Application of aluminum alloy in aircraft and aerospace vehicle
All aluminum materials (plates, foils, tubes, rods, shapes, wires, forgings, die castings, castings, etc.) are used in aerospace and spacecraft, but the most used are plates and profiles. At present, aluminum is still the leading material for civil aircraft, but with the development of technology, the proportion of aluminum in civil aircraft and other materials is slowly decreasing from generation to generation.
B777 passenger plane adopts high strength, high toughness and corrosion-resistant aluminum alloy. In the aircraft structure, it is traditionally used to use 2024 aluminum alloy in the parts prone to damage, and 7075 aluminum alloy in the places with high strength requirements. According to Boeing, since 1943, after 7075 and 2024 aluminum alloys, about 20% of new structural aluminum alloys have been widely used in Boeing aircraft. For example, compared with 7075 aluminum alloy, the composition of 7050 aluminum alloy changes greatly, increasing the content of Zr and Cu, while the impurities of Fe and Si are greatly reduced, so the strength, fracture toughness and stress corrosion resistance of this alloy are significantly better than that of 7075 aluminum alloy, especially its quenching sensitivity is low, so it is very suitable for manufacturing thick section forgings. 2324-t39 and 2224-t351 aluminum alloys are also improved on the basis of 2024 aluminum alloy, and their fracture toughness and stress corrosion resistance are significantly improved. From Boeing 737 to 767 aircraft, the most successful use experience of aluminum alloy is: 7150-t651x aluminum alloy is used for the upper wing surface, 2324-t39 and 2224-t351 1 aluminum alloy is best for the lower wing surface, and 7050 aluminum alloy should be considered for thick forgings. However, the process of obtaining this experience is very tortuous. Now, the above wing material selection is taken as an example. The upper wing structure is mainly under pressure, so the strength should be taken into account when selecting materials. For this reason, 7178 high-strength aluminum alloy is used in Boeing 707 and 737 aircraft. Due to the addition of Zn, Mg and Cu with higher content, the strength is improved, but the fracture toughness is reduced. At this time, for the consideration of damage tolerance, 7075-T651 aluminum alloy with lower strength but can ensure the fracture toughness is turned to be studied, It has been applied in Boeing 747 aircraft. Simultaneous 7 × × × The improvement of strength of 7075-t7651 aluminum alloy is accompanied by the decrease of corrosion resistance, especially in the peak aging state, which promotes the research of corrosion resistance t7651. 7075-t7651 aluminum alloy is used for the first time on Lockheed l101 aircraft. At the same time, 7079 aluminum alloy is used on Boeing 737 aircraft for fuselage wall panels, frames, landing gear beams, etc. the materials are T61 and t652 aging state to reduce heat treatment stress. However, 7079 aluminum alloy has poor stress corrosion resistance, so it is cancelled in the new Boeing aircraft material standard together with 7178 aluminum alloy.
In the Boeing 757 / 767 aircraft, new and stricter requirements are put forward for the alloy of the upper wing surface. This requirement is met by 7150-t651 aluminum alloy, which has the same strength as 7178-t651 aluminum alloy and has acceptable fracture toughness. Since then, in order to improve the stress corrosion resistance, a new heat treatment state t6151 has been developed. Under the premise of not reducing the strength, the corrosion resistance of 7150 Aluminum Alloy in this state has been slightly improved. It is used for the upper wing structure of Airbus A310 and McDonnell Douglas MD-11 aircraft. In view of the previous experience that strength, corrosion resistance and toughness can not be taken into account, people try to find a process that can not only maintain corrosion resistance but also not sacrifice strength. Based on this heat treatment state called T77, 7150-t7751 and 7150-t7751 1 aluminum alloy materials are produced. Their strength, toughness and corrosion resistance are well combined, and they are selected for McDonnell Douglas C-17 military transport aircraft. However, the strength of this alloy still can not meet the demand, so in recent years, a new 7055-t77 aluminum alloy material with higher strength and acceptable fracture toughness and corrosion resistance has been developed for the new civil aircraft Boeing 777. The nominal composition (mass fraction /%) of 7055 aluminum alloy is 8.1zn, 2.05mg, 2.34cu, < 0.15fe, < 0.1si, and the rest is al. Its performance is improved obviously. The specific compressive yield strength and specific tensile yield strength of 7055 aluminum alloy are about 10% higher than those of 7150-t6 and T77 aluminum alloy, and the strength is about 25% higher than that of 7075-T6 and 40% higher than that of 7075-t7. The corrosion resistance of 7055-t7751 and t7751 1 aluminum alloys is between 7150-t6 and 7150-t77 aluminum alloys. The plane stress fracture toughness value (KC) of 7055-t7751 aluminum alloy sheet is slightly lower than that of 7150-t6 / T77 aluminum alloy, but the plane strain fracture toughness value (K1C) of the two is almost the same.
