[CHINA ALUMINUM NETWORK] China's new generation medium-sized launch vehicle, the Long March 7, was successfully completed on June 25 at the newly-built Wenchang Space Launch Site in Hainan Province, marking the successful start of the mission of China's manned space project. The Long March 7 rocket has a total length of 53.1m, a take-off mass of 597t and a low-Earth orbit carrying capacity of 13.5t. It has 4 boosters, a diameter of 2.25m and a length of 27m. It uses liquid oxygen-kerosene as fuel, which is non-toxic and pollution-free. When kerosene and oxygen are combusted, they all become carbon dioxide and moisture, and they have no other substance. The diameter of the core is 3.35m. The Long March 7 rocket is light in weight, its structure and equipment quality only account for 10% of the total mass, so it can hold more fuel and transport more “passengersâ€.
The entire rocket consists of a fairing, instrumentation chamber, secondary liquid oxygen tank, secondary fuel tank, booster cone head, booster liquid oxygen tank, first-order liquid oxygen tank, first-grade coal tank, booster fuel tank, first-order tail Segments, and push tail segments.
The aluminum alloy played a decisive role in the success of the Long March rocket. Without aluminum, the rocket’s ascension to the sky is difficult to achieve so far. Liquid oxygen, liquid hydrogen, and kerosene are combustion aids and fuels for rocket engines. Oxygen becomes liquid at 1 atmosphere and -182.97°C, and hydrogen becomes liquid at 1 atmosphere and -252.8°C. Therefore, the containers for storing liquid oxygen and liquid hydrogen must have good low-temperature performance. We know that ordinary structural steels and other non-ferrous metals other than aluminum have low-temperature brittleness, that is, their plasticity and toughness both decrease with temperature. Significantly decreased, but aluminum alloy is a very good low-temperature alloy, and its mechanical properties and processing and forming properties rise correspondingly with the decrease of temperature. Therefore, aluminum alloy is the preferred material for the production of liquid hydrogen, liquid oxygen storage and transportation containers, it has better overall performance: the density is small, this performance is very important and outstanding for the aerospace vehicle; no low temperature brittleness; processing Good formability, high mechanical properties, good recyclability, excellent weldability, and particularly easy friction stir welding.
What material was used for the oxygen box and the fuel tank of the Long March 7 rocket?
To be sure, it is made of aluminum alloy. As to what kind of aluminum alloy is used, it is very likely that it is 2219 alloy because it has a good overall performance. At the same time, the liquid hydrogen and liquid oxygen boxes of foreign launch rockets are welded with it. The total mass of the Saturn-Apollo launch vehicle launched by the United States is about 3,000 tons, and the mass of liquid oxygen exceeds 2000 tons. The storage tanks are all welded with 2219 alloy.
2219 aluminum alloy: treasure of aerospace materials
2219 aluminum alloy is an Al-Cu-Mn-Ti-V-Zr alloy, which has now formed a large family of 4 brothers: 2219, 2319, 2419, 2519, 2219 alloy was born in the early 1950s, 2519 alloy Registered in 1985, but 229 alloy after nearly 70 years of use and testing is not old, is still a major aerospace aluminum alloy, rocket fired low temperature fuel tank is welded with its plate, the United States with friction stir welding (FSW) automatic Welding, their chemical composition is shown in Table 1.
The 2219 aluminum alloy was developed for the development of the aerospace industry and is a major breakthrough in the research of conventional aerospace aluminum alloys after the 7075 alloy. From the composition listed in Table 1, it can be seen that the main alloying element is only Cu, whose content is much higher than that of the 2024 alloy, which is about 45% higher. The second feature is that there are many minor alloying elements, including Mn and Ti. V, Zr, which are all high-melting elements, can form infusible binary compounds with Al, such as Al6Mn, Al3Ti, Al3Zr, Al3V, etc. These elements have refined the ingot casting grain and improve the recrystallization of the alloy. Temperature; Third, the impurity Fe, Si content is low, in addition to 2519 alloy containing 0.05% ~ 0.40% Mg, magnesium is also an impurity in the other three alloys, Zn is also considered an impurity, due to low Fe, Si content, so The formation of insoluble impurities is rare, Mg and Zn are all dissolved in Al, so these impurities have little or no effect on the properties of the alloy. We can think of the 2219 alloy as a binary Al-Cu alloy. Of course, due to the large number of minor alloying elements, it can also be regarded as a complex multi-element alloy.
Alloy properties
First of all, the 2219 alloy is an alloy with a wide range of service temperatures. It can be used in extremely low temperature environments as low as -269°C. It is a low-temperature alloy, and its mechanical properties rise synchronously and evenly as the temperature decreases. It can also work in a high temperature environment up to 300°C (Table 2). Therefore, it is an alloy with an operating temperature range up to 569°C, which is wider than any other existing aluminum alloy and is a low-temperature alloy. It is also a kind of high-temperature alloy. It is a kind of cow's aerospace alloy.
