With China's national economy, science and technology development, aerospace, aviation industry in recent years ushered in a new development opportunity, especially in the national "big plane" project, civil aviation manufacturing industry will become a new economic growth point leading the development of the national economy, has a broad development prospects. Civil aviation manufacturing enterprises in order to continuously improve the advanced nature of the aircraft, reliability, applicability, increase the competitiveness of domestic aircraft in the international market, the choice of aviation manufacturing materials more and more demanding; titanium alloys are mainly characterized by a small specific gravity, high strength, and at the same time has a good heat resistance, corrosion resistance, to become the main choice of materials for the modern aircraft components, greatly reducing the weight of the aircraft, of which the TC4 (Ti-6AL-4V) is the main material of the aircraft. 6AL-4V) and TB6 titanium alloy forgings in aviation manufacturing applications.
According to the room temperature microstructure, titanium alloys can be divided into three types: α-type alloys, α + β-type alloys and β-type alloys, of which α and α + β-type alloys of thermoplasticity and the deformation speed of the relationship between the small, while β-type alloys have good malleability but the temperature is too low may cause α-phase precipitation. The forging process of titanium alloy is categorized into conventional forging and high temperature forging according to the relationship between forging temperature and β-transition temperature.
1. Conventional forging of titanium alloy
Commonly used deformed titanium alloys are usually forged below the β-transition temperature, called conventional forging. According to the billet in the (α + β) phase zone heating temperature, can be subdivided into the upper two-phase zone forging and the lower two-phase zone forging.
Lower two-phase zone forging
Lower two-phase zone forging is generally in the β transformation temperature below 40 ~ 50 ℃ heating and forging, when the primary α-phase and β the same time to participate in the deformation. The lower the deformation temperature, the more the number of α-phase involved in deformation. Compared with the β zone deformation, in the lower two-phase region of the β phase recrystallization process is dramatically accelerated, recrystallization of the formation of new β grains not only along the deformation of the original β grain boundaries precipitation, but also in β grain boundaries and α lamellae between the β interlayer appears. Produced by this process of forging high strength, good plasticity, but its fracture toughness and creep properties have great potential.
On the two-phase zone forging
It is in the β / (α + β) phase transition point below 10-15 ℃ temperature of the beginning of forging. The final organization after deformation contains more β-transformation organization, which can improve the creep properties and fracture toughness of the organization; make titanium alloy plasticity, strength and toughness.
2. High temperature forging of titanium alloy
Also known as "β forging", is divided into two kinds: the first is the billet in the β-zone heating, in the β-zone to start and complete the forging process; the second is the billet in the β-zone heating, in the β-zone to start forging, and to control a large deformation in the two-phase area to complete the forging process, referred to as "sub-beta forging Sub-β forging". Compared with the two-phase zone forging, β forging can get higher creep strength and fracture toughness, but also conducive to the improvement of titanium alloy fatigue performance.
3. Isothermal die forging of titanium alloy
The process makes use of the superplasticity of the material and the creep mechanism to produce more complex forgings, the requirements of the mold preheated and maintained in the range of 760 ~ 980 ℃; hydraulic press to a predetermined value of the pressure, the working speed of the press by the deformation of the blank resistance to automatic adjustment. Because the mold is changed to heating, do not need to use so fast moving beam to avoid rapid cooling. Aircraft with many forgings have thin-walled and rib high characteristics, so the process has been applied in the aviation manufacturing, such as a domestic aircraft TB6 titanium alloy isothermal precision die forging process.
