Research On Diffusion Bonding/Gas Bulging Forming Technology Of TA7 Titanium Alloy Double-layer Structure

TA7 titanium alloy is a widely used α-Titanium alloy that has been used to make fuel tanks for missiles and turbine-boxes for supersonic aircraft.Due to the lack of research on new technologies such as near-net-sharp forming of TA7 titanium alloy,this paper explores the Diffusion Bonding/ Gas Bulging Forming Technology of TA7 titanium alloy.The deformation behavior of TA7 at high temperature and the effect of diffusion temperature on the Diffusion Bonding properties of TA7 was studied.By using the finite element analysis,the ideal Gas Bulging Forming pressure time curve of the double-layer structure is obtained.According to the test and simulation results,the technological parameters of Diffusion Bonding/ Gas Bulging Forming Technology of TA7 titanium alloy double-layer structure were formulated.In addition,the feasibility of Diffusion Bonding/ Gas Bulging Forming Technology is verified by finite element analysis method,and the technological scheme and die design of it are given.According to the high temperature tensile test results of TA7 titanium alloy,the following conclusions can be drawn: the maximum m value of TA7 titanium alloy was obtained at 930°C,followed by 870°C.But at the strain rate of 0.001 s-1 and tensile temperature of 870°C,TA7 titanium alloy had the best comprehensive performance.Too long heat preservation time will affect the degree of recrystallization and grain growth to influence the material elongation and lower tensile strength.The results of high temperature pre-tensile test show that it will affect the properties of the material at room temperature.The higher the pre-tensile temperature,the lower the elongation and the worse the plasticity of the material.In general,the tensile strength varies little at all pre-tensile temperatures.Therefore,it is better to choose the lower forming temperature within the temperature range of the research subject.According to the shear test results of the diffusion bonding test of TA7 titanium alloy,the shear strength bonding effect is better at 880～900°C,with an average value of around 570 MPa.From 880°C to 920°C,the shear strength decreases gradually with the increase of temperature.This point is also reflected in the result data of high temperature tensile elongation of TA7 titanium alloy at the same temperature range.The maximum shear strength of the joint is 619.38 MPa when the diffusion bonding temperature is 880°C.Considering the results of the study on high-temperature deformation behavior of TA7 titanium alloy,880°C was taken as the best diffusion bonding temperature parameter.The results of high temperature tensile test of TA7 titanium alloy were used for finite element simulation.It was found that the best gas bulging forming temperature was 870℃ while the stress concentration was the lowest.When forming at 870°C,the workpiece was basically moulded at 1563 s and completely moulded at 3000 s.The maximum forming pressure is 3.805 MPa.The thinning of wall thickness can be controlled under 10%.Software ABAQUS was used to simulate and compare the structural strength of TA7 titanium alloy with different technologies and different stiffener parameters.The simulation results show that the structural strength of the parts obtained by Diffusion Bonding/ Gas Bulging Forming is not lower than that obtained by the original forming technology.In addition,the radius of the contact fillet between the stiffener and the mold surface is 1mm,and the thickness of the stiffener is the plate thickness consistent with the mold surface(1.5mm),which are the most suitable.The forming of TA7 titanium alloy double-layer structure needs to begain with preforming,followed by Diffusion Bonding/ Gas Bulging Forming.