Big Aircraft: The ever-changing aerospace metal materials

In today's increasingly developed air transport, people are already familiar with the flight: with the powerful roar of the engine, the aircraft vacated, the landing gear slowly moved into the cabin, and the aircraft quickly disappeared on the horizon after a short climb. All of this relies on efficient body structures, powerful engines, strong landing gear, advanced systems, etc., and the main components of these components are aerospace metal materials.

One of the alloy families: aluminum alloy
In 1903, the United States Wright brothers invented the world's first aircraft, the choice of materials are wood and canvas, flying at only 16 kilometers per hour, and the speed of cycling is almost the same.
In 1911, aluminum alloys were successfully developed and quickly replaced wood and canvas, making them the main materials for manufacturing aircraft. During the First World War, all-metal aircraft were already common.
From the transition of the wooden structure to the metal structure, the speed and other properties of the aircraft achieved a leap. For example, by 1939, propeller aircraft had created a top speed of 755 kilometers, and in only 36 years, the flight speed of the aircraft increased by 47 times. Today, aluminum alloys still play an important role in the metal materials used in aircraft.
Aeronautical aluminum alloys have low density, good corrosion resistance, high specific strength, specific stiffness, easy processing and sufficient experience, which make them ideal materials for aircraft structures.
Since its inception, aluminum alloys have evolved with the requirements of aircraft design, and their performance has become increasingly powerful. For example, in 1954, three British "Iridium" aircraft crashed. Accident analysis showed that the main cause of the crash was material fatigue and severe corrosion of some 7075-T6 aluminum alloy components. After exploration, the researchers broke through the problem of over-aging heat treatment and developed the second-generation corrosion-resistant aluminum alloy, which effectively improved the safety level of the aircraft.
Today, the development of aviation aluminum alloy has entered the sixth stage. On April 27, 2005, the world's largest wide-body passenger aircraft, the Airbus A380, made its first flight at Toulouse Airport. The A380 is a success, and the application of advanced materials has made a great contribution. Among them, Alcan and Alcoa have developed new aluminum alloy materials for the A380.
As early as 1998, Alcan had an agreement with Airbus to form an integrated project team for the A380 aircraft to develop new aluminum alloy materials. According to the characteristics of the A380 components, Alcan has developed a series of aluminum alloys such as 7040-T7651, 7449, 2027-T3511. Each alloy has different properties and characteristics.
Taking the 7040-T7651 alloy as an example, the front beam and the central spar of the A380 outer wing place high demands on the static strength and fracture toughness of the material. At the same time, the material must also have good ductility and machinability. In order to achieve the above objectives, Alcan has improved the original alloy AA7010/7050-T7651 and developed a new alloy 7040-T7651. This alloy has high static strength, high toughness, low residual stress and good ductility.
Alcoa was founded in 1888. For more than 100 years, the company has developed a series of aluminum alloy materials that have made important contributions to the development of the aviation industry.
Alcoa is also involved in the development of the Airbus A380. In order to realize the integration and enlargement of aircraft structural parts, the company has developed a new type of aluminum alloy 7085 large forgings that can be used for the overall structure, with a section thickness of up to 300 mm. In the A380 project, the number of parts used in the 7085 forgings was reduced from 147 to 40, the number of fasteners was reduced from 1400 to 450, the weight was reduced by 20%, and the cost was reduced by 20% to 25%. Load carrying capacity and fatigue life have also been significantly improved.

Alloy family two: titanium alloy
Titanium and titanium alloys have low density, high specific strength (currently the highest in metal materials), corrosion resistance, high temperature resistance, non-magnetic properties, good structural properties and stability, and can be directly connected to the composite structure, and the thermal expansion between the two The coefficients are similar, it is not easy to produce electrochemical corrosion, and has excellent comprehensive performance. Therefore, titanium alloys are becoming more and more widely used in the aviation field.
In 1949, Douglas used titanium alloys for the first time on the engine compartment and insulation panels of the DC-7 transport aircraft. Lockheed's "Black Bird" high-altitude high-speed strategic reconnaissance aircraft SR-71, flying at speeds over Mach 3, when flying at high speed, the surface temperature of the body will exceed the limit of conventional aluminum alloy skin, if made of steel, the weight of the aircraft will Greatly increased, affecting flight speed and ceiling performance. Therefore, the SR-71's fuselage is made of titanium alloy, with a total weight of more than 30 tons, accounting for 93% of the aircraft's structural weight.
As people's performance requirements for aircraft continue to increase, the amount of titanium alloy used in civil aircraft is gradually increasing. The amount of titanium alloy parts on the early Boeing 707 was only 0.2% of the total weight of the structure, up to 15% of the latest Boeing 787.
In addition, titanium alloys are also the main materials for the manufacture of aero engines. For the J79 engine used in the early American F-4 fighters, the amount of titanium alloy was only 50 kg, less than 2% of the total weight. Today, most aircraft engines use titanium in amounts of 25% to 30% of the total engine weight. For example, the engine JT9D of Boeing 747 and 767 uses 25% of the total weight of the aircraft; the V2500 engine of the Airbus A320 uses 31% of the total weight of titanium.
Another major use of titanium alloys is as fastener materials such as bolts and rivets. These fasteners are small, but they are used in large quantities, and the use of titanium alloy fasteners can greatly reduce weight. It is estimated that 70% of the fasteners of the C-5 large transport aircraft are titanium alloy fasteners, and the aircraft loses about 1 ton.
Titanium 3D printing technology is now used in aircraft manufacturing. Titanium alloy 3D printing technology can eliminate the traditional mold manufacturing, which significantly extends the development time, and can manufacture high-precision, high-performance, high-flexibility and rapid manufacturing of metal parts with complex structures, thus providing rapid development of advanced aircraft structures. A powerful technical means.

