Abstract: at present, China has taken three key steps in the general aircraft manufacturing industry, namely, the regional airliner ARJ21-700, the single-aisle jet C919 and the dual-aisle jetliner C929. Aluminum parts of ARJ21-700 aircraft are mostly made of hard aluminum alloy such as aluminum-copper alloy and aluminum-zinc alloy, but aluminum-lithium alloy has not been applied.
Aluminum alloy has the advantages of light weight, high specific strength and corrosion resistance. since the engine crank box made of aluminum alloy was used in the world's first aircraft manufactured by the Wright brothers in 1903, aluminum alloy has developed continuously with the progress of the aviation industry. Lithium is the lightest metal element. With every 1% increase of lithium in aluminum alloy, the density of aluminum alloy can be reduced by 3% and the modulus can be increased by 6%. In addition to the above advantages, Al-Li alloy material can also greatly improve fatigue resistance and low temperature toughness. Therefore, Al-Li alloy has become an important aviation material in many countries.
01. Present situation of production and application of Al-Li alloy at home and abroad.
The research and development of Al-Li alloy has gone through three stages, the first generation is represented by 2020 and BA alloy 23, and the second generation is represented by 1420 and 2090. At present, it has been developed to the third generation Al-Li alloy, which has good comprehensive properties. The newly developed and improved Al-Li alloys such as 1460, 2198, 2199 and 2050 are widely used in advanced large airliners and spacecraft. In order to meet the needs of the aerospace industry, large aluminum companies and scientific research institutions in the world have begun to develop the fourth generation Al-Li alloy. Compared with the third generation, the lithium content of the new generation Al-Li alloy will be reduced, while the strength and fracture toughness will be improved. The elongation has decreased, and other properties can still reach or even exceed the level of the third generation Al-Li alloy.
1.1 present situation of production and application abroad.
At present, the foreign countries with complete Al-Li alloy production system are mainly distributed in five developed regions, namely, the United States, Russia, Britain, France and Italy. The total production capacity of Al-Li alloy is about 200000 t. These countries have established a complete smelting-casting-processing system, in which smelting-casting is a key process for the production of Al-Li alloy materials.
The United States is in the forefront of the world in the research and development, production and application of aluminum-lithium alloys, accounting for about 50% of the world's production capacity. The types of products cover plate, strip, extruded materials, bars, wires and forgings, such as Weldalite, AIRWARE, 2099, 7055 and so on. The main production enterprises are Okonink Aluminum Co., Ltd., Kenlian Aluminum Co., Ltd., Aili Aluminum Co., Ltd. Okonink Aluminum Co., Ltd. is the world's largest aluminum-lithium alloy manufacturer, with a production capacity of about 55000 t. Okonink's production capacity is mainly distributed in Davenport Rolling Plant, Lafayette forging and Extrusion Plant, Longway Aluminum Company, British Kitzgreen Aluminum Company, Italy Fusina Aluminum Company and Changyuan Extrusion Plant in South Korea. The main customers include Boeing, Airbus, Lockheed Martin, Gulfstream Aerospace, Comac and many other large civil and military aircraft manufacturers.
Kenlian Aluminium's aluminum-lithium alloy production is completed in the Isual rolling mill in France, with a production capacity of about 14000 t. Its main customers are European Aerospace, Airbus and Bombardier. Eli Aluminium's Al-Li alloy production is located in the Koblenz plant in Germany. In the 1950s, the United States used the earliest industrial aluminum-lithium alloy 2020 on RA-5C early warning aircraft, which reduced the total weight of the aircraft by 6%. After the 1990s, the third-generation aluminum-lithium alloy was used in the rear partition frame of FMui 16, the beam of Boeing 787 and the outer storage box of the space shuttle Endeavour, and achieved good weight loss results. The Cmur17 transport plane uses 2.8t Al-Li alloy plates and extruded profiles to make the floor beam and flap aileron skin of the cargo hold, which is 208kg less than that of ordinary aluminum alloy.
The R & D, production and application of Russian Al-Li alloy began in the former Soviet Union, and it is the second largest country in R & D, production and application in the world after the United States; its production capacity accounts for about 25% of the world, and the type of processing materials is similar to that of the United States. Representative alloys are 1420, 1450, 1460 and so on. The production enterprises are mainly Ural Kamensk Aluminum Co., Ltd., and the market is mainly for the domestic aerospace sector. In the early 1970s, 1420 Al-Li alloy was used in the fuselage, fuel tank, cockpit and other parts of MiG-29, and the weight reduction effect reached 24%. When it comes to the third generation of Al-Li alloy, Russia also uses the new Al-Li alloy in the liquid hydrogen tank of the Space Shuttle Blizzard, MiG-29, Su-27, Tu-144 and other civil and military aircraft. For example, the amount of Al-Li alloy per MiG-29 aircraft accounts for 3% of the total weight of the fuselage.
