Aviation aluminum alloy is the backbone material of aircraft and space vehicle manufacturing. With the continuous improvement of flight performance, payload, fuel consumption, service life and safety and reliability requirements of modern aircraft design and manufacturing, more and more high requirements are put forward for the comprehensive performance and reduction effect of aluminum alloy structure. The whole aluminum alloy structure is processed by nc milling of large size aluminum alloy material, instead of the traditional composite structure composed of many aluminum alloy parts, which can not only reduce the weight of the structure, improve the reliability of service process, but also reduce the aircraft assembly process and reduce the manufacturing cost. This advanced design and manufacturing method, very stringent requirements for aluminum alloy material is put forward: the biggest thickness of aluminum alloy forgings or pre-stretching board often need to reach more than 150 mm, highly uniform for the comprehensive performance of different thickness of the parts, but also has excellent strength – plastic – fracture toughness – anti-fatigue performance – stress corrosion and spalling corrosion resistance matching.
Aluminum was used as the primary propellant for the space shuttle’s solid rocket booster engines because of its high volumetric energy density and difficulty in igniting accidentally.
Aluminium alloy plates are used in a wide range of aerospace applications, with complexity and performance requirements ranging from simple components to the main load-bearing structures of aircraft such as the Airbus A340 and Boeing 777.
The aircraft and aerospace industries have long relied on aluminum. Without the use of aluminium alloy in engines, the first aircraft would never have flown. Sputnik is made of aluminum, so it can survive its journey through our hot outer atmosphere and into space. Even today, NASA uses a mix of aluminium-lithium in advanced Orion spacecraft.
Aluminium is a crucial material for designing commercial aircraft and building sophisticated space shuttles. Aluminum alloys are most commonly used in the manufacture of fuselages, wings and support structures, providing a range of benefits for aircraft and space flight engineering.
Aerospace aluminium alloys are used to deal with sub-zero temperature conditions encountered in the freezing vacuum of space. On the other hand, aluminum alloys used in aircraft manufacturing have durability and the ability to resist various kinds of corrosion. The high stability of these alloys makes them ideal for use in mechanical parts that also benefit from aluminum’s high conductivity.
Aluminum alloy is mainly used as structural material in aircraft, such as skin, frame, propeller, fuel tank, siding and landing gear strut. The application and development of aluminum alloy in aerospace can be divided into several stages: in the 1950s, the main goal is to reduce weight and improve the specific stiffness and strength of the alloy; In the 1960s and 1970s, the main objective was to improve the durability and damage tolerance of alloys. The heat treatment systems of T73 and T76 of 7XXX series alloys, 7050 alloys and high purity alloys were developed. Further structural weight reduction was required in the 1980s due to rising fuel prices; Since the 1990s, the development goal of aluminum alloy is to further reduce weight, and further improve the durability and damage tolerance of the alloy. For example, a new type of aluminum alloy with high strength, toughness and corrosion resistance has been developed. A large number of complex integral structural parts are processed by thick plates instead of the parts assembled by many parts before, which can not only reduce the weight of the structure, but also ensure the stability of the performance. This can be achieved by developing thick plate materials with low internal stress.
Aluminum in aviation applications Aluminum is widely used in aircraft, mainly as aircraft structural parts. Aluminum alloy, due to its high specific strength, good shaping and machining performance, is the main structural material of aircraft, such as skin, frame, propeller, fuel tank, siding and landing gear prop. Different models of aluminum ratio can differ greatly, such as Boeing 737 aluminum alloy material accounted for a relatively large up to 81%, and Boeing 787 due to the use of a large number of composite materials, aluminum alloy material accounted for 20%. The aluminum used in aviation is mainly deformed aluminum, and the casting material is relatively low. In aircraft aluminum consumption, on average, flat rolled materials account for about 60%, extruded materials (tubes, rods, moulds and wires) for about 28%, forgings for about 7% and castings for about 5%.
According to the alloy composition, 2 series and 7 series are the main aluminum used in aviation. Aluminum alloys used in large aircraft structures in the world are mainly high strength 2 series (2024, 2224, 2324, 2424, 2524, etc.) and ultra high strength 7 series (7075, 7475, 7050, 7150, 7055, 7085, etc.), accounting for about 38% and 45% of the aluminum materials used in civil aircraft respectively. People have carried out in-depth systematic research on the composition and synthesis method of aerospace aluminum alloy, rolling/extrusion/forging/heat treatment and other processes, parts processing, material and structure service performance characterization and other aspects. The development of material products has formed a series of serialization, and a series of remarkable achievements have been made in the application. Especially since the end of 1980s, with the gradual formation of damage tolerance and durability design criteria for aircraft, higher requirements have been put forward for comprehensive properties such as strength, fracture toughness, corrosion resistance and fatigue resistance of materials. At present, the development direction of aluminum alloy is to develop thick plate materials with low internal stress, and a large number of thick plates are used in the manufacturing process to realize the forming of integral structural parts, instead of the parts assembled with many parts before (FIG. 2). The wide use of large integral panel structure has become an important means to improve the structural efficiency, reduce the number of parts, reduce the cost and shorten the development cycle of the new generation of aircraft. For example, the number of parts is reduced from 129 to 7, the cost is reduced by 25%, and the crack growth life and residual strength are increased by 3 times.
A generation of aircraft, a generation of materials, aviation aluminum has developed to the third generation of aluminum alloy represented by aluminum lithium alloy. The development of aviation aluminum has three stages: the first stage was 1930s-1960s, 2 series aluminum alloy made all-metal aircraft become the mainstream, and 7 series aluminum alloy represented by the early 7075 made aircraft in the stratosphere flight become possible, representative models are DC-3, B-29 and 70; In the second phase, 1960-1990s, a series of new 7-series aluminum alloys, such as 7050 and 7055, were developed, which improved specific strength while taking into account fatigue characteristics. Representative models are A300 series and 777. The third stage is from 2000 to now. Under the competition of composite materials, the third generation of aluminum alloy represented by aluminum lithium alloy is adopted by more and more new models, including A220, China’s C919, etc., and the representative brands are 2050 and 2196 of Kenya Union, and 2099 and 2397 of Alcoa. In addition to al – li alloy, al – matrix composites and superplastic forming aluminum alloy are also the key research directions of aviation aluminum.