Good solderability. High weld strength can be obtained with 2319 alloy electrode or welding wire. After friction stir welding, the tensile strength of the weld and heat affected zone is almost equal to that of the matrix material. Spacecraft rocket liquid oxygen, liquid hydrogen are welded by this method, without electrodes or welding wire.
2219 alloy has a low impurity content and is a fairly clean alloy, so its fracture toughness is high, especially in the short transverse (thickness direction), T8 state alloy has a high resistance to stress corrosion cracking, extremely valuable, tensile elastic modulus E = 73.8 GN/m2, compressive modulus of elasticity 75.2 GN/m2, and Poisson's ratio of 0.33. RR molar test fatigue strength (cycle number 5 x 108) 103 N/mm2.
2219 alloy thermal properties: liquidus temperature of 643 °C, low melting point eutectic starting melting temperature of 543 °C, linear expansion coefficient is as follows:
Temperature range, °C Average linear expansion coefficient, μm/(m·k)
-50~+20 20.8
20~100 22.5
20~200 23.4
20~300 22.4
Body expansion coefficient 6.5×10-5m3/(m3·k); Specific heat capacity at 20°C 864J/(kg·K); Thermal conductivity, 170W/(m·k) in the O-state, 116W/T31 and T37 states (m·k), 130W/(m·k) for T62, T81, and T87 states; volume conductivity at 20°C: 44% IACS for O state, 28% IACS for T31, T37, and T351 states, T62, T81 The T87, T87, and T851 states are 30% IACS.
The resistivity of the 2219 alloy at 20°C: 39nΩ·m in the O state, 62nΩ·m in the T31, T37, and T351 states, and 57nΩ·m in the T62, T81, T87, and T851 states. The temperature coefficient of resistance of each state material is 0.1nΩ·m/K (20°C).
Potential of Alloy 2219: Potential of 0.1 calomel electrode in an aqueous solution containing 53 g of NaCl and 3 g of H2O3 at 25°C, -0.64 V of T31, T37, and T351 state materials, -80 V of T62, T81, T87, and T851 state materials .
2219 alloy annealing temperature 535 °C, artificial aging specification: 165 °C ~ 190 °C, 18h ~ 36h, the specific artificial aging temperature and holding time depends on the desired state. 2219 alloy has no natural aging ability.
2219 alloy semi-finished products are plate, belt, tube, rod, type, wire and forgings, plate, strip with aluminum, but also does not pack, wire for processing rivets, electrodes, welding wire. The material states are: O, T42, T31, T351, T37, T62, T81, T851, T87.
The 2219 alloy is mainly used in the aerospace field. Enterprises producing such alloys must possess modern equipment and technologies for producing such materials. The United States has an advantage in producing such alloys.
China's Longer Five-Year Rocket Will Also Be Launched
China’s larger rocket, the Long March 5 launch vehicle, developed by China Aerospace Science and Technology Corporation will complete its first flight in the second half of the year. According to media reports, it is China’s current high-height, bulky, and highly capable rocket. The outstanding features of “Chang 5†are the new technology and complex design, the application of 247 advanced core technologies and the integration of a number of newer aerospace technologies. The adoption rate of new parts and components technology has reached almost 100%, and China has fully independent intellectual property rights. . What is amazing is that the total mass of “Chang 5†is more than 800 tons, of which the liquid hydrogen at −252° C. and the liquid oxygen content at −183° C. account for about 90%, ie about 720 tons is liquid oxygen/kerosene, liquid hydrogen/liquid. Oxygen and low-temperature propellant combination, completely non-toxic, pollution-free and environmentally friendly fuel, but the liquid hydrogen temperature is as low as -252°C, which poses greater challenges to structural design of power plants. Liquid hydrogen, liquid oxygen and other fuel containers are undoubtedly welded with 2219 aluminum alloy plates that are not afraid of freezing. The Long March V rocket is the single carrier rocket that has used aluminum alloys in China so far.
The specific time for the first flight of the "Chang 5" has not yet been finalized, but its number of parts and components is as high as 140,000. Its manufacturing and launching will not only greatly enhance and further consolidate the position of the Chinese carrier rocket in the world's space industry, but also Accelerate China's transformation from aerospace to power. "Chang 5" is mainly used for launching Cangwu No. 5, the space station's core module and the Mars rover. They are all major national special space projects.
It is said that after the first flight, the "Chang 5" will continue to be developed and serially produced. This will also promote the development of the domestic space science and space applications industry more effectively, promote scientific and technological progress in various fields, and promote economic growth. Ten thousand enterprises will lead to the transformation and upgrading of the national economy and the strengthening of national defense construction. The aluminum industry will be one of the major beneficiaries. (Wang Zhutang)
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