China's aircraft aluminum technology behind Russia and the United States for 30 years

A Comparison of Development of Aviation Aluminum in China and Foreign Countries

Due to its unique advantages such as low density, moderate strength, easy processing and forming, strong corrosion resistance, abundant resources, and high recyclability, aluminum alloys have been developing with aluminum alloy materials since 1903. The application has formed an indissoluble bond. Although the proportion of composite materials represented by carbon fiber-reinforced plastics has increased in recent years, the cost-effective aluminum alloy still occupies an absolute advantage and remains the key structural material for aircraft manufacturing. In the materials of regional jets ARJ21-700 and C919 passenger planes with independent intellectual property rights in China, the quality of aluminum alloy components accounts for 68% to 75% of the total mass of the aircraft. From the perspective of development history, aluminum alloy materials and the aviation industry have always complement each other, and both upgrade and mutual promotion. The birth of a new type of aluminum alloy has created a new generation of aircraft manufacturing. The higher performance aircraft has also promoted the development and application of a new generation of aluminum alloys. With respect to the development of civil aircraft, the high-strength deformed aluminum alloy was adapted to the Boeing 707 in the 1950s, and the 7085 aluminum-lithium alloy corresponds to the current Airbus A380. From the point of view of the global aluminum processing industry and the aviation industry, the use of deformed aluminum alloys is quite mature. At present, the demand for new aircraft materials is mainly reflected in aluminum-lithium alloys with better overall performance.

Development of aluminum-lithium alloys for aviation civil aircraft

The aluminum-lithium alloy is aerospace 7085 aluminum alloy newly developed by Alcoa in 1983. It was registered with the Aluminum Association of America in 2002 and is used to produce 102-178mm aircraft thick plates. Al-Li alloy is an unprecedented ultrapure 7xxx series alloy. Lithium has a large chemical activity. Therefore, the aluminum-lithium alloy must be smelted in a vacuum furnace, and the melt must also be cast under a protective atmosphere. The smelting process is the most critical technique for producing aluminum-lithium alloys. Lithium can both reduce the density of aluminum and increase the modulus of elasticity. For every 1% of lithium added to aluminum, the density of the aluminum alloy drops by about 3%, and its elastic modulus increases by about 6%, making it a strong competitor for composites (carbon fiber reinforced plastics). According to tests conducted by Boeing Aircraft, the use of aluminum-lithium alloy Boeing aircraft, its weight can be reduced by 14.6%, fuel savings of 5.4%, aircraft manufacturing costs can be reduced by 2.1%, each aircraft's annual flight costs can be reduced by 2.2%. Since the cost of Al-Li alloys is only about 10% of that of composite materials (carbon fiber-reinforced plastics), there is a clear comparative advantage in application. In 2009, aluminum-lithium alloys were incorporated into the United States Aerospace Materials Standard. At present, the third-generation aluminum-lithium alloys have achieved large-scale industrial production, and the fourth-generation lithium-lithium alloys have achieved new results. In the new aircraft design and manufacturing, the use of aluminum-lithium alloy can reduce the quality of aircraft aluminum parts by 14% to 30%, has become the key structural material of the new generation of aircraft.

The new focus of aviation aluminum alloys is the development and application of advanced aluminum lithium alloys. According to statistics, Alcoa is the world's largest manufacturer of aluminum-lithium alloys with production capacity and production volume, accounting for approximately 55% of the world's total. Russia’s United Aluminum Corporation accounts for approximately 25%, and other companies account for approximately 20% of the total. At present, there are seven plants in the world that can produce aluminum-lithium alloy rolling materials, 11 factories can produce aluminum-lithium alloy extrusion materials, and nine factories can forge aluminum-lithium alloy free forgings and die forgings, including our country's southwest Aluminum (Group) Co., Ltd.

Although Alcoa’s production of aluminum-lithium alloys ranks first in the world, Al-Li alloys are still being expanded. For example, Alcoa established the world's largest aluminum-lithium alloy production plant in Lafayette and will supply third-generation aluminum-lithium alloy parts to aircraft manufacturers such as the Airbus A380, A350 and Boeing 787.

In mid-2013, Alcoa completed the expansion of aluminum-lithium alloy production capacity at the Kitts Green plant in the United Kingdom; the aluminum-lithium alloy plate production line at the Davenport rolling mill was rebuilt and expanded; and Lafayette, Annapolis, India Extrusion—The aluminum-lithium alloy production line of the forging plant has been expanded. According to the statistics at the end of 2013, the production capacity of aluminum-lithium alloys in the United States is approximately 100,000 tons/year, of which Alcoa's production capacity is approximately 55,000 tons/year, and Alcoa's aluminum-lithium alloy production capacity accounts for 55% of the country's total.

Since the birth of aluminum-lithium alloy, the alloy has been in the process of refinement and refinement, and a new generation of aluminum-lithium alloy with lighter weight, higher strength, and lower cost has been continuously developed, such as the third-generation aluminum lithium of Alcoa Corporation. Alloy has achieved large-scale industrial production. The United States Ken Lian Aluminum Company's Wreep R&D center in France spent 10 years developing a new type of aluminum-lithium alloy called “AIRWARE”, which is a revolutionary new aluminum alloy material used in the aerospace field. . It fuses aluminum with other metals such as lithium, copper, and silver to obtain this new alloy.

