Aluminum has become an extremely important key material in launch vehicles because of its low density and excellent low temperature performance. The liquid hydrogen liquid oxygen fuel tank is made of aluminum alloy, the main structural parts of the cabin section are also made of aluminum alloy. Now the carrier rocket structural material has entered the fourth generation, that is, containing a small amount of Li 2-series, 5-series alloy era, the main alloy for 2195,2196,2098,2198,2050. There is still a big gap between China and foreign countries in the development of Al-Li aluminum alloys in aerospace, but China can catch up with or surpass them to become the world leader around 2025. Due to its low density (≤2.8 G/cm3) , high specific strength and specific stiffness, corrosion resistance, fatigue resistance, good toughness, excellent processing and forming performance, it is an industrial metal with abundant resources, moderate price, harmless to human body and environment, and best cycling performance, therefore, it has been widely used in various sectors of the national economy and has become the second largest metal. In 2020, the world’s production of primary and secondary aluminum is about 95,000 kt, which is an indispensable material in all fields from daily necessities to aerospace. In today’s launch vehicle structural materials, aluminum, aluminum matrix composites is the largest amount of a class of materials. According to the author’s estimation, the net mass of aluminum and aluminum alloy is more than 85% of the total net mass of the structure and parts of the launch vehicle.

1. The material used in tank structure is closely related to rocket structure design, manufacturing technology, material preparation technology and economy, which is the key to determine the rocket take-off quality and payload capability. According to the development course of material system, the development course of rocket fuel tank material can be divided into four generations. The first generation is 5 series aluminum alloy, namely Al-Mg series alloy, which represents 5A06 and 5A03 alloy. 5A06 alloy contains 5.8% ー6.8% Mg since it was used to manufacture P-2 rocket fuel tank structure at the end of 1950s, 5A03 is an Al-Mg-Mn-Si alloy. The second generation is Al-Cu series 2 alloy. The Chinese Long March tank is made of 2A14 alloy, which is an Al-Cu-mg-mn-si alloy. From the 1970s to the present, China has started to make tanks with 2219 alloy, this is an Al-Cu-Mn-V-Zr-Ti alloy, which is widely used in the manufacture of all kinds of launch vehicle tanks, and also widely used in the structure of weapon launch cryogenic fuel tanks The third generation is Al-Li alloy, that is, 2-series alloy containing less than 3.0% Li and 5-series alloy, the former is adopted by USA, UK, Germany and Japan, while the latter is developed by Russia and has been used abroad since the 1980s, it has already entered the stage of industrialized preparation and engineering application, but at present China has only a small scale application in aviation industry.

2. On November 3,2016, China successfully launched the Long March 5 carrier rocket, nicknamed “Fat five”. The diameter of the rocket is 50% larger than that of the rocket in service in China, the diameter of the core stage is 5m, and the diameter of the booster is 3.35 m, while the diameter of the core stage and the booster are 3.35 m and 2.25 M. In addition to its “Waistline”, it is about 57m tall, the equivalent of a 20-storey building, second only to the long march-2f carrier rocket, which can hold more propellant (fuel) . The core stage 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 internal temperature of the Long March 5 is far below the freezing point of the ultra-low temperature, so it is also called “Ice Arrow.”. In the 800-ton body of the Long March V, 90% is liquid hydrogen and liquid oxygen. After ignition, the flame temperature of the engine is as high as 3000 °C, and the extreme state of “Ice and fire”is a great test of China’s space technology and materials used. The development of the Long March 5 took 10 years, which shows how difficult it is. In the course of development, 247 key technologies have been broken through, of which 12 are the most important, the proportion of new technologies is almost 100% , and the core technologies are all self-created, the Long March rocket has been upgraded by leaps and bounds. The LM-5 rocket has 12“Big hearts”, or engines, providing a total thrust of 10,564.4 kn. Eight liquid oxygen and kerosene engines are divided into four groups to form the auxiliary power, with a total take-off power of 9408 kn; two 490 kn hydrogen and Oxygen Engines to form the core first-order power and take-off power of 980 kn; two 88.2 kn expansion cycle hydrogen and oxygen engines to form the core second-order power. The low-orbit and high-orbit carrying capacities of the long march-5 launch vehicles can reach 25 t class and 14 t class respectively, crossing the “Threshold”of 20 T low-earth orbit carrying capacity and 10 T high-orbit carrying capacity of the international large-scale launch vehicles, it can run side-by-side with the world’s main large rockets such as U. S. Atlas 5, Delta 4 and European Ariane 5. Although China’s launch vehicle industry has made remarkable achievements, there are still some gaps compared with the world space power. The key technology foundation such as rocket engine and large diameter rocket body structure needs to be consolidated constantly, and the new model of research and development to reduce cost and improve competitiveness needs to be established and strengthened.

