A sea ranch is a platform that floats on offshore waters to artificially breed marine life. On April 10 this year, the main platform of the second phase of the marine ranch project “Genghai 1” successfully launched in Yantai City, Shandong Province. Subsequently, the tilt test was completed. The “Genghai No. 1” marine ranch complex platform, positioned in the sea east of Fisherman’s Wharf in Yantai City, Shandong Province, seamlessly combines fishery farming, maritime tourism, technology research and development, and other functionalities. It leverages technological innovation to enhance fishery farming efficiency and achieve an upgrade in marine fishery. Reports indicate that “Genghai No. 1” features an advanced design and includes automatic feeding, environmental monitoring, ship anti-collision systems, unmanned ships, underwater inspection robots, and other technical equipment. This configuration enables intelligent control of the entire production process.
More than 75% of the superstructure and internal structures in marine ranch construction are crafted from aluminum among the metal materials employed. Because aluminum has a low density, it can greatly reduce the quality of the structure itself. At the same time, aluminum has a strong impact on seawater and ocean atmosphere.When considering corrosion resistance, one could argue that the marine ranch ought to use all-aluminum materials. The term “all-aluminum” doesn’t mean crafting every structural component from aluminum or its alloy. Instead, it suggests that all components feasible for aluminum or its alloy should be manufactured accordingly, while meeting technical specifications and ensuring safety and environmental standards.
The corrosion of aluminum alloys is more serious than that of pure aluminum, but there are a few exceptions.
The corrosion resistance of aluminum and its alloys in air, acid, and water follows a descending order: Al, Al-Mn alloy, Al-Mg alloy, Al-Mg-Si alloy, Al-Si alloy, Al-Zn-Mg alloy, Al-Zn-Mg-Cu alloy, Al-Cu-Mg alloy, Al-Cu alloy. Similarly, in alkaline solution and seawater, the descending order is: Al-Mg alloy, Al, Al-Mn alloy, Al-Mg-Si alloy, Al-Zn-Mg alloy, Al-Si alloy, Al-Zn-Cu-Mg alloy, Al-Cu-Mg alloy, Al-Cu alloy. It’s essential to note that this corrosion resistance ranking applies only when alloys susceptible to exfoliation corrosion, intergranular corrosion, or stress corrosion cracking have undergone heat treatment to eliminate these sensitivities.
Moreover, this ranking serves as a general guideline, subject to potential variations in special circumstances. The corrosion resistance of aluminum-clad materials is only slightly worse than that of aluminum-clad materials. For example, the corrosion resistance of AI-Cu alloy coated with pure aluminum is equal to or even better than that of AI-Mn alloy.
Clearly, Al-Mg series alloys, particularly the 5XXX (5000) series aluminum alloys, stand out as the prime choice for crafting marine equipment. This preference arises from their outstanding resistance to corrosion in marine environments and their lower density compared to other aluminum alloys. Such characteristics are highly advantageous for reducing the weight of products like the “Genghai No. 1” marine ranch complex platform. Thanks to the high corrosion resistance of the Al-Mg system, aluminum alloy platforms necessitate no maintenance throughout their life cycle (30 years). In contrast, steel platforms would require maintenance every three to five years to prevent rust accumulation.
Among the 105 commonly used AI-Mg alloys registered by the American Aluminum Association (AA), 5182, 5454, 5083, 5086, and 5052 alloys have the best overall properties. My country currently boasts the capability to mass-produce the aluminum alloys essential for manufacturing such marine equipment. These alloys are produced with high quality standards and are available at reasonable prices.
