Influence of annealing temperature on microstructural evolution and tensile behavior of Ti-6Al-4V alloy manufactured by multi-directional forging
(Aviation Key Laboratory of Science and Technology on Advanced Titanium Alloys, AECC Beijing Institute of Aeronautical Materials, Beijing 100095, China)
Abstract: A range of annealing treatments were implemented to regulate the microstructure and mechanical properties of Ti-6Al-4V forging. The results show that both the as-forged and as-annealed microstructures exhibit a bimodal structure composed of equiaxed primary α phase (αp) and transformed β phase (βt). With the increase of annealing temperature, the secondary α (αs) phase precipitates from the β phase. There is no obvious texture and the crystal orientation is uniformly distributed. Meanwhile, strength initially increases and then decreases, whereas ductility remains largely unaffected. The alloy annealed at 860 °C has an excellent combination of strength and ductility, due to the larger content of the fine αs phase. All fracture surfaces contain massive dimples, which is a typical ductile fracture feature. The characteristics of microcracks, microvoids, and kinked αp/αl (equiaxed αp and lamellar α phase) phases are found near the fracture.
Key words: Ti-6Al-4V forging; annealing temperature; microstructural evolution; secondary α phase; tensile properties; ductile fracture