The main application of aluminum alloy in the field of aviation
In aviation equipment, different parts of the aluminum alloy material selection has precise selection requirements. Aluminum alloys used in different parts of the aircraft are mainly 2X24, 7X75, 7X5X, etc. With the continuous improvement of the aluminum alloy material process, the application of grades in different parts of the aircraft is also constantly adjusted.
High-strength aluminum alloy materials in the Boeing 747 airliner is mainly used in the application of 7075T6 and 2024T3 materials more. The main aluminum alloy grades used on Boeing 777 airliners are 7055T77, 7150T77 and 2X24T3; advanced aluminum alloys used on Airbus A380 are 7055/7449/7085/2024/6013/5076 and other alloys, and aluminum alloy materials are used in the lower fuselage wall panels and upper fuselage wall panels, and most of the other ones are carbon fiber composites for weight reduction. Domestic aircraft ARJ21 in the main application of aluminum alloy material grades are mainly 2X24, 7050, 7175, 7075 and so on. Regardless of the proportion of the structure of the material used in the civil aircraft or military aircraft is still mainly aluminum alloy materials, aluminum alloy still has irreplaceable advantages in terms of material cost, process stability, comprehensive mechanical properties and so on.
2 Aluminum alloy applications in the aerospace field
Aluminum alloy in the aerospace field of the launch vehicle on the application of more, the main grade is 7075, 20X4, 2219, etc., the engine device, the main body parts, rotary table, remote control parts, etc., mainly aluminum alloy 7075, such as liquid oxygen tanks are mainly 2219, 20X4 is mainly used in the satellite streamlined outer cover and temperature control valve parts, etc.. In addition, the skeleton of the manned vehicle is made of 2024 and 7075 aluminum alloy, because these two kinds of aluminum alloy have high strength, light quality and thin thickness. Aluminum alloy sheets are also repeatedly used in these objects, such as guards, safety devices, and propellers.
Aerospace Aluminum Alloy Material Process Technology
The final end-use scenarios of aluminum alloys are directly related to the entire production process, and different application scenarios depend on the production process, i.e. the process control of the machining process.
1 Heat treatment process
The comprehensive performance of aluminum alloy materials is enhanced out of the material component ratio, which depends largely on the control of process technology parameters in the production process. Suitable heat treatment methods can greatly affect the comprehensive performance of aluminum alloy materials, so suitable heat treatment technologies should be developed for aluminum alloys with different performance requirements in order to improve the comprehensive performance of aluminum alloy materials.
Adopting high-temperature homogenization annealing process to treat aluminum alloy can make the aging-strengthened phase and residual non-equilibrium phase solidly dissolve into the matrix to the maximum extent, and make them uniformly distributed to improve the concentration of solid solution after solid solution, so as to achieve the effect of aging-strengthening, and at the same time, for the combination of heat treatment process, i.e., heat deformation, intermediate high-temperature homogenization and high-temperature solid solution treatment, for the large aluminum alloy forgings, the parameter design of the whole heat treatment process can improve the strength and increase the strength at the same time. At the same time, the parameters of the whole heat treatment process are designed for the combined heat treatment process of large aluminum alloy forgings, i.e. hot deformation, intermediate high temperature homogenization and high temperature solid solution treatment process, which can improve the stress corrosion performance while improving strength.
Generally the solid solution treatment process of aluminum alloy is divided into 2 kinds: conventional solid solution treatment and compound solid solution treatment, in which the compound solid solution treatment refers to the treatment of enhanced solid solution and high temperature pre-precipitation. The homogenized annealing process of normal temperature treatment + low temperature treatment in the early ingot stage can control the precipitation of transition group elements, which have obvious inhibition effect on recrystallization, and can improve the effect of alloy substructure strengthening to a certain extent, thus improving the fracture toughness of the alloy and stress corrosion resistance and effectively weakening the anisotropy of the material.
