Effect of Process Parameters on Microstructure and Dynamic Compressive Property of Ti-6Al-4V Plates Fabricated via Friction Stir Welding

Abstract

The microstructure and mechanical properties of Ti-6Al-4V plates (thickness: 5 mm) welded via friction stir welding (rotation speed: 150-300 rpm, welding speed: 70-100 mm/min) were investigated. The microstructural investigation revealed that the nugget obtained at 150 rpm and 70 mm/min was composed of a mixed structure, whereas the other weld joints were composed of a fully lamellar structure. Transmission electron microscopy analysis revealed that fine recrystallized α-grains and dislocations occurred in the lamellar structure. The tensile tests showed that the tensile strength of all joints reached 96% of the tensile strength characterizing the base material. Moreover, the failure strain of each joint during tensile testing was > 13%. The weld joints with fully lamellar nuggets exhibited better dynamic compressive properties than the joints with mixed-structure nuggets. The results demonstrated that the recrystallized α-grains and dislocations are beneficial for enhancing the dynamic mechanical properties. The optimum dynamic mechanical response was obtained when a rotation speed and welding speed of 300 rpm and 100 mm/min, respectively, were employed as the welding parameters.