Development direction of aluminum alloy materials for high-end ships and marine engineering

Aluminum alloys can be divided into two categories: one is deformed aluminum alloys, which are used for processing semi-finished products such as plates, strips, foils, tubes, bars, shapes, wires, powders, and forgings; the other is cast aluminum alloys, which are used for casting various Castings and Die Castings.

The former is the most widely used in marine engineering. Because aluminum alloy has the characteristics of high specific strength, strong seawater corrosion resistance, weldability, easy processing and forming, strong recyclability, good environmental protection, no low temperature brittleness, no magnetism, and no sparks during magnetic collision, it is widely used in marine engineering. The application can effectively reduce the mass of the ship, improve the stability, increase the speed and so on.

Therefore, aluminum alloys have become one of the main structural materials of ships in many countries in the world, and are widely used in the construction of coastal, lakeside and riverside facilities. Due to the high corrosion resistance of aluminum, it does not need to be painted or maintained, and it can be used for 30 years. The fact that aluminum does not produce sparks when it collides makes it especially suitable for manufacturing ship parts and structures that come into contact with flammable materials and oil, which can greatly reduce the risk of fire.

The Amount of aluminum alloy used on ships

At present, the amount of aluminum used in the manufacture of ships and ships is not much. As far as the world is concerned, the amount in 2013 accounted for about 1.1% of its total consumption. In 2012, the domestic consumption of rolled aluminum in Japan was 974.4kt, of which the transportation consumption was 159.0kt (139.0kt in the automobile industry, accounting for 87.42%, and the domestic consumption of extruded aluminum was 784.5kt, of which the transportation consumption was 141.9kt (131.6 in the automobile industry). kt, accounting for 92.94%), the consumption of these two aluminum materials in the transportation field accounts for 17.11% of the total consumption, while the consumption of the automobile industry accounts for 89.93 of the transportation materials, and the consumption of the aviation industry and marine engineering is less than 10%.

Japan is a country with an underdeveloped aerospace industry, so it is estimated that the consumption of marine engineering will not exceed 5% of the aluminum used in transportation. Japan's aluminum consumption has already entered a stable stage. Since 2004, marine engineering has And the consumption of ships has been hovering around 20kt/a. Among the aluminum materials used, thick plates are the main, accounting for about 88%, and extruded materials are supplemented, but most of the extruded materials are used in coastal facilities.

The aluminum alloy structure for Chinese ships is different from that of Japan. Japan is a big country in the manufacture of LNG (liquefied natural gas) ships. There are four huge LNG tanks welded with 5083 alloy thick plates. The amount of thick plates is about 4kt/ship. China Fe-Ni-Mn steel, which is brittle at low temperature, is used in LNG shipbuilding. In China, only some thick plates are used to manufacture small and medium-sized ships. It is estimated that in 2014, the aluminum used in China's shipbuilding industry was less than 230kt, less than the total apparent consumption of aluminum 1% of the amount.

However, with the acceleration and increase of China's progress towards a maritime power, the amount of aluminum used in ships and marine engineering will increase significantly, but the average annual growth rate before 2025 will not exceed 7.5%.

The Development of Ship Aluminum Alloy

The industrial production of aluminum began with the establishment of the world's first aluminum plant, the Pittsburgh Metallurgical Company in the United States, in 1988. In 1891, the shipbuilding industry used the aluminum produced by the plant to manufacture marine parts for the first time. After more than 120 years of research and development, aluminum The application of materials in ships and marine engineering is more and more extensive, and it has become one of the promising materials in these sectors.

The earliest aluminum alloys used in shipbuilding were Ni-containing Al-Cu alloys, followed by 2XXX series alloys, but their corrosion resistance to seawater was not high, which limited their application in the shipbuilding industry.

The 6061-T6 alloy was used in the 1930s and the hull was constructed by riveting. Corrosion-resistant 5XXX series alloys were welded in the 1940s, and TIG (tungsten inert gas) welding technology was adopted in the 1950s. During this period, the application of aluminum alloys in shipbuilding made great progress. In the 1960s, the U.S. Navy successively developed Al-Mg series 5086-H32 and 5456-H321 alloy sheets, 5086-H111 and 5456-H111 alloy extruded profiles. Due to the use of H116 and H117 states, the intergranular precipitation of Al8Mg5 was eliminated. The compound mesh film solves their problems of exfoliation corrosion and intergranular corrosion, which is a milestone and significant progress in the research and development of ship aluminum alloys since the 1960s.

Subsequently, due to the need for materials with higher yield strength, 6XXX series alloys were widely used in shipbuilding. For a long time, Europe, the United States, Japan and other countries mainly chose 5XXX series alloys and 6XXX series alloys. The hull is made of aluminum alloy, while the Soviet Union prefers 2XXX series alloys. Before the reform and opening up, China's shipbuilding industry mainly followed the Soviet Union. Since 1980, it has followed more countries such as Europe, the United States, and Japan. After 2010, independent innovation has been gradually strengthened. Since the 1970s, the research on medium-strength weldable 7XXX series alloys has been increasing, and some progress has been made, which has been applied in shipbuilding.

Since the 1970s, more and more attention has been paid to the rationalization and weight reduction of ship structures. A large number of aluminum alloys are used in the superstructure and outfitting parts of large ships. To this end, many aluminum alloys and materials for these fields were developed during this period, including extruded profiles of special specifications, large wide extruded panels and castings.