3. The first flight of the Long March 8“Five-star with one Arrow”was a success. At 1237 hours on December 22,2020, the first flight test of the new-type Comparison of orbital launch systems, the Long March 8, was a success. The Long March 8 carrier rocket fully inherits the achievements of the Long March 5 and Long March 7 technology, and fills the gap of the sun-synchronous orbit’s 3T ~ 4.5 t carrying capacity, it is of great significance to accelerate the upgrade of the propulsion launch vehicle. With a length of about 50m and a modular assembly concept, the launch cycle of the Long March 88 rockets will be shortened to 10d in the future, while vertical take off and landing technology will be used so that they can be launched more than once, it is estimated that this kind of space station can be completed around 2025. China plans to build a multi-module, inhabited space station around 2022. The total number of flights per year will reach the order of 1,000, the total cargo transport will reach the class of 10,000 tons, and the total number of passengers will reach 10,000 by 2045.

4. Development of structural materials for launch vehicle tanks and compartments and aluminum-lithium Alloy 01. The storage tank aluminum alloy carrier rocket has entered the third generation since the middle of 1980s, that is, the aluminum-lithium alloy era. Since the turn of the century, 2 series Al-Li alloys containing small amounts of lithium have been widely used, while in Russia, Al-Mg alloys containing small amounts of lithium have been used, and according to data from China Academy of Launch Vehicle Technology, even though China currently has only aviation applications, there are no examples of tank structures being used. Al-mg and al-cu alloys with a small amount of Li have a greater weight loss effect, compared with alloys without Li, the weight loss effect can reach 10% ~ 30% . Fortunately, some enterprises and research institutions in China, such as Southwest Aluminum (Group) Co. , Ltd. and Zhengzhou Light Metals Research Institute, have broken through the precise control of alloy composition through years of continuous hard work, some key technical bottlenecks, such as large size ingot casting and homogenization treatment, whole process fine microstructure control, large size plate deformation and heat treatment, have been realized, strength, toughness, low temperature properties and weldability have been improved in coordination, which has reached the goal of industrialized preparation. However, there are still some gaps in the stability and consistency of product properties, production cost, etc. when compared with the products of advanced countries abroad, 2025 is expected to be able to fully catch up with or exceed the foreign high-end products of the indicators. The heavy-lift launch vehicle has selected 2014,2219,2195,2198 and other aluminum alloys, while the United States in the selection of high-performance Al-Li alloy from the one-sided pursuit of the best performance has turned to a comprehensive consideration of cost factors. At present, the United States is actively developing a new generation of Al-Li alloy with better performance and lower cost, represented by 2050 alloy.

02. Aluminum Alloy for cabin structure from the development of launch vehicle in China in the 1960s until now, the aluminum alloy for cabin structure of launch vehicle is mainly the first and second generation alloys represented by 2A12 and 7A09, the fourth generation aluminum alloys 7055 and 7085, which have high strength, low quenching sensitivity and notch sensitivity, have been widely used abroad. 7055 is an Al-Zn-Mg-Cu-Zr alloy and 7085 is also an Al-Zn-Mg-Cu-Zr alloy, but its impurity Fe and SI contents are very low, and the Zn contents are high, ranging from 7.0% to 8.0% . The third generation Al-Li alloys, represented by 2A97 and 1460, have been used in the foreign space industry for their high strength, high modulus and high elongation. Grain reinforced aluminum matrix composites have the advantages of high modulus and strength, which can be used to replace 7A09 alloy to make semi-hard Shell section truss. The Institute of Metals, Harbin Institute of Technology and Shanghai Jiao Tong University have done a lot of work in the research and preparation of particle reinforced aluminum matrix composites. 03. The most successful applications of the Al-Li alloy abroad are the Weldalite Al-Li alloy family, which has been developed for eight years by Kenglian Aluminum Co. . ISSOIRE ROLLING MILL AND QUEBEC R & D Center, including 2195,2196,2098,2198,2050 alloys: 2195 alloy al-4.0 cu-1.0 li-0.4 mg-0.4 ag-0.1 Zr, which is the first Al-Li alloy to be successfully commercialized for the manufacture of low temperature fuel tanks for rocket launching; 2196 alloy al-2.8 cu-1.6 li-0.4 mg-0.4 ag-0.1 zr, low density, high strength, high fracture toughness, was originally developed for the frame profile of Hubble solar panel, and is now mostly used for extrusion of aircraft profiles; Alloy 2098: Al-3.5 cu-1.1 li-0.4 mg-0.4 ag-0.1 zr, originally developed for the manufacture of HSCT airframes, is now used as the launch fuel tank of the F16 fighter airframes and the Falcon spacecraft due to its high fatigue strength; 2198 alloy al-3.2 cu-0.9 li-0.4 mg-0.4 ag-0.1 Zr for Rolling Commercial Aircraft Sheet; 2050 Alloy al-3.5 cu-1.0 li-0.4 mg-0.4 ag-0.4 MN-0.1 Zr for producing heavy plate to replace 7050-T7451 alloy plate, cONSTRUCTION/LAUNCH rocket components for commercial aircraft. Compared with 2195 alloy, the content of CU + MN in 2050 alloy is lower in order to decrease quenching sensitivity and maintain high mechanical properties of thick plate, 4% higher specific strength and 9% higher specific modulus, and the fracture toughness is increased, there are high stress corrosion cracking resistance and high fatigue crack propagation resistance, in addition to high temperature stability. 

Source: Non-ferrous metal