SPF/DB Processing And Assessment For Four-sheet Structure Combined With Solid Frame Of TA15Titanium Alloy

Superplastic forming/diffusion bonding (SPF/DB) completed forming anddiffusion bonding two working procedure in a heating cycle, has the characteristics oflow cost, high efficiency and nearly no margin, and the multi-sheet structure has theadvantages of good structural integrity, light weight, etc. Titanium alloy parts bySPD/DB show great superiority in reducing the production cost and the aircraft weight;therefore, the titanium alloy SPF/DB process is widely used in aerospace field.In this paper, the process and control method of SPF/DB was studied on the baseof TA15titanium alloy four-sheet structure combined with solid frame. After theanalysis of the four-sheet structure combined with solid frame, two bar trapezoid solidframes were used and symmetrically distributed between the core and the panel, thepanel preforming dies were designed, though the calculation of linear expansioncoefficient, the SPF/DB forming dies of four-sheet structure combined with solidframe were designed.The panel and core forming processes were simulated by MSC.MARC finiteelement simulation software, the influence of the arget strain rate and frictioncoefficient were analyzed on the panel thickness distribution, the influence of theargetstrain rate and the width of the diffusion bonding were analyzed on the corethickness distribution, and forming optimal parameters and time-pressure loadingcurve were obtained.According to the simulation results the panel preforming and the SPF/DB formingof four-sheet structure combined with solid frame were tested at920℃, a wholefour-sheet structure combined with solid frame was obtained, the overall effect wasgood, outer surface was smooth, and had no obvious defects; The thickness distributionof four-sheet structure combined with solid frame was measured, and explained thereasons for differences of the thickness.The microstructure changes of sheet and solid frame were analyzed before andafter the forming by OM, and discovered that the grain size of the panel, core and solidframe significantly grew up; diffusion bonding surfaces were observed among panel,core and solid frame by SEM, and the reasons affecting the effect of diffusion bondingwere analyzed.