Aluminum alloys are mainly used as structural materials in aircraft, such as skins, frames, propellers, fuel tanks, wall panels and landing gear struts. The application and development of aluminum alloys in aerospace can be divided into several stages: in the 1950s, the main goal was to reduce weight and improve the specific stiffness and strength of the alloy; in the 1960s and 1970s, the main goal was to improve the durability and damage tolerance of the alloy. 7XXX series alloys T73 and T76 heat treatment systems, 7050 alloys and high-purity alloys; in the 1980s, due to rising fuel prices, further structural weight reduction was required; since the 1990s, the development goal of aluminum alloys is to further reduce weight and further improve the durability of the alloy and damage tolerance. For example, a new type of aluminum alloy with high strength, high toughness and high corrosion resistance has been developed, and a large number of thick plates are used to process complex integral structural components instead of components previously assembled with many parts, which can not only reduce the structural weight, but also ensure stable performance. Achieving this requires the development of thick plate materials with low internal stress.
Aluminum alloy thick plate is an important structural material in the modern aerospace industry. At present, the aluminum industry in developed countries has continuously developed new aluminum alloy thick plates with excellent performance. Among them, there are the following common alloys, one of which is 7075-T7651 aluminum alloy thick plate. , it has high strength, good toughness, stress resistance and anti-stripping corrosion resistance, it belongs to aluminum-zinc-magnesium-copper superhard aluminum alloy, which is widely used in aircraft frames, integral wall panels, landing gear, Leather etc. The second is 7055 super-hard aluminum alloy, which is the alloy with the highest strength among the deformed aluminum alloys. The strength of the 7075-T77 alloy sheet produced by Alcoa is 10% higher than that of 7150 and 30% higher than that of 7075, and it is fractured. Good toughness and strong resistance to fatigue crack growth. Aluminum alloy thick plate has good comprehensive performance as a material for aerospace, but there is also residual stress in quenching. The existence of residual stress seriously affects the subsequent processing and application of the material, especially when it is used as a structural part or Residual stress is a major cause of premature material failure and even serious accidents when working in corrosive environments. Therefore, it is very important to study the method of eliminating residual stress.
2000 series aluminum alloys have excellent temperature resistance and are mainly used in aerospace high temperature resistant parts. Strength stability and process performance are mostly used for heat-resistant parts and heat-resistant weldable structural parts and forgings that work in the temperature range of 150 to 250 °C. Impurities of iron (Fe) and silicon (Si) exist in 2000 series alloys. The presence of these two impurities will produce coarse impurity phases, which seriously affect the fracture toughness and short transverse mechanical properties. Therefore, from the consideration of adjusting the content of alloying elements and reducing the impurity phase of Fe and Si, the researchers improved the strength and toughness of 2000 series aluminum alloys and improved the heat resistance of aluminum alloys by adding nickel (Ni) elements. content to improve the welding performance of aluminum alloy materials. For thin-walled aluminum alloy materials, the damage tolerance performance is mainly improved, and for thick-walled aluminum alloy materials, its stress corrosion resistance performance and toughness are mainly improved. The best matching material.
7000 series aluminum alloys use Zn as the main additive element. The toughness of the aluminum alloy can be strengthened by heat treatment. After adding Mg element to the alloy, its hot deformation performance can be improved and the quenching range can be expanded. Changing the heat treatment conditions can improve the strength, weldability and corrosion resistance. However, the introduction of Mg element makes aluminum alloys have a serious tendency to stress corrosion. Therefore, 7000 series aluminum alloys belong to high-strength weldable alloys with high stress corrosion sensitivity. The Al/Zn/Mg/Cu alloy added with Cu element has higher strength and belongs to ultra-high-strength aluminum alloy. The yield strength is very close to the tensile strength. And the strength at high temperature is low, and it is often used for load-bearing structural parts where the operating temperature is lower than 120 °C. The excellent machinability, corrosion resistance and high toughness of 7000 series aluminum alloys make it the main structural material for aerospace. Internationally, it was recognized as early as the 1820s that the joint heat treatment after adding Mg and Zn to aluminum alloys has a strengthening effect, but there is a serious problem of stress corrosion cracking. Molybdenum (Mo) improves the problem of stress corrosion cracking and realizes a large number of applications on carrier-based fighter jets. Especially in 1943, the 7075 alloy developed by the United States was applied to the B-29 bomber for the first time, which brought revolutionary changes to the structure and performance of the aircraft. Subsequently, the 7000 series aluminum alloys were imitated and developed by various countries, and were widely used in high-end manufactured products. In the 1960s, the United States improved on the basis of 7075 aluminum alloy and developed 7050 alloy which is stronger, tougher and more resistant to stress corrosion. Alloy, used in the manufacture of the upper wing structure of large civil aircraft such as Boeing 757/767 and Airbus A301. In the 1980s, the United States successfully developed 7055 alloy on the basis of 7150. Its strength is about 10% higher than that of 7150, and it has high comprehensive performance. It is used for the upper wing skin and wing stringer of Boeing 777 passenger aircraft.