At present, the development achievements of China’s aviation industry have attracted worldwide attention. With the rise and rapid development of the aerospace industry, the integration and large-scale trends of titanium alloy complex components have become quite obvious. As an effective response, it is of great practical significance to study the precise plastic forming technology of titanium alloy complex components. The reason why titanium alloys are favored in the aviation industry is mainly because titanium alloys have the advantages of high temperature resistance, high specific strength, low density, high corrosion resistance, and the ability to be welded, so aerospace vehicles and space vehicles are improving their comprehensive For performance and reducing its own weight, titanium alloy materials will be given priority. Because the synthesis of titanium alloys and their components has a relatively high technical content, the amount of titanium alloy materials used has now become one of the important indicators to measure the advanced level of aviation (aerospace) aircraft. However, in order to optimize the total cost performance of aerospace (aerospace) aircraft, it is necessary to control the proportion of titanium alloys used. At present, the overall requirements for aviation (aerospace) aircraft in the field of aerospace are safe and reliable, long service life, excellent performance, high speed, and light weight. Among them, reducing the weight of the aircraft (aerospace) is important for increasing fuel and improving aircraft performance. is crucial.
II. Analysis of precision plastic forming technology for complex titanium alloy components
At present, the precision plastic forming technology of titanium alloy complex components mainly includes three kinds, namely powder metallurgy technology, isothermal forging technology and precision casting technology. The utilization rate of titanium alloy materials of these three technologies can reach the level of 70% to 90%, which has good production economy and can achieve net shape production. Because titanium alloy materials are recognized as very expensive materials, and waste materials are difficult to recycle and process, increasing the processing cost of titanium alloy materials, therefore, the selection of high utilization processing technology is the key to improving the cost performance of titanium alloy components.
- 1. Titanium alloy powder metallurgy technology
MLM (metal powder injection molding) technology is currently recognized as one of the most significant advantages of forming technology. It belongs to near-net forming technology and has unique advantages in manufacturing high-precision, high-quality complex parts. In the preparation of parts with complex shapes, the titanium alloy hot isostatic pressing powder metallurgy technology is relatively easy to operate, and the prepared titanium alloy parts are almost all net shapes, and their material properties and titanium alloys originally prepared based on forging materials processing technology The components are comparable. Moreover, the powder titanium alloy consolidated by hot isostatic pressing powder metallurgy technology can achieve full density, not only good microstructure, but also uniform structure, fine grain, no segregation and texture problems, its performance is not lower than the level of forgings .
At present, the foreign aerospace field has reached a relatively high level in the research of high-performance titanium alloy powder metallurgy technology, and some have been commercialized. Although China has also carried out a lot of research work on titanium alloy powder metallurgy technology, the research on high-performance titanium alloy powder metallurgy technology, especially key component high-performance titanium alloy powder metallurgy technology, still lags behind the foreign advanced level.
- 2. Isothermal forging technology
Relevant research on titanium alloy isothermal forging technology has a history of more than 30 years, and there are more than dozens of types of large titanium alloy forgings based on this technology. Data show that the projected area of titanium alloy forgings is currently 0.48 square meters. The research and application of this technology abroad are earlier than domestic ones, some of which are also quite representative. For example, the technology of isothermal forging and processing of nearly γ-TiAl alloy parts developed by the German GKSS research center is one of the typical representatives. Some other European and American countries have also made some achievements in the research of this technology, and already have mature hardware facilities, such as feedback system equipment, constant strain rate control equipment, and temperature control equipment. Although China’s titanium alloy isothermal forging technology started late, it has also achieved remarkable achievements. For example, China’s Baosteel Company successfully used isothermal forging technology to successfully trial-produce a 500 mm diameter TC17 titanium alloy integral disc and high-pressure compressor plate. The results show that the metal flow lines of the forging are reasonably distributed, and have good structure and performance.
In order to promote the development of isothermal forging technology to a deeper degree, the following key technologies need to be solved in future research: first, the structure performance control technology of large parts; second, the design technology of multi-directional loading forming mold structure of complex shape parts; again , The overall thin-walled parts forming labor-saving technology; finally, the titanium alloy parts precision forming metal flow control technology.
- 3. Precision casting technology
In recent years, titanium alloy precision casting technology has developed rapidly. For example, titanium precision casting + hot isostatic pressing + heat treatment technology has been developed to ensure that the quality of titanium alloy castings is close to β-annealed titanium alloy forgings; float melting casting technology has been developed. Casting with reduced pressure suction method, turbulence rarely occurs during pouring, almost no bubble inclusions, rarely casting defects. In the United States, the vacuum die-casting method has entered the practical stage as a new titanium casting method. This method does not produce pollution on the surface of the casting, the quality is relatively stable, and the subsequent pickling process is also omitted.
The United States Howmet, Boeing and the US Air Force Research Laboratory jointly developed thin-walled titanium castings. The nose caps and fireproof seals of the engine pylon of the C-17 military transport aircraft were selected, and each was replaced by an integral casting. A nose cap composed of Ti-6Al-4V alloy sheet metal parts and a fireproof seal composed of multiple parts and fasteners. After hard work, it has reached the thickness of 1.27mm and is applied in the newly produced C-17 aircraft. Domestically, the Beijing Institute of Aeronautical Materials has successfully cast a complex frame-shaped structure with a size of 630 mm × 300 mm × 130 mm and a minimum wall thickness of only 2.5 mm.
Problems with this technology, first of all, large titanium alloy components will be used more and more in critical parts that are prone to fatigue and fracture, but when large and complex thin-walled titanium alloys are cast, liquid metal flow forms part of the molding material into the metal flow after cooling. Inclusions can easily lead to the occurrence and propagation of cracks, especially shrinkage holes larger than 10mm in titanium alloy castings, which are difficult to flatten and weld in hot isostatic pressing. Secondly, the mold filling and solidification process of investment casting is prone to many casting defects such as air entrainment, inclusions, shrinkage holes, cold partitions, etc., which affects the performance of castings. Finally, although the vacuum die casting method does not have the above problems, it is only suitable for manufacturing parts with simple shapes. The maximum mass of the casting is 18 kg, the maximum size is 61 cm × 46 cm × 25 cm, and a maximum of 12 parts can be cast at a time.
In order to achieve the goal of reducing the weight of the aircraft, aerospace engineers usually adopt the overall structure rather than the original way of using small forgings to become large parts. This move not only improves the rigidity of the aircraft but also significantly reduces the weight of the aircraft. For titanium alloy materials, because of the difficulty of welding, the use of integral forming technology to make it a one-time integral component is the current development trend of titanium alloy structural parts manufacturing technology for aviation and aerospace vehicles, especially large, thin-walled, and complex , Overall, precision manufacturing technology is even more representative.