Material selection principles and advantages of aluminum alloys for ships

Material selection principles and advantages of aluminum alloys for ships

High specific strength and specific modulus

The yield strength and elastic modulus of materials are the most basic parameters for calculating the strength of ship structures and determining the structural dimensions. Since the elastic modulus and density of various aluminum alloys are roughly the same, and adding a small amount of alloying elements or changing the heat treatment state has little effect on them, increasing the yield strength within a certain range is beneficial to reducing the weight of ship structures. Generally, the density of aluminum alloys is about 2.7~2.8/cm3, and the elastic modulus is about 70~73GPa. However, it is usually difficult for high-strength aluminum alloys to have excellent corrosion resistance and weldability at the same time. Therefore, aluminum alloys for ships are generally selected from aluminum alloys with medium strength and corrosion resistance and weldability. In addition, cast aluminum alloys also have certain applications in the field of ships.

Material selection principles and advantages of aluminum alloys for ships

Excellent welding performance

For ships, welding connection has obvious advantages over riveting connection. Therefore, welding connection method has been widely used in shipbuilding, basically replacing riveting structure. At present, automatic argon arc welding method is mainly used in aluminum ship construction. The good weldability of aluminum alloy means that the tendency of cracks formed during welding of aluminum alloy is small, that is, aluminum alloy has good welding crack resistance, and the performance of welded joints does not change much after welding. Because the performance lost due to welding cannot be restored by re-heat treatment under shipbuilding conditions, this is one of the important characteristics of marine aluminum alloys that is different from other structural aluminum alloys. The strength of AL-Zn-Mg and AL-Mg-Si alloys is significantly reduced after welding, and the corrosion resistance of AL-Zn-Mg alloys is also poor after welding. Therefore, these two alloys are subject to certain restrictions when used as welding ship materials. AL-Mg alloys do not have this disadvantage. AL-Zn-Mg alloys are mainly used for components that can be heat treated after welding (such as torpedo shells), and AL-Mg-Si alloys are mainly used as profiles.

Excellent corrosion resistance

Ship structures are mostly used in harsh seawater media and marine environments, so whether aluminum alloys are corrosion-resistant is one of the main indicators that determine whether they can be used as marine aluminum alloys. Generally, it is required that the marine aluminum alloy matrix and welded joints have no tendency to stress corrosion, exfoliation corrosion and intergranular corrosion in seawater and marine environments; contact corrosion, crevice corrosion and marine biological attachment corrosion should be avoided as much as possible; and small uniform corrosion and pitting corrosion are allowed.

Good cold and hot forming performance

During the construction process, ships must undergo cold processing (such as folding, curling, roll bending, stamping, etc.) and hot processing (such as hot bending, pyrotechnic correction, etc.). Therefore, marine aluminum alloys are required to be easy to process and form, without defects such as cracks during processing, and still meet the performance requirements of strength and corrosion resistance after processing.

Advantages of aluminum alloy in ship applications

Aluminum alloy has the characteristics of low specific gravity and elastic modulus, corrosion resistance, weldability, easy processing, non-magnetic and good low-temperature performance. It has the following advantages when used in ships:

• (1) Due to its low specific gravity, it can reduce the weight of the ship, reduce the capacity of the engine, and increase the speed; it can reduce fuel consumption and save fuel; it can improve the length-to-width ratio of the ship, increase stability, and make the ship easier to operate; it can also increase the load capacity and obtain additional profits.
• (2) Due to its good corrosion resistance, it can reduce maintenance costs such as oiling and extend the service life (usually more than 20 years).
• (3) It has good processing and forming performance and is easy to perform various forms of processing such as cutting, stamping, cold bending, forming and cutting, which is suitable for the streamlining of the hull; it can extrude large wide and thin-walled profiles, reduce the number of welds and make the hull structure more rational and lightweight.
• (4) It has good welding performance and can be welded more easily.
• (5) It has a small elastic modulus, a large ability to absorb impact stress, and greater safety.
• (6) Aluminum waste is easy to recycle and can be reused.
• (7) It is not brittle at low temperatures and is most suitable for low-temperature equipment.
• (8) Since it is non-magnetic, the compass is not affected; all-aluminum ships can avoid mine attacks and are suitable for minesweepers.
• (9) It is free of insect pests and dry deformation; it does not burn and is safer in case of fire.

More knowledge about marine aluminum plates: https://hw-alu.com/applications/aluminum-sheet-for-boat.html