Titanium alloy forging process is widely used in aerospace manufacturing industry, isothermal forging process has been used in the production of engine parts and aircraft structural parts; it is also more and more popular in automobile, power and ship industries.

Titanium alloy is characterized by small specific gravity, high strength, and good heat and corrosion resistance. It has become the main material of modern aircraft stress components, greatly reducing the weight of the aircraft. Among them, TC4 (Ti-6Al-4V) and TB6 titanium alloy forgings are widely used in aviation manufacturing.

Classification of titanium alloy and forging process

According to the microstructure at room temperature, titanium alloy can be divided into three types: α - type alloy, α + β - type alloy and β - type alloy. The thermoplasticity of α - and α + β - type alloy has little relationship with the deformation rate, while β - type alloy has good malleability, but low temperature may cause α phase precipitation.

According to the relationship between forging temperature and β transition temperature, the forging process of titanium alloy can be divided into conventional forging and high temperature forging.

Conventional forging of titanium alloy

The commonly used deformed titanium alloy is usually forged below β transition temperature, which is called conventional forging. According to the heating temperature of the billet in the (α + β) phase region, it can be divided into the upper two-phase region forging and the lower two-phase region forging.

Lower two phase region forging

The forging in the lower two-phase region is usually heated at 40-50 ℃ below the β transition temperature, at which the primary α phase and β phase participate in the deformation at the same time. The lower the deformation temperature is, the more α phases are involved in deformation. Compared with the deformation in β region, the recrystallization process of β phase in the lower two-phase region is accelerated rapidly. The new β grains formed by recrystallization not only precipitate along the original β grain boundary, but also appear in the β middle layer between β grain boundary and α sheet layer. The forging produced by this process has high strength and good plasticity, but its fracture toughness and creep properties have great potential.

Upper two phase region forging

It starts forging at 10-15 ℃ below the β / (α + β) transformation point. The final structure after deformation contains more β - transformation structure, which can improve the creep property and fracture toughness of the structure, and make the titanium alloy have plasticity, strength and toughness at the same time.

High temperature forging of titanium alloy

Also known as "β forging", it can be divided into two kinds: the first is the process of heating the billet in β zone, starting and completing forging in β zone; the second is the process of heating the billet in β zone, starting forging in β zone, and controlling a large amount of deformation to complete forging in two-phase zone, which is called "sub β forging". Compared with the two-phase forging, β forging can obtain higher creep strength and fracture toughness, which is also conducive to the improvement of the cycle fatigue property of titanium alloy.

Isothermal die forging of titanium alloy

In this process, the superplasticity and creep mechanism of the material are used to produce complex forgings, and the die is required to be preheated and kept in the range of 760-980 ℃; the hydraulic press applies pressure at a predetermined value, and the working speed of the press is automatically adjusted by the deformation resistance of the blank. As the mold is changed to be heated, it is not necessary to use the movable crossbeam so fast to avoid quenching. Many forgings used in aircraft have the characteristics of thin wall and rib height, so this kind of technology has been applied in aviation manufacturing, such as TB6 titanium alloy isothermal precision die forging worker of a domestic model machine.