The finite element software was used to simulate and analyze the hydroforming process of TC4 titanium alloy bellows based on the Johnson-Cook constitutive model and the ductile damage model.The influence of internal pressure,die fillet size and die spacing on the hydroforming of bellow was analyzed,and the optimized process parameters were obtained.Aiming at the titanium alloy tube that the outer diameter is Φ21.5 mm,the wall thickness is 0.16 mm,and the maximum diameter after forming is Φ31.5 mm,the optimum die radius of the hydroforming bellows is 4t (t is the thickness of tube),the hydroforming pressure is 42 MPa,and the die spacing is 8 mm.Comparing the simulation results with the experimental ones,it is found that there is a difference of 2％-3％ at the maximum reduction rate of the peak,and there is a difference of 1％-2％ at the end of the tube,which are mainly due to the assumption that total lubrication is used in the simulation process,while in the experimental process may be not,the greater the friction coefficient is,the larger the reduction becomes,and the experiment verifies the simulation accuracy.

The microstructure of the tube blank before and after welding was observed. Three rolls cold rolling with three passes was carried out, and the solution treatment was carried out between the passes. The results show that the weld microstructure is columnar dendrite microstructure; after cold rolling and solid solution treatment, the welding position on the pipe has been difficult to distinguish, and the original weld microstructure is completely transformed into homogeneous microstructure; after three-roller rolling, the strength of the welded joint is close to that of the base metal, the plasticity is obviously improved, and the strength is slightly higher than that of the base metal.