Aviation aluminum alloy material technology
The final use scenario of aluminum alloy is directly related to the entire production process, and different application scenarios depend on the process control of the production process, that is, the processing process.
01, high strength aluminum alloy extrusion profile production process
High-strength aluminum alloy has a variety of forms in the application process, mainly aluminum profiles, aluminum plates, 3D printing powder and other forms. Among them, aluminum alloy profiles have excellent characteristics such as light weight, high strength and mature welding process. Aluminum profiles can be widely used as large structural bearing parts in aerospace and rail transit fields. The production process of aluminum profiles mainly adopts continuous pultrusion molding process to improve production efficiency and prestress orientation to improve the mechanical properties of profiles. In the extrusion process of aluminum profiles, in the continuous extrusion method with multiple extrusion cycles, an interface will be formed between the adjacent two extrusion billets, making the extension length of the interface in the profile increase, because the transverse weld will greatly affect the service life of aluminum profiles, resulting in a sharp decline in fatigue life.
02, heat treatment process
The comprehensive performance of aluminum alloy materials to improve the material composition ratio, to a large extent depends on the process technical parameters in the production process control, the appropriate heat treatment method can greatly affect the comprehensive performance of aluminum alloy materials, so for different performance requirements of aluminum alloy should be developed suitable heat treatment technology to improve the comprehensive performance of aluminum alloy materials.
Using high temperature homogenizing annealing process to treat aluminum alloy, the aging strengthening phase and residual non-equilibrium phase can be solidly dissolved into the matrix to the maximum extent, and their uniform distribution can increase the concentration of solid solution after solid solution, and achieve the effect of improving aging strengthening. At the same time, according to the combined heat treatment process of large aluminum alloy forgings, namely hot deformation, intermediate high temperature homogenization and high temperature solution treatment process, the whole heat treatment process parameter design can improve the strength and improve the stress corrosion performance.
General aluminum alloy solid solution treatment process is divided into two kinds: conventional solid solution treatment and composite solid solution treatment, of which composite solid solution treatment refers to the strengthening of solid solution and high temperature pre-precipitation treatment. In the early ingot casting stage, the homogenization annealing process of normal temperature treatment and low temperature treatment can control the precipitation of transition elements, and the transition elements have obvious inhibition effect on recrystallization, which can improve the substructure strengthening effect of the alloy to a certain extent, and then improve the fracture toughness and stress corrosion resistance of the alloy, and effectively weaken the anisotropy of the material.
The aging treatment in the heat treatment of high-strength aluminum alloy also plays a crucial role in the performance of aluminum alloy, and there are three main forms of aging treatment, peak aging, bipolar aging and regression reaging. The goal of the development of aging treatment is to make the aluminum alloy higher strength, higher toughness, higher corrosion resistance and fatigue resistance and other high comprehensive properties, heat treatment state development is along the direction of T6 to T73 to T76 to T736 to T77, aging treatment is from the peak aging development to over-aging and then to the return of re-aging treatment for sequential development.
Aging temperature and time have influence on the effect of aging strengthening. Different aging treatment processes can directly affect the tensile strength, yield strength, elongation and intergranular corrosion grade of aluminum alloy. As early as 1989, Alcoa registered and declared the first RRA treatment process specification with the name of the heat treatment state of T77, which is also the first industrial application of the heat treatment process specification, this process specification can be used as the heat treatment process operation guidance for 7150 aluminum alloy. The 7150 aluminum alloy thick plate and extruded parts produced by this process are widely used in C-17 military transport aircraft. In China, the key technology of high-performance aluminum alloy using T77 heat treatment technology is still in the development process and has not been industrialized.
The heat treatment process also includes deformation heat treatment, deformation heat treatment is through the 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 alloy inside, reasonable deformation heat treatment can make aluminum alloy obtain higher strength and toughness and corrosion resistance. The deformation heat treatment process was proposed as early as 1981, which is mainly used in aerospace structural alloys. The deformation heat treatment has obvious effect on improving the mechanical properties of 7050 and 7475 alloys.
In China, there are only more than 100 kinds of aluminum alloy heat treatment process, and there is still a great distance from more than 370 kinds of foreign countries. We should increase the development of heat treatment process and shorten the distance of aluminum alloy basic heat treatment technology in developed countries.
03, high strength aluminum alloy 3D printing process
The development of low-cost, high-efficiency and automated high-strength aluminum alloy process technology has received the attention of aerospace, and large-scale aluminum alloy or titanium alloy 3D printing technology is the focus of current aerospace attention. 3D printing technology, as a prospective strategic technology in China, plays a vital role in the development of engineering applications.
In the aerospace field, although aluminum alloy has a large number of applications, but the actual application process compared to titanium alloy and composite materials there are certain drawbacks, such as aluminum alloy exposed to more than 160℃ in the application of mechanical properties and corrosion resistance, fatigue properties will decline, and with the extension of the use of time will soften and aging. Therefore, a lot of work needs to be done to improve the comprehensive performance of aluminum alloy in extreme working conditions.
Through the continuous maturity of 3D printing technology, the development of high-strength aluminum alloy powder is also continuing, and new aluminum alloy materials continue to emerge and continue to refresh new highs in performance. For example, Amaero HOT Al, a new type of aluminum alloy jointly developed by Amaero and Monash University in Australia, can achieve long-term stability at 260 ° C after 3D printing and then continue to undergo heat treatment and age hardening. The development of commercial high-strength aluminum alloy new materials to adapt to the 3D printing process to achieve the intelligent manufacturing performance of aluminum alloy controllable and highly complex shape has become the main trend of future development. Aluminum alloy 3D printing development prospects can be expected, mainly used in aerospace and military fields.
