Hot working of Ti-6Al-4V via equal channel angular extrusion

The deformation behavior of Ti-6Al-4V during high-temperature equal channel angular extrusion (ECAE) with or without an initial increment of upset deformation was determined for billets with either a lamellar or an equiaxed alpha preform microstructure. For conventional ECAE (ie., deformation by simple shear alone), flow localization and fracture occurred at temperatures between 900 degrees C and 985 degrees C. In contrast, billets deformed at temperatures between 845 degrees C and 985 degrees C using an initial increment of upset deformation immediately followed by the simple shear deformation of ECAE exhibited uniform flow with no significant cracking or fracture. A simple flow-localization criterion was used to explain the influence of preupsetting on the suppression of localization in billets with the lamellar microstructure. The suppression of flow localization for the equiaxed microstructure and the elimination of edge cracking for both types of microstructures were explained in terms of heat transfer (die chill) and workpiece geometry. Further evidence of the relative importance of microstructural and thermal effects was extracted from the results of two-pass extrusions, the first with upsetting and the second without upsetting.