High-strength aluminum alloy heat treatment in the aging treatment of aluminum alloy performance also has a crucial role, aging treatment mainly has three forms, peak aging, bipolar aging and regression re-aging. The goal of developing aging treatment is also to make aluminum alloys higher strength, higher toughness, higher corrosion resistance and fatigue resistance and other high comprehensive performance, the development of heat treatment state is along the direction of T6 to T73 to T76 to T736 to T77, the aging treatment is from the development of peak aging to the development of the aging to return to the aging treatment to carry out the sequential development.
The aging temperature and time have influence on the effect of aging strengthening, and different aging treatment process can directly affect the tensile strength, yield strength, elongation and intergranular corrosion grade of aluminum alloy. As early as in 1989, the United States Alcoa company with T77 heat treatment state named registered and declared the first RRA treatment process specification, which is also the first industrial application of heat treatment process specification, this process specification can be used as a 7150 aluminum alloy heat treatment process operation guide, this process of 7150 aluminum alloy plate and extrusion produced by the process has been widely used in the C-17 military transport aircraft. In China, the key technology of high-performance aluminum alloy using T77 heat treatment technology is still in the process of development and has not yet been applied industrially.
Heat treatment process also includes deformation heat treatment, deformation heat treatment is a combination of thermoplastic deformation and heat treatment process, the use of deformation heat treatment can be used to improve the distribution of transition precipitation phase and the fine structure of the internal alloy, reasonable deformation heat treatment can make the aluminum alloy to obtain high toughness and corrosion resistance. The deformation heat treatment process was proposed as early as 1981, mainly applied to the aerospace structural alloys, and the deformation heat treatment has obvious effects on improving the mechanical properties of 7050 and 7475 alloys.
In our country, there are only more than 100 kinds of heat treatment process for aluminum alloy, and there is still a big distance from more than 370 kinds of foreign countries. We should increase the development of heat treatment process and shorten the distance of basic heat treatment technology for aluminum alloy in developed countries.
2 High-strength aluminum alloy extrusion production process
High-strength aluminum alloy in the application process has a variety of forms, mainly in the form of aluminum profiles, aluminum plates, 3D printing powder and so on. Among them, aluminum alloy profiles have excellent characteristics such as light weight and high strength, mature welding process, etc. Aluminum profiles can be used as large-scale structural load-bearing parts in the aerospace and rail transportation fields in a large number of applications. The production process of aluminum profiles mainly adopts continuous pultrusion molding process to improve the production efficiency and certain pre-stress orientation to improve the mechanical properties of profiles. In the extrusion process of aluminum profiles, in the continuous extrusion method of multiple extrusion cycles, an interface will be formed between 2 adjacent extruded billets, which increases the extension length of the interface in the profile, because the transverse weld will greatly affect the service life of the aluminum profile, resulting in a sharp decline in fatigue life.
3 High-strength aluminum alloy 3D printing process
The development of low-cost, high-efficiency and automated high-strength aluminum alloy process technology has been the attention of aerospace, large-scale aluminum alloy or titanium alloy 3D printing technology for the current focus of aerospace attention. 3D printing technology, as a forward-looking strategic technology in our country, has a vital role in the development of engineering applications.
In the field of aerospace, although there have been a large number of applications of aluminum alloys, but the actual application process compared to titanium alloys and composite materials there are certain disadvantages, such as aluminum alloys exposed to higher than 160 ℃ in the application of mechanical properties and corrosion resistance, fatigue performance will be reduced, and with the prolongation of the use of time will be softened and aging, so to enhance the comprehensive performance of aluminum alloys in the extreme working conditions still need to carry out a lot of work.
Through the continuous maturation of 3D printing technology, the development of high-strength aluminum alloy powder is also ongoing, and new aluminum alloy materials continue to emerge and continue to refresh the performance of new highs. Aluminum alloy 3D printing development prospects are promising, mainly used in aerospace and military fields.
