The Microstructure Morphology and Texture Evolution of α‐Ti in Ti‐6Al‐4V Alloy During Friction Stir Processing With Low Rotation Speed and Traverse Speed

Friction stir processed Ti‐6Al‐4V alloys are successfully prepared under low rotation speed (≤200 rpm) and low traverse speed (≤50 mm min−1). The microstructure of the stir zone is homogeneous in thickness. Effects of process parameters on microstructure and texture evolution of α‐Ti in the stir zone during friction stir processing are clarified. It is found that traverse speed had a significant impact on microstructure in the stir zone. The equiaxed nano‐crystalline α‐Ti grains without texture formed via friction stir processing below β transus. The high temperature range and severe deformation range are overlapped when the samples are processed with low traverse speed. Dynamic recrystallization happened repeatedly and fast cooling inhibited grain growth when the stir tool moved away the stir zone. Ti‐6Al‐4V alloy shows shear texture after friction stir processing below β transus with higher traverse speed. β → α transformation occurred and lamellar α colonies formed during cooling stage above β transus when the rotation and traverse speed are increased. The microstructure morphology and texture strength of Ti‐6Al‐4V plates could be regulated by combining of heating and cooling stages during friction stir processing. This paper is concerned with the microstructure morphology and texture evolution of α‐Ti in Ti‐6Al‐4V alloy during friction stir processing with 100–200 rpm and 25–50 mm min−1. The equiaxed nano‐crystalline α‐Ti grains without texture are found near the stir tool. Grain growth occurs and shear texture forms when the tool left away from the stir zone.