Aluminum has become an extremely important key material in launch vehicles, because aluminum alloy has low density and excellent unparalleled low temperature performance. The liquid hydrogen and liquid oxygen fuel tank of the launch rocket is made of aluminum alloy. The main structure of the cabin The material used for the pieces is also aluminum alloy. Now the structural materials of the launch vehicle have entered the fourth generation, that is, the age of 2-series and 5-series alloys containing a small amount of Li. The main alloys are 2195, 2196, 2098, 2198, and 2050. China still has a big gap in the development of aerospace Al-Li aluminum alloy compared with foreign countries, but it can catch up or surpass them all around 2025 and become the world leader.
Because aluminum alloy has low density (≤2.8g/cm3), high specific strength and specific rigidity, corrosion resistance, fatigue resistance, good toughness, excellent processing and forming performance, rich resources, moderate price, harmless to human body and environment, recycling The industrial metal with the best performance has been widely used in various sectors of the national economy and has become the second largest metal. In 2020, the world’s primary aluminum and secondary aluminum production will be about 95,000 kt, which is a category that cannot be used in various fields from daily necessities to aerospace. Optional materials. Among the structural materials of today’s launch vehicles, aluminum and aluminum-based composite materials are the most used materials. According to the author’s estimation, in the structure and parts of the launch vehicle, the net mass of aluminum and aluminum alloy accounts for more than 85% of the total net mass of the structure.
Structural materials are closely related to a series of issues such as the design of the rocket body structure, manufacturing and processing technology, material preparation technology, and economy. They are the key to determining the rocket’s take-off quality and payload capacity. According to the development history of the material system, the development history of rocket fuel tank materials can be divided into four generations. The first generation is 5 series aluminum alloy, namely Al-Mg series alloy. The representative alloys are 5A06 and 5A03 alloys. They were used in the manufacture of P-2 rocket fuel tank structures in the late 1950s and are still used today. 5A06 alloy Containing 5.8% Mg～6.8% Mg, 5A03 is an Al-Mg-Mn-Si alloy. The second generation is the Al-Cu series 2 series alloy. The China Long March series launch vehicle tank is made of 2A14 alloy, which is an Al-Cu-Mg-Mn-Si alloy; from the 1970s to the present, China has begun to use it. 2219 alloy manufacturing tank, which is an Al-Cu-Mn-V-Zr-Ti alloy, is widely used in the manufacture of various launch vehicle tanks. At the same time, it is also widely used in the structure of weapon launch low-temperature fuel tanks. Alloys with excellent low-temperature performance and comprehensive performance; the third generation is Al-Li alloy, that is, the 2 series alloy and the 5 series alloy with Li content ≤3.0%. The former is used in the United States, Britain, Germany, Japan, etc., and the latter is It was developed by Russia and used abroad in the 1980s. It has already entered the stage of industrial preparation and engineering application. At present, China only has small-scale applications in the aviation industry, and the launch vehicle tank structure has not yet seen application examples.
Long March 5 Carrier Rocket
On November 3, 2016, China successfully launched the Long March 5 carrier rocket, nicknamed “Fat Five”. Its diameter is 50% larger than that of China’s active rockets, with a core stage diameter of 5m and a booster diameter of 3.35m, while China’s active rocket core stage has a diameter of 3.35m and a booster diameter of 2.25m. In addition to the large “waist circumference”, its “height” is about 57m, which is equivalent to a 20-story building, second only to the Long March 2 F carrier rocket, so it can accommodate more propellant (fuel). The core-level engine uses liquid hydrogen (-253°C) and liquid oxygen (-183°C), and the booster fuel is a combination of liquid oxygen and kerosene. In other words, the temperature inside the Long March 5 is much lower than the freezing point of ultra-low temperature, so it is also called “ice arrow.” In the body of the Long March 5 weighing more than 800 tons, 90% is liquid hydrogen and liquid oxygen. After ignition, the temperature of the flames emitted by the engine is as high as 3000℃. At this time, its extreme state of “ice and fire” inside and outside is a great test of China’s space technology and materials used.
The development of Long March 5 lasted for 10 years, which shows that it is very difficult. During the development, 247 key technologies have been broken through, of which 12 are the most important key technologies, and the proportion of new technologies is almost 100%. The core technologies are all self-created. , Has realized the leap-forward upgrade of the Long March rocket. The Long March 5 rocket has 12 “big hearts” or engines, providing a total thrust of 1,0564.4kN. 8 liquid oxygen kerosene engines are composed of 4 groups, which form the propelling force, with a total take-off power of 9408kN; 2 490kN hydrogen-oxygen engines are responsible for the core first-level power, and the take-off power is 980kN; two 88.2kN expansion cycle hydrogen-oxygen engines form the core second-level power. The Long March 5 series of carrier rockets can have a low-orbit carrying capacity of up to 25t and a high-orbit carrying capacity of up to 14t. They have crossed the international “threshold” of large-scale carrier rockets with a low-Earth orbit carrying capacity of 20t and a high orbit carrying capacity of 10t. Run side by side with the world’s major large rockets such as the American Space God 5, Delta 4, and the European Ariane 5.
