Correlation of Fracture Behavior with Microstructure in Friction Stir Welded, and Spin-Formed Al-Li 2195 Domes

Abstract

Single-piece, spin-formed domes manufactured from friction stir welded(FSW) plates of Al-Li alloy 2195 have the potential to reduce the costof fabricating cryogenic propellant tanks. Mechanical properties in thecompleted domes can be related directly to the final material conditionand the microstructures developed. However, these new fabricationtechniques have resulted in unexpected material challenges, such asabnormal grain growth in the weld nugget and the propensity for fracturein the adjacent thermo-mechanically affected zone (TMAZ). In this study,the microstructure and texture transformations within the TMAZ arerelated to fracture location in the vicinity of the weldment. Thetexture variations in the TMAZ are caused primarily by the varyingamounts of shear deformation introduced during the FSW process. Grainmorphology and microtexture characteristics are examined as a functionof location in the TMAZ via electron backscatter diffraction (EBSD). Astrong correlation between fracture location and the presence of texturebanding in the TMAZ is observed. The fracture path tends to follow adistinct region of low Taylor Factor (TF) grains.