The research and development, production and application of Al-Li alloy in Europe are distributed in Britain, France and Italy. These countries have lagged behind the United States and Russia in the research and development of the third generation Al-Li alloy, and the production is carried out by the European plants of American companies. For example, the former French Puji Aluminum Company has been merged into the Kenlian Aluminum Company of the United States. The Kitzgreen Rolling Mill in the UK and the Fusina Rolling Mill in Italy are all part of the Okonink Aluminum Company of the United States. Users include Airbus, Agusta Westland, Eurofighter and so on. All the thin plate-like parts in the front of the Typhoon fighter are made of 8090 aluminum-lithium alloy thin plates, accounting for 9% of all materials. The cover of the electronic equipment room in the cockpit is 1.5m long. The fuselage frame, skin and internal structure of EH101 helicopter are widely used aluminum-lithium alloy plates and forgings, and the weight of each aircraft is reduced by 200kg.
1.2 present situation of domestic production and application.
In China, in order to meet the demand of domestic aircraft for Al-Li alloy, China's aluminum processing industry began to study the tracking of Al-Li alloy in the 1960s, and successfully imitated 8090 and 2091 Al-Li alloy. During the eighth five-year Plan period, China has been able to cast 1t Al-Li alloy and initially has the ability to produce small-size Al-Li alloy plates and profiles. During the Ninth five-year Plan period, through the introduction of a 6t vacuum melting furnace and casting equipment and technology for Al-Li alloy in Russia, a great leap from 1t to 6t was achieved in the melting and casting of Al-Li alloy. In 2012, Southwest Aluminum broke through many key technologies of the third generation Al-Li alloy and realized the coordinated improvement of the comprehensive properties of Al-Li alloy.
After nearly 40 years of research and exploration, China has basically mastered the melting technology of aerospace Al-Li alloy materials, such as the casting technology of Al-Li alloy large flat ingots and Al-Li alloy round ingots. However, there is still a big gap between the basic research and industrial production and application of Al-Li alloy with the United States and Russia. At present, only Southwest Aluminum (Group) Co., Ltd. can produce a small amount of Al-Li alloy with an annual output of less than 100t, which is far from being able to meet the needs of domestic large aircraft.
02. Forecast of domestic market demand for Al-Li alloy.
Al-Li alloy has been used in military aircraft, civil airliners, helicopters and spacecraft, mainly used in fuselage frame, flap rib, vertical stability surface, fairing, inlet lip, hatch, fuel tank and so on. In the design and manufacture of new aircraft, light weight and weight loss are often calculated in the aviation field. The use of Al-Li alloy can reduce the mass of aircraft aluminum alloy parts by 14% to 30%. The effect of weight reduction is that the annual flight cost of each aircraft will be reduced by more than 2.2%, so Al-Li alloy is considered to be the most ideal structural material for aerospace.
At present, China has taken three key steps in the general aircraft manufacturing industry, namely, the regional airliner ARJ21-700, the single-aisle jet C919 and the dual-aisle jetliner C929. Aluminum parts of ARJ21-700 aircraft are mostly made of hard aluminum alloy such as aluminum-copper alloy and aluminum-zinc alloy, but aluminum-lithium alloy has not been applied. The third generation Al-Li alloy is used in the fuselage skin, long truss, floor beam, slide rail, boundary beam, floor support structure and other parts of the C919 aircraft. The Al-Li alloy material of the whole aircraft accounts for 15.5%, with a dosage of 14t, and a good effect of comprehensive weight reduction of 7% has been achieved.
Aluminum-lithium alloy plates are widely used in the straight section of the C919 fuselage made by Hongdu and the large parts of the fuselage and aileron of the C919 made in Xi'an, but the third-generation aluminum-lithium alloy used in the C919 aircraft comes from Okonink Aluminum Co., Ltd. In June 2018, the overall shape and size of the C929 long-range wide-body airliner were formally determined, and the preliminary design (G3) work is being carried out. It is certain that the third-or even fourth-generation aluminum-lithium alloy will be widely used in C929 aluminum parts in the future.
According to the 2017 Statistical report on the Development of Civil Aviation Industry released by the Civil Aviation Administration of China, in 2017, the total transport turnover of China's civil aviation industry was 108.308 billion ton / km, an increase of 12.6 percent over the previous year, and the total transport turnover of the whole industry increased at an average annual rate of 12.2 percent in the past five years. By the end of 2017, the number of transport aircraft in the civil aviation industry at the end of the period was 3296, an increase of 346 over the end of last year. According to the 13th five-year Plan for the Development of China's Civil Aviation issued in December 2016, it is estimated that by 2020, the total air transport turnover of the country's civil aviation industry will reach 142 billion ton / km, with an average annual growth rate of 10.8%. The number of civil aviation general-purpose aircraft has reached more than 5000.