It can be seen from the above that adjusting the alloy composition and improving the heat treatment state are the improvement ways of aluminum alloy at present. Since the fracture toughness of the fuselage material is critical × × × In addition to the modified aluminum alloy, Boeing also adopted 2 × × × - T3 aluminum alloy, called c-188, is characterized by good corrosion resistance. Its composition and production method are patented. It is known that compared with the candidate 2091-t3 and 8090-t81 Al Li alloys, the long transverse fracture toughness is 1 / 6 and 3 / 4 higher respectively. Under the same strength condition, the toughness and crack propagation resistance of 2024-T3 aluminum alloy are 20% higher than that of 2024-T3 aluminum alloy, and it has good corrosion resistance. Weldalite tmt8 aluminum lithium alloy was originally intended to be used for the upper wing surface of Boeing 777 aircraft. However, because the toughness of aluminum lithium alloy is not good, 7055-t7751 aluminum alloy was used, and its toughness was increased by 1 / 3. In contrast to the United States, Airbus uses aluminum lithium alloy for the secondary structure of A330 / A340 aircraft, and aluminum lithium alloy is also widely used in the CIS civil aircraft.
The application of aluminum in some foreign military aircraft, of which the F-22 aircraft uses the least aluminum, accounting for only 15% of the total amount of aluminum. The general trend is that with the upgrading of military aircraft, the consumption of aluminum materials is decreasing from generation to generation. Therefore, it is a severe challenge for the aluminum industry to develop a batch of new aluminum alloys with good comprehensive performance that can meet the needs of new military aircraft.
Aluminum is used in any rocket to spacecraft launch vehicle. From China's Long March No. 1 rocket to long march No. 4 rocket, the structures are mostly hard shell and semi hard shell structures composed of metal plates and reinforcements. The materials are mostly aluminum alloys with high specific strength and specific stiffness, and some stainless steel, titanium alloys and non-metallic materials are also used. However, aluminum alloys account for more than 70% of the total mass of structural materials. The structural materials of Long March No. 1 to No. 4 rockets are basically aluminum alloys. Except for a small part imported, the rest are provided by Northeast Light Alloy Co., Ltd. and Southwest Aluminum Industry (Group) Co., Ltd. Aluminum materials are mainly used for manufacturing fuel tanks and combustion supporting agent tanks in rockets and spacecraft. At the beginning of aerospace development, the United States adopted 2014 aluminum alloy. Later, due to the development and maturity of automatic welding technology, 2219 aluminum alloy was used. In terms of stress corrosion cracking performance, 2219 aluminum alloy is superior to 2014 aluminum alloy. The stress corrosion cracking stress of the latter in the short transverse direction is 53.9 n / mm2. The fuel tanks of Thor Delta and Saturn S-II rockets are made of 2219 aluminum alloy. In addition to the combustion aid tank, other structures of the rocket and space shuttle are the same as those of the aircraft. 2024 and 7075 aluminum alloys are mostly used, and 2219 aluminum alloys can also be used.
The aluminum material for spacecraft structure is basically the same as that for aircraft. Most of the main parts of the skeleton and control rod of manned aircraft are made of 7075-T73 high-strength aluminum alloy bar, which is thin and light and has high strength. Other parts such as bracket, pressing plate folding device, protective plate, door and skin plate, nitrogen cylinder of two thrusters are made of 6061-T6 aluminum alloy with good formability and medium strength.