It is understood that AIRWARE can bring four major advantages to aircraft manufacturing: First, it is 25% lighter than traditional aluminum alloy materials. Therefore, it can optimize the design of structural components and reduce carbon dioxide emissions. Second, it is excellent in corrosion resistance and resistance to metal. The fatigue characteristics can be extended to a larger maintenance interval of up to 12 years. Third, 100% recycling can be achieved. The fourth is that it can be used to manufacture all parts of an aircraft. At present, AIRWARE has been applied in the manufacture of a new generation of aircraft. Airbus applied it to its wide-body passenger aircraft A350-XWB; Bombardier applied it to the narrow-body aircraft C series. In order to meet the growing demand for new aluminum-lithium alloys in the aviation market, Kenlian Aluminum is currently constructing two new aluminum-lithium alloy melting and casting production lines at the rolling mill in Issoire, France, specializing in the production of AIRWARE aluminum-lithium alloys. Two production lines are under construction. Will be put into production before 2016.

In China, in order to meet the demand for aluminum-lithium alloys made by domestic aircraft, aluminum processing companies in China began tracking aluminum-lithium alloys in the 1960s. There are two types of imitation aluminum-lithium alloys: the first is the 8090 alloy (1984 The alloy invented by the European Aluminum Association); the other is the 2091 alloy (invented in 1985 by the French alloy). The performance of the two domestic aluminum-lithium alloys has reached the level of foreign countries. In 2000, SWA introduced aluminum-lithium alloy vacuum melting furnace and casting equipment from the Moscow Light Metal Research Institute in Russia. China can produce aluminum-lithium alloy plates, sections and forgings in small batches. In January 2012, SWA successfully piloted a third-generation aluminum-lithium alloy for use in domestic large aircraft projects.

At present, China has basically mastered the smelting technology of aviation aluminum-lithium alloys, such as aluminum-lithium alloy slabs and aluminum-lithium alloy ingot casting techniques, but in the basic research of aluminum-lithium alloys and alloy production practices, with Russia, the United States should There is a big gap between 20 and 30 years. The main manifestations are as follows: First, the capacity for innovation and technology development is relatively weak; second, the production capacity is small. At present, only the southwestern aluminum can produce aluminum-lithium alloys, and the annual output is still very small.

China's large aircraft manufacturing and application of aluminum alloy materials

In China, the demand for large aircraft manufacturing is driving the demand for aluminum alloy materials, especially aluminum-lithium alloy materials. China's large aircraft C919 airliner fuselage and other straight sections, including the front passenger cabin, front cargo compartment and recirculation fan cabin, is a tubular structure section consisting of skins, cabin portholes, cabin floors, and load-bearing components. It is understood that the C919 fuselage and other straight sections are located in the front of the fuselage, which is a section of tubular structure with equal width. It is 7.45 meters in length, 4.2 meters in width and 4.2 meters in height. It adopts advanced third-generation aluminum lithium. Alloy plate, this is the first time that China's civil aircraft has been manufactured using aluminum-lithium alloys.

In September 2014, the mid-airframe and outer wing components of the C919 large passenger aircraft were delivered. The main parts of the mid-airframe and outer wing boxes delivered for the first time were 5.99 meters long and 3.96 meters wide. The mid-fuselage barrel section, the keel beam, and the central wing , Emergency door composition, the section contains more than 8,200 parts, involving more than 3400 tooling, a large number of third-generation aluminum lithium alloy and high damage tolerance aluminum alloy material.

At present, the C919 large passenger aircraft has received 507 orders from over 20 domestic and foreign airlines, and the ARJ21-700 has 278 orders. According to the plan, by 2018, domestic aluminium will be used for more than 30% of aluminum alloy materials used in the ARJ21 regional airliner and the C919 large aircraft. The demand for aluminum alloy materials from China’s large aircraft has increased the urgency of aluminum alloy R&D and large-scale production of aviation civil aircraft in China’s aluminum processing companies.

At present, the aluminum alloy materials used in aviation civil aircraft mainly include: aluminum alloy castings, aluminum alloy forgings, large section aluminum alloy extruded profiles, aluminum alloy thick plates, and aluminum-lithium alloys. After more than 60 years of development, China's aluminum processing industry has become an internationally recognized leader in the production of aluminum materials. At present, whether it is aluminum alloy melting equipment, rolling equipment, or aluminum alloy extrusion equipment and finishing equipment, modern aluminum processing equipment The number of countries should be the largest in the world, but due to low investment in research and development, weak basic research, and modern first-rate equipment can only mass produce aluminum materials with low performance, such as high-end aluminum used in the aerospace industry or ours. Short board.

Since China had a modernized aluminum processing industry in 1956, the aviation aluminum alloy thick plates required have been in a net import state. In the initial domestic ARJ21-700 regional airliner and large passenger aircraft C919 materials, aluminum and aluminum alloy forgings were imported from Alcoa or provided by its wholly-owned enterprises in China. Nowadays, the aluminum-lithium alloys with strong demand from the aviation industry are still at the stage of follow-up imitation research and development. There are still many difficulties to achieve large-scale commercial production, and there is still a long way to go.

It is an indisputable fact that China’s aviation civil aircraft, especially the domestic C919 and ARJ21 large aircrafts, have developed rapidly. It is time for aviation aluminum development to take a long way to go! China's aluminum processing industry has the world's leading modern aluminum processing technology and equipment, as long as the advantages of modern aluminum processing equipment to take advantage of advanced foreign countries and their counterparts to carry out technical cooperation and absorb their work Experience and R&D results will surely achieve "turning overtaking."