Although China’s launch vehicle industry has achieved world-renowned achievements, there are still some gaps in comparison with the world’s aerospace powers. The type spectrum of launch vehicles needs to be continuously improved, and the key technology foundations such as rocket engines and large-diameter rocket body structures need to be continuously consolidated. New development models for reducing costs and increasing competitiveness need to be established and strengthened.
Structural materials of carrier rocket tanks and compartments The development of aluminum-lithium alloys
Aluminum alloy storage box
The structural materials of launch vehicle tanks abroad have entered the third generation, the age of aluminum-lithium alloys, since the mid-1980s. Since the beginning of the new century, 2-series Al-Li alloys containing a small amount of lithium have been adopted on a large scale, while Russia has adopted Al-Mg alloys containing a small amount of lithium. It has been applied in the aviation field, and there is no application example of the storage tank structure. Aluminum-magnesium and aluminum-copper alloys containing a small amount of Li have a greater weight reduction effect. Compared with alloys without Li, the weight reduction effect can reach 10% to 30%.
Fortunately, some Chinese enterprises and research units such as Southwest Aluminum (Group) Co., Ltd. and Zhengzhou Light Metal Research Institute have broken through the precise control of alloy composition, large-scale ingot casting and homogenization through years of continuous hard work. , The key technical bottlenecks such as the fine control of the whole process of microstructure, large-size sheet deformation heat treatment, etc., realized the homogenization of large-size Al-Li alloy, and the synergistic improvement of strength, toughness, low temperature performance, weldability, etc., and reached the goal of industrial preparation However, compared with the products of advanced foreign countries, there are still some gaps in product performance stability and consistency, production costs, etc. It is expected that it will not be able to fully catch up or exceed the various indicators of foreign high-end products by 2025.
The American heavy-duty launch vehicle tank has successively selected aluminum alloys such as 2014, 2219, 2195, and 2198. At the same time, the United States has shifted from one-sided pursuit of the best performance to comprehensive consideration of cost factors in the process of selecting high-performance Al-Li alloys. At present, the United States is actively developing a new generation of Al-Li alloys represented by 2050 alloys with better performance and lower cost.
Cabin structure aluminum alloy
Since the development of carrier rockets in China in the 1960s until now, the aluminum alloys of the carrier rocket cabin structure are mainly the first and second generation alloys represented by 2A12 and 7A09, while foreign countries have entered the fourth-generation cabin structure aluminum Alloy 7055, 7085 alloy, they have high strength properties, low quenching sensitivity and notch sensitivity and are widely used. 7055 is an Al-Zn-Mg-Cu-Zr alloy, 7085 is also an Al-Zn-Mg-Cu-Zr alloy, but its impurity Fe and Si content is very low, while the Zn content is high, 7.0% ~8.0%. The third-generation Al-Li alloys represented by 2A97, 1460, etc., have been used in the foreign aerospace industry with their high strength, high modulus, and high elongation.
Particle-reinforced aluminum-based composite material has the advantages of high modulus and high strength, and can be used to replace 7A09 alloy to make semi-monocoque cabin stringers. The Institute of Metal Research of the Chinese Academy of Sciences, Harbin Institute of Technology, Shanghai Jiaotong University, etc. have done a lot of work in the research and preparation of particle-reinforced aluminum matrix composites, with remarkable achievements.
Foreign Aerospace Al-Li Alloy
The most successful application in foreign aerospace vehicles is the Weldalite Al-Li alloy family developed by Kenlian Aluminum Company Issoire Rolling Mill and Quebec R&D Center for 8 years, including 2195, 2196, 2098, 2198, 2050 Alloy: 2195 alloy: Al-4.0Cu-1.0Li-0.4Mg-0.4Ag-0.1Zr, which is the first Al-Li alloy successfully commercialized to be used in the manufacture of low-temperature fuel tanks for rocket launches; 2196 alloy: Al-2.8Cu-1.6Li-0.4Mg-0.4Ag-0.1Zr, low density, high strength, high fracture toughness, originally developed for Hubble solar panel frame profiles, now it is mostly used to extrude aircraft profiles; 2098 alloy: Al-3.5 Cu-1.1Li-0.4Mg-0.4Ag-0.1Zr, originally developed for the manufacture of HSCT fuselage, because of its high fatigue strength, it is now used in F16 fighter fuselage and spacecraft Falcon ( Falcon) launch fuel tank; 2198 alloy: Al-3.2Cu-0.9Li-0.4Mg-0.4Ag-0.1Zr, used for rolling commercial aircraft sheet; 2050 alloy: Al-3.5Cu-1.0Li-0.4Mg- 0.4Ag-0.4Mn-0.1Zr, used to produce thick plates to replace 7050-T7451 alloy thick plates, used to manufacture commercial aircraft structures/launch rocket components. Compared with 2195 alloy, the Cu+Mn content of 2050 alloy is relatively low to reduce the quenching sensitivity and maintain the high mechanical properties of the thick plate. The specific strength is 4% higher, the specific modulus is 9% higher, and the fracture toughness is increased. Stress corrosion cracking resistance and high fatigue crack growth resistance, in addition to high temperature stability.
Post time: Jun-04-2021