Influence of annealing temperature on microstructural evolution and tensile behavior of Ti-6Al-4V alloy manufactured by multi-directional forging

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 alpha phase (alpha p) and transformed /3 phase (/3t). With the increase of annealing temperature, the secondary alpha (alpha s) phase precipitates from the /3 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 degrees C has an excellent combination of strength and ductility, due to the larger content of the fine alpha s phase. All fracture surfaces contain massive dimples, which is a typical ductile fracture feature. The characteristics of microcracks, microvoids, and kinked alpha p/alpha l (equiaxed alpha p and lamellar alpha phase) phases are found near the fracture.