Research On The Cooling Compression Of TC4 Titanium Alloy

TC4 titanium alloy is widely used in the aerospace field for its low density, high strength, good mechanical properties, excellent corrosion resistance and many other superior performance. However, due to its large deformation resistance and poor plasticity at low temperatures, the hot forging is the most commonly used forming method for TC4 titanium alloy.During the hot forging process for heavy forgings of TC4,the heating temperature of billet is usually about 950?, while the temperature of the mold is generally in the vicinity of 350?. The existence of the temperature difference makes the surface material of the forging actually experience a cooling deformation process. But in most conditions today, the parameters of TC4 under cooling compression are substituted by that of isothermal which leads to the defects of microstructure and properties.The main work of this paper is to make a comparative study of the flow behavior of TC4 titanium alloy in isothermal compression and cooling compression, establish a new constitutive model which can describe the flow stress in both conditions, and verify the model by forming tests of a “T” rib.First, contrast compression tests under isothermal and cooling conditions were conducted on the Gleeble-3500 thermal simulation testing machine. The results show that the flow stress at the same instantaneous temperature, strain and strain rate under isothermal were greater than that under the cooling conditions.Secondly, in order to more accurately describe the flow behavior of TC4 under different temperature conditions, a new constitutive model is proposed in this paper. By introducing the cooling rate ? makes it possible for the model to give an accurate prediction of the flow stress of TC4 under cooling conditions.Thirdly, XRD testing methods were used to detect the phase contents of ? and ?. The results show that the phase contents of ? in cooling conditions are significantly more than that in the isothermal cases, which can partly explain the difference in flow stress.Finally, a T-shaped rib-web part extrusion test were conducted in both the numerical simulation and experimental way to verify the model established in this paper and also give a hand to the design of the process parameters of TC4 titanium alloy in the practical applications.