Research On Superplastic Forming And Diffusion Bonding Technology Of TC4Titanium Alloy Rudder

Superplastic forming and diffusion bonding (SPF/DB) generally can be used to manufactureintegral multi-sheet structure within a single forming process. The formed structure is characteristicby good bending rigidity, remarkably load-bearing stability, superior surface quality, excellent shapeprecision and light structure weight, with good energy absorption and fatigue resistance ability.Moreover, the SPF/DB process reduces the cost dramatically. Hence, SPF/DB has become a importantand preferred method to manufacture aerofoil parts.However, the traditional process of SPF/DB has a series of disadvantages, including thedifficulty of coating stop-off, long time thermal exposure and low yield of the product. To solve theabove problems, laser welding can be introduced to reform the traditional SPF/DB method，improvingthe mechanical properties and increasing the yield. Therefore, it is extremely important andpractically valuable to do some research on the SPF/DB combined with laser welding for formingmulti-sheet structure of aerofoil parts. In this thesis, research on the laser welding and SPF/DBtechnology for Ti-6Al-4V titanium alloy rudder was carried out, and the sample of four layer structurewas fabricated successfully. The main researches are as follows:Based on the theory of SPF/DB, with other related theories, the SPF process of the core-sheetwas simulated in ABAQUS using the nonlinear finite element method. Then, the distribution ofthickness and stress condition were predicted and the pressure-time control curve under iso-strain ratewas obtained, which provide reference for the subsequent experiments.The laser penetration welding process for two sheets of Ti-6Al-4V titanium alloy was studied,the optimal welding parameters were obtained, and the core sheets of four-layer structure weresuccessfully welded. Then, the SPF/DB experiment was carried out to fabricate the rudder.Quality of the forming rudder was tested. It reveals that the performance of the rudder well meetthe requirement. The inner stiffeners are completely vertical and the distribution of thickness is quitehomogeneous, what is more, the bonding percent exceeds95%. Although microstructure investigationshows that the grain size grows up evidently, it is smaller than the grain size of traditional process.The result shows that the proposed process is feasible. It solves the problems of the traditionalSPF/DB process and extends the application of SPF/DB process.