At the same time, it is planned and proposed that during the 13th five-year Plan period, it is necessary to do a good job in the post-certification management of ARJ21-700 aircraft and Xinzhou 60 series aircraft, and carry out the examination and approval of domestic large airliner C919 aircraft and other models. In addition, according to the Commercial aircraft Market Forecast Annual report of Comac of China from 2017 to 2036 released by Comac in September 2017, China is expected to deliver 8575 passenger aircraft worth about US $1.2104 trillion in the next 20 years, with an average annual demand of more than 420 aircraft. Among them, single-aisle jetliners accounted for 64%, a total of 5475, dual-aisle jetliners accounted for 23%, a total of 2003, and regional jets accounted for 13%, a total of 1097.
In recent years, China's economy has developed rapidly and consumption has been gradually upgraded. In 2017, China's annual per capita GDP was 8836 US dollars, which has entered the level of upper-middle-income countries. The demand for aviation consumption continues to rise. The per capita number of flights in China is close to 0.4 times per year, double that of 10 years ago, but compared with developed countries such as the United States (2.7times / year), the United Kingdom (2.1times / year) and Japan (0.9times / year). The gap is obvious. According to the planning of the Civil Aviation Administration, the per capita number of flights in China will reach 0.5 times per year in 2020 and 1.04 times per year by 2030. It can be seen that the improvement of China's air transport industry provides a huge market space for the demand for aircraft.
At present, the domestic single-aisle C919 jetliner C919 has received 730 orders, and the first C919 is expected to be put into commercial use in 2021. If these orders are all made in China, the Al-Li alloy usage refers to the current C919 level, and considering that the amount of Al-Li alloy used in each aircraft is 14t, only the single-aisle C919 aircraft needs Al-Li alloy 10220t, coupled with the dual-aisle C929 aircraft already under development, the demand for Al-Li alloy is more than 20000t. According to the forecast of Comac of China, China will need 7478 single-aisle and dual-aisle aircraft in the next 20 years. If the 1max-3 aircraft is produced by Comac of China and competes with Boeing and Airbus, the domestic demand for aluminum-lithium alloy will be more than 30000 tons.
In addition to a large number of applications in civil aircraft, another major application market of Al-Li alloy is military aircraft. According to statistics, in 2017, the number of China's military combat aircraft reached 1453, mainly second-and third-generation combat aircraft, accounting for 10 percent of the world, only half of that of the United States, ranking second. With the improvement of China's national strength, the state has continuously increased its investment in the aerospace industry in order to alleviate the pressure of land transportation, protect homeland security and overseas interests. During the 13th five-year Plan period, the Chinese Air Force will usher in the peak period of "three-and-a-half" fighters, including J-10C, J-11D, J-16 and Su-35SK. The scale of "three-and-a-half" fighters will rank second in the world, and the production capacity of these tactical aircraft is expected to exceed 115s per year. And the fourth-generation fighter J-20 and J-31 have already been put into service, coupled with the production capacity of about 10 strategic aircraft per year, it has become the country with the highest output of military aircraft in the world, and this situation will not change greatly in the next decade.
If produced at this rate, China's military aircraft will need nearly 500 tons of aluminum-lithium alloy per year. Al-Li alloy can be used to manufacture space shuttle fuel tank, rocket fuel tank and space station structure in the aerospace field. To sum up, in the next ten years, the average annual demand of domestic civil and military aircraft will reach about 550, and the annual demand of Al-Li alloy will be more than 1500t.
03. Forecast and suggestion on market supply of Al-Li alloy.
At present, domestic colleges and universities such as Central South University and Beijing Institute of Aeronautical Materials have carried out basic research on Al-Li alloy. Only Southwest Aluminum can produce Al-Li alloy, and the output is very low, less than 100 tons. The Al-Li alloy needed for large aircraft still needs to be imported from the United States, while the annual demand for Al-Li alloy for domestic military and civil aircraft reaches 1,500 tons, which is more than 15 times the production capacity. There is an urgent need for industrialization of Al-Li alloy materials.
In the future, China should take the demand of Al-Li alloy in large aircraft, rockets and other advanced aeronautics and spacecraft as an opportunity to strengthen the research, production and application of the third generation or more advanced Al-Li alloy materials, so as to improve the ability of independent innovation and localization. Therefore, it is suggested that the state and related enterprises should continue to provide policy support and invest special funds, increase the number of research and production entities, strengthen and upgrade the construction of research and production, application platforms and tooling equipment, promote joint development and collaborative promotion of R & D, production and application enterprises, enhance Al-Li alloy R & D and innovation capabilities and achievement transformation capabilities, upgrade and expand aerospace Al-Li alloy production lines.