In the process of aviation manufacturing development, the replacement of materials presents high-speed changes, and materials and aircraft have been developing under the mutual promotion of each other. "A generation of materials, a generation of aircraft" is a true portrayal of the history of world aviation development. And new materials are an important foundation of aviation technology, and they are the forerunners of the upgrading of traditional industries and the development of high-tech industries. Regarding the development and application of new aviation materials such as titanium alloys, the reporter recently interviewed Cao Chunxiao, an academician of the Chinese Academy of Sciences.
The amount of titanium alloy is increasing. Reporter: Materials are the basis of aircraft manufacturing. Without new materials prepared by high-end technology, it is difficult for the development of the aviation industry to reach the cutting-edge. With the development of the aviation industry and the development of new models, the demand for aviation materials has increased compared with the past. What changes?
Cao Chunxiao: With the development of the aviation industry, the specific strength of the material is required to be higher and higher, and the performance is getting better and better. Now composite materials and titanium alloys are used more and more in aircraft and engines. Composite materials, for example, were rarely used in aircraft in the 1980s, but have developed rapidly in recent years. The latest Boeing 787 passenger aircraft accounted for 50% of composite materials, and titanium alloys accounted for 15%, breaking the historical record in the field of civil aircraft. The previous Boeing 777 passenger aircraft used only 10% of composite materials and only 8% of titanium alloys. The span is beyond imagination.
There are two main reasons for the large-scale application and development of composite materials and titanium alloys: one is that with the accumulation of material research and practical experience in application, the performance and reliability of materials are getting better and better; With the development of processing and manufacturing technology, the price of the material itself is also greatly reduced than before. Specifically, Ti-6AI-4V (TC4) titanium alloy was used in the past. Now we continue to use it, and we have also developed new varieties of titanium alloys with higher strength and other properties. After years of testing, many parts of the aircraft have begun to use these alloys. New titanium alloy. For example, the Boeing 777 passenger aircraft uses three grades of β-type titanium alloys, namely Ti1023, β21S, and Ti153 at same time. The Ti1023 titanium alloy forging used in the landing gear of the Airbus A380 has a weight of 3.2 tons and a length of 4.2 meters, which is currently the largest titanium alloy forging in the world. The unique properties of titanium alloys make its application prospects more extensive. Taking the anti-shelling ability as an example, because the anti-shelling ability of titanium alloys is significantly better than that of composite materials, the amount of composite materials used in US F-22 fighter jets has been reduced from the original 44.7% to the current 24%, while the amount of titanium alloys has increased to 41%. %. The use of titanium alloys in military aircraft is more than that in civilian aircraft, which is also for the purpose of enhancing combat effectiveness. In addition, the emergence of another new alloy with high fracture toughness and slow fatigue crack growth rate, high damage tolerance titanium alloy, is also an important reason for the increasing amount of titanium alloy in aircraft.
Aluminum alloys are still indispensable Reporter: Titanium alloys and composite materials are more and more widely used in aviation, so what about the development of other materials?
Cao Chunxiao: Composite materials, titanium alloys, aluminum alloys, steel, and superalloys are the five major candidates for aircraft and engines. They have been promoting each other in competition, complementing each other's advantages, and developing continuously. Although composite materials and titanium alloys have advantages in specific strength and corrosion resistance, aluminum alloys and steels have advantages in process performance and economic performance. Superalloys have a recognized primary position in aero-engines. It must also be pointed out that aluminum alloys and steel have been striving to develop new high-performance new varieties to continuously improve their competitiveness.
Therefore, the current general trend is that composite materials and titanium alloys are widely used, but aluminum alloys and steel are still indispensable and important aerospace materials. At present, the largest aviation forging in the world is aluminum alloy forging. A beam on the wing of the Airbus A380 uses aluminum alloy with a grade of 7085. The forging is more than 6 meters long and weighs 3.9 tons.
Reporter: Large-scale heavy equipment such as 80,000-ton large-scale die forging presses have come out one after another, which is not only the improvement of my country's reloading capacity but also the improvement of national strength. What is the significance of this for the development of aviation materials?
Cao Chunxiao: The structural integration of aircraft and engines is a very important direction for the development of modern aviation equipment. Integration can not only reduce structural weight, enhance reliability, improve assembly efficiency, but also reduce costs. Who can achieve structural integrity, who can develop rapidly?
The 80,000-ton large-scale die forging press of China Erzhong can forge extra-large forgings, which has changed the way of manufacturing aircraft structural parts by mechanical connection or welding in the past. It is very important to promote the large-scale integration of titanium alloy forgings and steel forgings. The 80,000-ton large-scale die forging press has surpassed the previous Russian 75,000-ton die forging press, which is the largest in the world. It solves the problem of whether my country can make extra-large forgings, and is of great significance for us to become a forging power, a titanium alloy power, and an aviation power.
The 80,000-ton large-scale die forging press can not only produce extra-large forgings, but also promote the integration of the structure, and also play a very important role in the precision of forgings (whether steel, aluminum alloy, titanium alloy, superalloy, and other material forgings). big boost. Compared with rough forgings, the tonnage of die forging presses required for precision forgings is increased by 2 to 4 times. At present, many forgings have "fat heads and big ears", and the utilization rate of raw materials is only about 10%, which wastes a lot of resources including raw materials and energy. After the precision of forgings, the cost of forgings and finished parts can be greatly reduced. Precision forgings can also improve reliability. In the past, the flow lines in the rough forgings were cut off, which would affect the performance of the aircraft. After the precision forgings are processed, most of the flow lines in the forgings can be well preserved, thereby improving the reliability of the aircraft. Therefore, whether it is to manufacture extra-large forgings or to improve the precision level of large forgings, it is necessary to use a large die forging press of 80,000 tons, thereby promoting the overall improvement of my country's forging level.
Forgings account for a large proportion of aircraft and engines, generally accounting for about 30% of the weight of the body structure and about 40% of the weight of the engine, and forgings are generally key parts and play a huge role. Therefore, my country must continuously improve its forging capabilities, increase its competitive advantage, and promote the development of the aviation industry.
The ability of independent innovation still needs to be improved Reporter: What is the international status of the development level of titanium alloy aviation materials in China? What are the gaps and deficiencies? What are the difficulties in the current development?
Cao Chunxiao: my country ranks first in the world in terms of titanium production, but it can only be called a titanium alloy powder. The development level of my country's aviation materials is also transitioning from a big country to a powerful country. As far as aviation materials are concerned, my country also needs to improve its independent innovation capabilities, enhance its original innovation capabilities, and develop more aviation materials with independent intellectual property rights that can be famous internationally.
At present, my country has basically the ability to develop the alloys that are already in use in the world and also has some process technologies with independent intellectual property rights. There are also difficulties. The main problem of aerospace materials such as titanium alloys lies in the stability of batch production, and sometimes quality problems occur during batch production. This problem is more of a production management problem and is influenced by human factors. Therefore, my country should strengthen production management and promote the numerical control of thermal processing as soon as possible to avoid fluctuations in product quality caused by various factors. It is the road we must take in the future to continuously strengthen the numerical control of thermal processing equipment and processes.
