminum hull and the waterline is different. The bottom of the ship is mainly the osmotic erosion of natural seawater and the attachment of aquatic organisms. The above waterline is mainly caused by salt spray corrosion and atmospheric aging. Therefore, the bottom of the ship and the water The requirements for anti-corrosive paint on the above line are not exactly the same.
For parts above the waterline, the topcoat should have good weathering resistance, good gloss retention and decorative properties, and good compatibility with the primer. Polyurethane topcoat and alkyd topcoat can be used. Acrylate topcoats, etc., are now commonly used in polyurethane topcoats. With the continuous improvement of coating performance requirements, fluorocarbon coatings with superior performance or epoxy and acrylic modified fluorocarbon coatings have also begun to be applied to the matching coating system of aluminum alloys.
Aluminum alloys have been widely used due to their various advantages. With the increase in the use of aluminum hulls, the anti-corrosion requirements for aluminum alloys are becoming higher and higher.
When the aluminum hull is arranged, consideration should be given to the two different states of the ship docking dock and high-speed navigation. The simulation calculation and optimization layout design should be adopted. According to the static natural corrosion stable potential value and the dynamic open circuit potential value of the aluminum alloy, based on the experimental data of the sacrificial anode material, the number, arrangement position and protection period of the sacrificial anode are quantitatively determined. At the same time, in different sea areas, sacrificial anode materials that can effectively play a protective role should be used for the corresponding sea features.
The surface of the aluminum alloy has special requirements for the coating. Choosing the proper coating and formulating the appropriate matching are essential for the anti-corrosion effect of the aluminum alloy ship. With the introduction of environmental protection regulations, anti-corrosion coatings for aluminum alloys will adopt new technologies in the future, and will develop toward non-toxic, general-purpose and high-performance. The development of new environmentally-friendly and excellent anti-rust pigments is the focus of future development.