Alloy family three: ultra high strength steel
Ultra-high-strength steel has many advantages in strength, rigidity, toughness and price, and has the characteristics of maintaining high life and high reliability under extremely high load conditions, and is widely used in the aviation field.
For example, the landing gear of an aircraft is subject to complex loads such as impact, and the load is huge. At the same time, the space of the landing gear is required to be as small as possible. The ultra-high strength steel has high absolute strength and good stability, so it is the material of choice for the landing gear.
In the 1960s, the United States successfully developed 300M ultra-high strength steel. The tensile strength of 300M steel is high, reaching more than 1860MPa. It has high transverse plasticity and good fracture toughness. Compared with low-strength ultra-high strength steel of the same strength, 300M steel has better fatigue resistance and lower crack growth rate in the medium. These features make 300M steel the main material for large aircraft landing gear.
In 1992, the United States developed the AreMet100. AreMet100 has the same strength level as 300M, but its corrosion resistance and stress corrosion resistance are much higher than that of 300M steel. It is the best ultra-high strength steel with the best comprehensive performance. The F-22 and F/A-18E/F use the AreMet100 as the main material for the aircraft landing gear.
Another application of ultra-high strength steel is as a base material for some special transmission components, such as bearings and transmission gears in aero engines. The working environment of bearings and gears of aero-engines can be described as “infernal”. They are not only subject to various stresses of compression and friction, but also must not cause cracks and other damage during use. Only ultra-high-strength steel Can take this responsibility. At present, only a few countries in the world have mastered the manufacturing technology of ultra-high-strength steel for aero-engine transmission components.

Alloy family four: magnesium alloy
Magnesium alloy is the lightest metal structural material with low density, high specific strength, strong seismic resistance and high impact load.
The earliest research on magnesium alloys in foreign countries was mainly in the field of spacecraft applications, and later gradually developed into the aviation field. In 1934, Germany began to apply aircraft parts made of magnesium alloy to the Fokker Fw-200 aircraft, mainly used in aircraft hoods, wing skins and seat frames, each aircraft sharing about 650kg of magnesium alloy material.
At present, the application of magnesium alloy materials in the aviation field mainly includes: aircraft frames, seats, engine casings, gear boxes and the like. In 2010, the US Federal Aviation Administration conducted a large number of complete flammability tests for magnesium alloy aircraft seats made of AZ31, WE43, etc., and compared the flammability and combustion duration of the two magnesium alloys.
Essex Aircraft's 190-8327L aircraft fuel tank made of magnesium alloy sheet and profile can reduce the weight by 0.144~0.168kg per liter compared with the fuel tank made of aluminum alloy. The maximum weight reduction of the entire aircraft can be achieved. 454kg.
At present, some high-temperature magnesium alloys such as WE43 and WE54 have been widely used in the transmission systems of new aerospace engine gearboxes and helicopters, such as Sikorsky's S-92 helicopter. These magnesium alloy materials are well suited to harsh environments such as high temperatures, corrosion, vibration and sand.
Along with the continuous development of aerospace metal materials, aircraft metal processing technology is also rapidly developing, such as large-wall aging forming technology, large-scale die forging manufacturing, 3D printing technology, advanced cementing technology, advanced welding technology.
When designing an aircraft, it is necessary to combine the advantages of materials, develop strengths and avoid weaknesses, and make the best use of materials, so as to maximize the performance of materials, truly achieve the safety and efficiency of aircraft structures, and achieve the purpose of reducing weight and reducing manufacturing and operating costs.

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